Table of Contents
Thus far we have discussed macronutrients and micronutrients, and diets can be constructed with these in mind. However, we also briefly touched on phytonutrients, and there are far too many dietary compounds to attempt to construct a diet to include these in specific amounts. To get around this issue, and additionally as many people do not want to actually consider the macro & micronutrients specifically, recommendations can be made regarding intake of specific food groups. These can be much easier to follow without needing to look at nutrition labels at all.
In this lesson, we will discuss food groups as a whole and then more specifically grains, fruits & vegetables, dairy, meats, eggs, nuts, and oils. We’ll go over the general intake amounts recommended by the dietary guidelines and additionally discuss to what degree this is supported by recent evidence.
Food groups for general health considerations
The 2020-2025 Dietary Guidelines for Americans (DGA) recommends consuming a variety of vegetables from all of the subgroups (dark green, red & orange, beans/peas/lentils, starchy, and other), fruits (especially whole fruits), grains (at least half should be whole), fat-free or low-fat dairy, a variety of protein foods (including seafood, lean meats & poultry, eggs, nuts/seeds/soy), and oils.
Example: The DGA specifically recommends if consuming a 2000 kcal/d diet:
- Vegetables: 2.5 cup-equivalents daily with 5.5 cups of red/orange vegetables weekly, 5 cups of starchy vegetables weekly, 1.5 cups of dark green vegetables weekly, 1.5 cups of beans/peas/lentils weekly, and 4 cups of other vegetables weekly
- Fruits: 2 cup-equivalents daily
- Grains: 6 ounce-equivalents daily with at least half of these as whole grains
- Dairy: 3 cup-equivalents daily
- Protein foods: 5.5 ounce-equivalents daily with 8 ounce-equivalents weekly of seafood, 26 ounce-equivalents weekly of meats/poultry/eggs, and 5 ounce-equivalents weekly of nuts/seeds/soy products
- Oils: 27 grams daily
They specify eggs should be kept to 3-4 ounce-equivalents weekly for vegetarians (this would be 3-4 eggs, the set the limit at 4 if consuming 2,800+ calories daily).
For a list of the various foods that fall within each food group, see the footnote of Table A3-2 in the DGA.
Note: Converting between ounce-equivalents and serving size may seem confusing. As serving sizes can be arbitrary, using ounce-equivalents should be more accurate. However, using ounce-equivalents is more cumbersome as these are not typically included on nutrition labels. The DGA defines ounce-equivalents as follows:
A separate group of authors has published several analyses of prospective studies in the last few years attempting to determine the impact of different food groups on a variety of health outcomes, including all-cause mortality (“ACM”), coronary heart disease, stroke, heart failure, type 2 diabetes mellitus, and weight gain.(Schwingshackl, 2017a; Bechthold, 2019; Schwingshackl, 2017c, Schlesinger, 2019) Combining the consistent results within these analyses, they find an “optimal” food group consumption consisting of:
- 3 servings of whole grains daily
- 3 servings each of fruits & vegetables daily
- 1 serving of nuts daily
- 1 serving of legumes daily
They do find a benefit of fish for ACM (maximal at 2 servings daily) & dairy for type 2 diabetes prevention (maximal at 3 servings daily) but not for the other outcomes. They consistently find worse health outcomes with red meat, processed meat, sugar-sweetened beverages, and eggs. Of note, they are not recommending eating only the above (as this would not yield nearly enough calories), rather a daily diet should include at least the above to promote better health.
These authors also performed a separate analysis of randomized trials examining intermediate disease markers (including blood lipid profiles, glucose and insulin markers, blood pressure, and c-reactive protein (a marker of inflammation)).(Schwingshackl, 2018) They find the healthiest food groups in this analysis to be nuts, whole grains, legumes, fish, and fruits & vegetables, with less healthy effects seen with refined grains, red meat, eggs, dairy, and much worse effects with sugar-sweetened beverages.
These findings are largely in line with the DGA. Some differences are due to the way the DGA classifies protein-rich foods (which contains multiple food groups including meat, nuts, eggs, etc). Other differences arise depending on if recommendations are being normalized to a certain level of caloric intake versus simply reporting what is observed to be associated with the best health outcomes in the literature.
Note: Any time a certain food group or item is promoted or discouraged it is important to consider what the replacement in the diet will be as this will determine the overall health effect. As one example, if somebody normally eats 10 servings of whole grains daily and no fruits or vegetables, their health will likely improve by taking out 4 servings of grains and replacing them with 4 servings of fruits and vegetables. However, if they replace those 4 servings with processed meat their health will likely worsen. Thus, it’s difficult to discuss food groups in isolation without considering replacement items.
With this background of what large comparative literature shows, let’s now look at the literature of specific food groups in more detail.
Several analyses of whole and refined grains have been performed over the last several years.
Impact of whole grains on body weight
A 2020 systematic review and meta-analysis (SR/MA) of randomized controlled trials indicated that while observational studies typically show a benefit of whole grains regarding body weight and obesity, the controlled trials in this review indicate there is no measurable benefit of whole grain consumption on body composition outcomes.(Sadeghi, 2020) They actually find that increasing whole grain consumption slightly increased BMI in individuals who were overweight, obese, or otherwise unhealthy. However, it is important to realize that most of the studies included simply added whole grains to the participant’s diets and did not actually substitute out different foods, and it is not surprising that body weight was gained when there was no additional attempt to decrease caloric consumption.
Impact of whole grain on health outcomes
A 2016 SR/MA of prospective studies showed significant health benefits of 90 grams (3 servings) of whole grains daily with risk reductions of 15-22% for ACM, cardiovascular disease (“CVD”), and total cancer. Further milder benefit was seen with intake up to 7 servings of whole grains daily.(Aune, 2016b)
A 2018 SR/MA of prospective studies showed a significant benefit of whole grains for ACM (with linear increased benefit up to 140 grams daily (~5 servings)).(Zhang, 2018) They did note that several studies do not define what they consider to be “whole grain” and several studies consider foods where >25% of the grains are whole grains to be a whole grain food. For this reason it can be hard to accurately quantify the impact of whole grains.
A 2020 umbrella review of observational studies regarding whole grain consumption and health outcomes concluded there is convincing evidence of a decreased risk of colorectal cancer and type 2 diabetes mellitus with increased whole grain consumption.(Tieri, 2020) There was also evidence showing a possible association with decreased risk of cardiovascular mortality, colon cancer, and prostate cancer, and limited evidence suggesting benefit of for ACM, cancer mortality, and stroke.
In addition to dietary fiber, there are many different phenolic acids and other phytonutrients that may account for some of the health benefits seen with whole grain consumption.(Călinoiu, 2018)
Note: One may think with all that we hear about whole grains and the clear health benefits that it would be easy to determine how much whole grain is present in a food based on the nutrition label. Well, the FDA issued a draft guidance on this topic back in 2006… and as far as I can tell they still have not finalized this.
Thus, while a product that has 100% whole grains on the nutrition label should only include whole grains, if a product states that it contains whole grains it is unclear what percent of the grains are actually whole. Of note, a 1 ounce-equivalent of whole grains contains 16 grams of whole grains. Thus, as in the example above, if someone is aiming for 6 ounce-equivalents of grains daily and wants at least 3 to be whole grains, they need to consume 48 grams of whole grains.
Are refined grains healthy or not?
Whole grains are typically touted as healthy for their fiber and micronutrient profile, but that doesn’t mean refined grains are inherently harmful. Previous meta-analyses have found no significant association of refined grains with ACM, BMI, CVD, stroke, or even type 2 diabetes mellitus (a possible exception with diabetes is when consuming large amounts of rice).(Gaesser, 2019) Additionally, refined grain products are commonly fortified and that can help increase healthy nutrient consumption for people who do not eat many whole grains.(Jones, 2020)
Rather than discouraging refined grains, it may be best to simply encourage increase whole grain consumption (for reasons indicated above) and to not worry about refined grain consumption assuming total caloric intake is appropriate. This would also be consistent with the DGA as it recommends that half of one’s grains should be whole grains, implying half can be refined.
Tip: For people who are dieting to lose weight it is important to realize that refined grain products may be less satiating, which can make weight loss more difficult. Refined grain consumption, especially >3 servings daily, has been associated with weight gain.(Schlesinger, 2019) Additionally, as discussed in Lesson 6 added sugar is generally advised to be kept at <10% daily calories, so if one wishes to eat a significant amount of refined grains it would likely be best to choose options keeping this added sugar threshold in mind.
Should gluten be avoided?
Gluten has received a large amount of press over the last several years. There is unanimous consensus that individuals with Celiac disease benefit from following a gluten-free diet, and it’s thought that roughly ~1% of the population has this disease.(Leonard, 2017) The large point of contention is whether individuals who do not have Celiac disease also can benefit from a gluten-free diet.
Non-celiac gluten sensitivity (NCGS) describes individuals without Celiac disease but who still seem sensitive to gluten. Depending on the exact definition used and method of diagnosis, anywhere from 0.5-6% of people may have this.(Caio, 2017) However, when testing individuals who believe they have this by giving them other components of wheat, some of them will have the same symptoms, implying it may not be the gluten but other aspects of wheat (ie, amylase-trypsin inhibitors) that are causing the symptoms.(Mumolo, 2020) In one analysis only 22% of people suspected of having NCGS developed symptoms with a blind gluten challenge.(Leonard, 2017)
Instead of gluten it may be FODMAPs (fermentable oligo-, di-, mono-saccharides and polyols) that are causing symptoms, as people who follow a gluten-free diet typically will decrease their FODMAP consumption when doing so. Many patients with NCGS have been diagnosed with lactose intolerance, fructose intolerance, small-intestine bowel overgrowth, or microscopic colitis, and a gluten-free diet may prove helpful by decreasing exposure to the actual underlying triggers.(Lerner, 2019) Gluten-free diets can additionally be deficient in several micronutrients if one is not careful to plan out the diet well.
At this point in time there is no strong evidence base supporting health benefits of gluten-free diets for the vast majority of people who do not have reproducible symptoms upon gluten exposure.
Based on all of the above, one should strive to consume at least 3 servings of whole grains daily with potential benefit seen with up to 7 servings. If counting calories then as many servings of refined grains as desirable is likely okay assuming this doesn’t displace other healthful nutrients in the diet (ie, fruits, vegetables, healthy fat sources, etc). For people who are not counting calories and who also are not attempting to gain weight, caution is warranted regarding too many servings of refined grains as these may not be very filling and can lead to overconsumption of additional food, leading to problems with weight gain. Limiting to 3 servings daily may be advantageous in this situation. There is no benefit to avoiding gluten unless reproducible symptoms occur with gluten exposure.
Fruits and vegetables
Several analyses of fruits and vegetables and their impacts on health outcomes have been performed in recent years.
Impact of fruits and vegetables on body weight
Certain fruits and vegetables have a proportionally large amount of fiber, which can aid satiety and make it easier to lose weight when consumed. For that reason, including large amounts of fruits and vegetables while on a calorie-restricted diet can be helpful. However, simply adding larger quantities of fruits and vegetables to one’s diet has not been associated with weight loss in and of itself.(Wallace, 2020) Thus, adding additional fruits & vegetables for the sole purpose of attempting to lose weight will likely not prove effective unless one is making a conscious effort to decrease caloric consumption.
Impact of fruits and vegetables on health outcomes
A 2017 SR/MA of prospective studies noted benefits of increased fruit and vegetable intake for CVD, total cancer, and ACM.(Aune, 2017) A maximum benefit for cancer risk was seen at 550-600 grams (7-7.5 servings) of combined fruits and vegetables daily, and a maximal benefit for ACM was seen at 800 grams (10 servings) daily. However, even with only 200 grams intake they found a risk reduction for ACM of 10%, for cancer of 3%, and for CVD of 8%, so even just 2.5 combined servings will yield benefit. A 2019 umbrella review of research syntheses found evidence is strongest for a beneficial impact of increased fruit & vegetable consumption for CVD while there is weaker evidence supporting a variety of other health conditions.(Angelino, 2019) A 2019 SR/MA showed that for most examined diseases consuming 300 grams daily of combined fruits and vegetables can decrease disease risk by 10-30%.(Yip, 2019)
Tip: To save money, consider purchasing canned or frozen fruits & vegetables. While it is a somewhat popular belief that fresh fruits and vegetables are healthier than their frozen equivalents, the literature indicates there is no substantial difference between the two.(Bouzari, 2015) Even with small differences, when considering the cost it can be a better value to obtain canned or frozen products.(Miller, 2014) Additionally, there is concern about keeping fresh products in the refrigerator for extended periods of time as this can cause loss of nutrition.(Li, 2017) Thus, to save cost without any substantial loss of overall nutrition, consider purchasing canned or frozen.
Mechanism for health benefits
A 2018 review on the contributions of fruits & vegetables to health highlights the wide variety of phytonutrients that they contain and some of the various mechanisms by which they can impart benefit.(Yahia, 2019) A 2019 umbrella review also highlights the various health effects on a wide variety of different conditions and discusses some of the bioactive compounds that likely contribute to these findings.(Wallace, 2020) They conclude the strongest benefits may come from cruciferous vegetables, dark-green leafy vegetables, citrus fruits, and dark-colored berries.
100% fruit juice, unlike sugar-sweetened beverages, seems to only minimally contribute to weight gain.(Benton, 2020) While 100% fruit juice will not have any fiber, many of the other phytonutrients found in fruits will be present, and for this reason 100% fruit juice can have health benefits.(Ruxton, 2021) A recent analysis found unsweetened fruit juice was not associated with several examined health outcomes, though it is possible relatively low intake would have precluded any associations being found.(Fardet, 2019) For people who do not meet general recommendations for overall fruit and vegetable consumption, supplementing this with 100% fruit juice in moderation may prove beneficial. Sweetened fruit juice and canned fruits (generally sweetened), however, do seem to increase risk of negative health outcomes significantly.(Fardet, 2019)
The evidence is clear that eating many servings of a variety of different fruits and vegetables is health-promoting, with benefits potentially seen with up to 10 combined servings daily. Meaningful benefits are seen with substantially less than this. Thus, I recommend consuming a variety of different types and colors of fruits and vegetables, aiming for at least 5 combined servings (400 grams) daily, knowing additional benefit can likely be attained with even higher amounts. Whether fruits and vegetables are purchased fresh, frozen, or canned is a matter of preference. If it is unrealistic to obtain several servings daily for whatever reason, consuming 100% whole fruit/vegetable juice (not sweetened) for 1-2 servings daily is a reasonable substitute.
With dairy products there is some controversy regarding health benefits and risks of whole-fat and reduced-fat dairy products. In addition, there is some concern of dairy consumption contributing to prostate cancer, which I will discuss thoroughly below.
Health effects in children
A 2016 SR/MA of prospective cohort studies with children found increased dairy intake was associated with lower odds of being overweight or obese.(Lu L, 2016) A 2017 SR of randomized controlled trials in children and adolescents, however, concluded that dairy consumption does not have a significant effect on body composition but does aid bone development.(Kouvelioti, 2017) A 2020 SR of studies in children found that neither whole-fat nor reduced-fat dairy had strong associations with body composition or cardiometabolic health, with authors concluding there is no strong evidence to support limiting whole-fat dairy intake in children, although they acknowledge more trials are needed.(O’Sullivan, 2020)
Thus, given the known benefit of dairy & calcium consumption for bone development in youth, it seems advantageous for children and adolescents to aim for 3 servings daily, without strong preference for a specific fat content. Of note, dairy intake has been associated with increased acne, which can certainly be a concern as acne typically worsens in adolescence. However, this has largely been seen with reduced-fat milk as opposed to whole-fat milk, yogurt, or cheese, so if this becomes a problem with reduced-fat milk intake one can try to adjust dairy sources accordingly.(Aghasi, 2019)
Health effects in adults
In 2018 a SR/MA of observational studies concluded that dairy, milk, and yogurt are all associated with decreased risk of metabolic syndrome, with this being largely driven by whole-fat dairy as low-fat dairy did not have an impact.(Lee, 2018) A 2018 SR/MA of prospective cohort studies found that studies consistently show total & reduced-fat dairy have neutral or inverse associations with type 2 diabetes mellitus as well as other cardiometabolic disease processes.(Soedamah-Muthu (2018) A 2019 SR/MA of randomized controlled trials concluded that higher dairy intake was associated with very minimal decreases in insulin resistance, waist circumference, and body weight; the results they report are likely not clinically significant.(Sochol, 2019)
A 2020 umbrella review of observational studies found dairy had beneficial effects on several disease processes, though some findings were restricted to reduced-fat dairy products.(Godos, 2020) However, they also found that dairy can increase the risk of prostate cancer and Parkinson’s disease. A 2014 meta-analysis specifically examining the increased risk of Parkinson’s disease found a small absolute increase in risk due to dairy intake, predominantly in men, with 2-4 new cases per 200 grams daily intake of milk and 1-3 new cases per 10 grams daily intake of cheese per 100,000 person-years.(Jiang, 2014)
Regarding cancer as a whole, a 2019 overview of reviews showed that for most cancers there was no significant association of dairy intake and change in risk.(Jeyaraman, 2019) Possible exceptions included colorectal cancer where 20 reviews showed no association but 9 found a decreased risk, endometrial cancer where only 1 review was found and this showed an increased risk, non-Hodgkin’s lymphoma where 5 reviews found no association but 4 found an increased risk, and prostate cancer where 13 reviews found no association, 2 found a decreased risk, and 13 found an increased risk. A 2016 meta-analysis examining cancer mortality risk found an increased risk only with prostate cancer, no other types.(Lu W, 2016)
Dairy and prostate cancer
Regarding prostate cancer more specifically as that is a large concern seen in the literature regarding increased dairy consumption, a 2015 SR/MA specifically examined the link between dairy products, calcium, and prostate cancer risk.(Aune, 2015) This included 32 prospective studies and found small relative risks of prostate cancer development with increased dairy consumption in the 1.03-1.14 range per serving of total or reduced-fat milk, no significant association with whole milk, and when comparing high versus low consumption, relative risks of 1.07 for cheese & 1.12 for yogurt.
As stated above, a 2016 meta-analysis examining cancer mortality risk found an increased risk only with prostate cancer.(Lu W, 2016) Here they only included two studies, and for high compared to low whole milk intake the relative risk of prostate cancer mortality was 1.50 with a 95% confidence interval of 1.03-2.17. For reduced-fat milk the risk was 1.00 with a 95% confidence interval of 0.75-1.33. Since then a 2017 prospective study has found whole milk intake to be significantly associated with increased risk of death once diagnosed with localized prostate cancer, while reduced-fat milk intake was not associated with an increased risk of death, though there are small numbers and wide confidence intervals in this study.(Downer, 2017) A separate prospective study published in 2019 however finds no association of dairy intake and prostate cancer incidence overall and only a small increased risk of late-stage prostate cancer with regular-fat dairy and a small increased risk of advanced prostate cancer with 2% milk.(Preble, 2019)
In 2019 an overview of SR/MAs was published regarding milk/dairy product consumption and prostate cancer risk & mortality, citing several of the references discussed above through 2016.(López-Plaza, 2019) They include 6 total studies and find that for total prostate cancer the relative risk of high vs low consumption ranged from 1.09-1.68 for total dairy, 1.11-1.50 for milk, 0.74-1.18 for cheese, and 0.95-1.03 for other dairy. For advanced prostate cancer and prostate cancer mortality they note there was no statistically significant association seen. They note that the relative risks have decreased with sequential meta-analyses as new literature has emerged.
Note: It is not clear to me why the authors here state no association with prostate cancer mortality was seen as they do include (Lu W, 2016) which shows a statistically significant association between whole milk consumption and prostate cancer mortality.
A separate review in 2019 attempting to examine the link between dairy intake and prostate cancer and the various proposed mechanisms finds that much of the literature is inconsistent but nonetheless most of it does point to an association.(Vasconcelos, 2019)
Thus, overall it seems there probably is a small increased risk of prostate cancer with dairy consumption, at least at levels of typical consumption, though it’s unclear if it’s the dairy itself that is contributing or pesticides/hormones/other factors that are present in dairy products. If that is the case than organic dairy products may be safer, but this still remains to be seen. Given no other commonly significantly harmful risks seen with dairy consumption and the association with several health benefits, I do not believe that the concern of prostate cancer warrants elimination of dairy from one’s diet, but for men who are concerned by this limiting dairy to 2-3 servings daily may be wise, though more research needs to be done.
Whole-fat vs reduced-fat?
Several analyses have been done considering differential health effects of reduced-fat vs. whole-fat dairy.(Mozaffarian, 2019; Astrup, 2019) Collectively these tend to show few if any significant detriments comparing whole-fat relative to reduced-fat dairy, and at times positive outcomes are associated with whole-fat dairy that are not seen with low-fat dairy, particularly with yogurt and cheese, though occasionally the opposite is seen.(Hirahatake, 2020) The lack of detriment with whole-fat dairy despite the relatively high saturated fatty acid content is likely due in part to different saturated fatty acid profiles in dairy vs non-dairy products, as this seems to impart different health effects.(Unger, 2019)
Of note, many of these associations are seen in observational studies where total consumption of whole-fat dairy products may not be very high. A recent study did show detrimental effects of high levels of dairy fat (41 grams daily, for comparison a typical serving of whole-fat milk has 8 grams of fat) which were significantly attenuated by substituting some of the saturated fatty acid content with monounsaturated fatty acids (by feeding the cows 1 kilogram of sunflower oil daily for 4 weeks prior to dairy collection).(Vasilopoulou, 2020) Thus, at typically consumed dairy levels choosing whole-fat options may not be detrimental, but if consumed at high levels the large amount of saturated fat may impose harm.
Many people find as they get older that they become intolerant of dairy products. This is due to a reduction of the lactase enzyme that lines the small intestine and helps to digest the lactose sugar found in dairy. For people where this is a problem they may find supplementing with Lactaid to be helpful. Of note, many people will have only partial lactose-intolerance and still be able to consume some dairy without symptoms, typically no more than 12 grams of lactose daily. Additionally, many people who have symptoms with certain dairy products will not have symptoms with yogurt, particularly strains of yogurt with more live active cultures as these microorganisms can help break down the lactose so it does not cause symptoms.(Kok, 2018)
Throughout youth consuming 2-3 servings of dairy daily seems beneficial for bone development, without significant preference for fat content unless saturated fat intake is otherwise high in one’s diet (in which case choosing a reduced-fat dairy option makes more sense). Choosing reduced-fat options for weight concerns may also be beneficial if either tracking calories or in some way restricting ad-libitum food intake. In adulthood dairy intake is associated with some health benefits, but there seems to be a weaker association than with grains, fruits, and vegetables. As a source of calcium dairy will still be beneficial, but for those with lactose intolerance who do not wish to consume Lactaid and cannot or choose not to consume yogurt, it does not appear many significant health benefits will be missed with low dairy intake if calcium intake is achieved elsewhere in the diet. Soy milk (with calcium fortification) would be a reasonable alternative in this regard.There is likely an association between dairy products and prostate cancer that needs to be better characterized; if this is a specific concern keeping dairy intake on the lower end is reasonable.
Tip: There are other micronutrients in milk beyond just calcium. As discussed in prior lessons, if you choose not to consume dairy and you are concerned about missing out on any specific nutrients, feel free to plug your typical diet into cronometer.com to see if you are deficient in anything.
Many people think science goes back and forth about whether eggs are healthy or not, and this is for good reason as there has been a lot of evidence published both ways. I will highlight only a few studies below and conclude with advice from the American Heart Association.
A 2020 umbrella review of egg consumption and human health found that there is no consistent evidence of a harmful effect on most health outcomes examined.(Marventano, 2020) A 2020 SR/MA of prospective cohort studies examining the risk of egg consumption and type 2 diabetes mellitus found that overall there was a relative risk of 1.07 with 1 egg consumed daily, with a risk of 1.18 in US cohorts and no increased risk in European & Asian cohorts.(Drouin-Chartier, 2020) Of interest, randomized trials, such as the DIABEGG study, have shown eggs can be a regular part of a weight maintenance or weight loss program in individuals with prediabetes or type 2 diabetes and have no harmful effects on any of the classic cardiovascular risk factors.(Fuller, 2018)
A 2019 analysis of 6 prospective cohort studies examining CVD outcomes found that for an additional 0.5 eggs daily the hazard ratios for incident CVD and ACM were 1.06 & 1.08, respectively; this was no longer significant when adjusting for cholesterol consumption.(Zhong, 2019) After this was published an analysis of the PURE, ONTARGET, and TRANSCEND cohorts was published that did not replicate the prior finding but did find and increased risk of heart failure with the latter two cohorts at higher egg consumption levels.(Dehghan, 2020) Of interest, research has generally shown that egg consumption in typically consumed quantities does not negatively impact cholesterol levels or other CVD risk markers.(Clayton, 2017)
The American Heart Association weighs in
With this somewhat conflicting data regarding the impact of egg intake and heart health (as well as additional data I have not included), in 2020 the American Heart Association published a science advisory discussing both egg and cholesterol consumption.(Carson, 2020) They highlight observational studies generally do not show a negative impact of cholesterol consumption and that there is lots of confounding in studies with eggs. They performed a meta-regression of trials that had similar ratios of polyunsaturated-to-saturated fatty acids that varied between 155-1000 mg of cholesterol daily and found a small positive association between dietary cholesterol and total cholesterol levels with no significant association between dietary cholesterol and LDL or HDL cholesterol individually. They conclude that healthy individuals can include up to 1 whole egg daily in their diet without issues, people with abnormal lipid levels should be cautious of increased dietary cholesterol intake, and due to the highly nutritious content of eggs older individuals with normal cholesterol can have 2 eggs daily in the context of a heart-healthy dietary pattern.
Eating 1 whole egg daily seems safe. Given the small amount of literature regarding egg intake beyond 1 daily, as well as the frequent association of egg consumption with unhealthy lifestyle habits (at least in US studies), it is hard to derive an evidence-based viewpoint on greater egg intake. Short-term trials such as the DIABEGG trial listed above have shown higher egg intake can be included in healthy weight-maintenance or weight-loss efforts. Of note, perhaps 20-25% of people are hyperresponders to cholesterol consumption (meaning their cholesterol levels go up considerably more with cholesterol intake than those who are not hyperresponders).(Clayton, 2017) For individuals who do wish to consume multiple eggs daily, it may be best to obtain a blood lipid profile prior to increasing egg consumption. Repeating the blood lipid profile at least 4 weeks after increasing egg consumption would then show if an individual’s cholesterol numbers worsened significantly, and if so it would be worth considering cutting back on the egg intake.
For an extended period of time, as evidenced in the DGA, the majority of the literature indicated that eating patterns that include seafood are associated with positive health effects, as are eating patterns low in red meat and processed meat. They do make a distinction for lean red meat, however, stating that when consumed in recommended quantities this can also be part of a healthy eating pattern.
The NutriRECS publications
However, at the end of 2019 a new series of systematic reviews culminating in a guideline suggested that current levels of processed meat and unprocessed red meat intake do not need to be decreased. This garnered a lot of press and many responses. I’m going to briefly discuss this here.
Cohort studies and cardiometabolic outcomes
One of these SR/MAs evaluated cohort studies examining the impact of red & processed meat consumption on risk for ACM & cardiometabolic outcomes.(Zeraatkar, 2019a) They found studies through July, 2018 from multiple databases and performed a final MEDLINE search for further references in April, 2019. They considered 120 grams to be a serving of unprocessed red meat, 50 grams to be a serving of processed meat, and 100 grams to be a serving of meat from mixed sources. Results showed that decreasing 3 servings per week of red/processed meat yielded relative risk for ACM of 0.93/0.92, cardiovascular mortality 0.90/0.90, total stroke 0.94/0.94, fatal stroke 0.94/0.95, total myocardial infarction 0.93/0.94, and type 2 diabetes mellitus 0.90/0.78, all with evidence rated low or very low due to the observational design of the studies. The GRADE system was used to determine the level of evidence.
Note: GRADE by default will rank SR/MAs of observational evidence as low quality initially. Thus, even if all of the cohort studies were perfectly done the level of evidence would have still initially been considered low. This is in part as GRADE was not developed initially with long term nutrition studies in mind but rather was developed to help address clinical questions. A separate system, NutriGrade, has been proposed to better evaluate nutrition literature specifically.(Schwingshackl, 2016)
They note in the text that per GRADE the level of evidence can be upgraded if a dose-response relationship is seen, and they do see a dose-response relationship, but they actually choose not to upgrade the level of evidence due to concerns that other dietary confounding is what actually explains the dose-response relationship. They imply that if red & processed meat were the primary drivers of the negative health outcomes then larger associations would be seen.
Note: Keep in mind the results are considering a reduction of 3 servings weekly; reducing servings by 1 serving daily would thus yield stronger associations as they do see evidence of a dose-response relationship.
Additionally, it does not logically make sense to me that they would not upgrade the evidence due to concern for confounding as a primary reason that GRADE downgrades observational research in the first place is due to the concern for unmeasured confounding. Thus, to not upgrade it essentially punishes the literature base twice for unmeasured confounding.
Randomized trials and cardiometabolic outcomes
A second of these SRs evaluated randomized trials examining the impact of red meat intake on cardiometabolic & cancer outcomes.(Zeraatkar, 2019b) They searched for trials in a similar manner as the above-mentioned SR/MA and found 12 unique randomized trials. They did not find any trials involving processed meat so this was not included. Of the 12 trials they found, only the Lyon Diet Heart Study & the Women’s Health Initiative (WHI) actually addressed ACM & other major cardiovascular disease outcomes. The former only had 605 people and per the authors was stopped early presumably due to an unrealistic large benefit.
Note: I do not think it is fair to just assume the results of the Lyon Diet Heart Study were unrealistic. There are certainly fair criticisms that can be made, however.(Kris-Etherton, 2001)
Therefore, they only present the results of the WHI for the ACM and CVD outcomes. Thus, this systematic review actually only includes 1 trial for the main outcome components. The WHI enrolled postmenopausal women and was actually designed to study the impact of a low-fat diet. The low-fat group decreased their red meat consumption by ~20% (1.4 servings per week). Unsurprisingly with such a small decrease in red meat consumption, no impact was seen on ACM, CVD, T2DM, cancer, or quality of life.
The NutriRECS guideline
I will not discuss the other analyses in detail but these include a SR/MA regarding the impact of red & processed meat on cancer incidence & mortality in cohort studies, a SR/MA regarding the impact of red & processed meat on cardiometabolic & cancer outcomes in cohort studies, and a SR/MA on health-related values & preferences regarding meat consumption.(Han, 2019; Vernooij, 2019; Valli, 2019) This culminated in a guideline that I will now address.(Johnston, 2019)
In this guideline they acknowledge that they ignore any environmental & animal welfare concerns as they just want to focus on the health aspects. Additionally, their target audience is people who consume red meat or processed meat (thus, they are not trying to convince non-meat eaters to begin eating meat) and they take the perspective of individual decision making rather than a public health perspective.
Note: This last point may seem like semantics but it is actually quite relevant for their conclusions. From a population health perspective even a small decrease in risk can have a significant impact when applied to millions of people. For example, a 1% decrease in risk applied to 1 million people may benefit 10,000. From an individual perspective, however, a 1% decrease in risk may not be a very strong motivational factor to change habits that have already been ingrained.
For both unprocessed red meat & processed meat they suggest continuing current intake rather than decreasing intake by 3 servings weekly, and they consider this a weak recommendation. Of note, only 11 of the 14 panel members agree with this; 3 believe they should advise decreased consumption. They base these recommendations on the low quality of evidence and the small absolute risk reduction seen by decreasing intake 3 servings weekly, while also considering that their SR on values indicates omnivores will not want to decrease meat consumption.
There has been much commentary on this new literature.(Correspondence, 2020) Dissenters highlight the fact that some studies were excluded, using GRADE was not appropriate, and the portion size they use is smaller than most prior analyses, which decreases the significance found.(Fadnes, 2020; Qian, 2020; Neuhouser, 2020) People in favor of it point to the fact that the analyses were very comprehensive(Dyer, 2019), and that confounding likely explains the small associations that are seen.(Correspondence, 2020) There has also been concern of conflicts of interest on both sides.(Rubin, 2020)
Interpretation of the guideline
My takeaway is that I do not believe their guideline is consistent with the evidence they put forth. They find risk reduction with smaller amounts of red & processed meat intake even when considering a reduction of only 3 servings weekly, and as indicated above they evaluate the evidence in a biased fashion due to the inherent flaws of using the GRADE approach for this type of analysis. Additionally, while the risk of confounding is always present in observational studies and it is certainly possible unmeasured confounding may account for the observed decrease in risk, to simply state that is the explanation without providing a rationale is in my opinion inappropriate.
Generally with nutrition literature evidence is considered stronger when randomized trials support the large observational findings. When this does not occur the concern for confounding is greater. However, a recent meta-analysis of randomized controlled trials showed that replacing both red meat and lean red meat with an isocaloric equivalent of plant-based foods yielded a significant benefit for total and low-density lipoprotein cholesterol levels.(Guasch-Ferré, 2019) Additionally, a recent SR/MA found processed meat increases the risk of colorectal cancer in a dose-response fashion (given a dose-response relationship it is less likely for confounding to account for the full association).(Händel, 2020)
More recent US cohort analyses do show concerns of red meat consumption, at least pertaining to incident type 2 diabetes.(Würtz, 2021) In a recent analysis of the PURE study (a prospective cohort study including many countries), while unprocessed red meat consumption was not found to increase the risk of mortality or cardiovascular disease, processed red meat did have this effect (with hazard ratios ~1.50 and an evident dose-response relationship).(Iqbal, 2021) Of note, the PURE study participants averaged only 37 grams of unprocessed red meat daily, considerably less than in other cohorts where an increased risk was found. As indicated above, differences in portion sizes may underlie the variable results that are seen.
Tip: For those who do consume red meat, benefits of lean red meat have been seen relative to non-lean red meat.(Guasch-Ferré, 2019) As lean red meat can be relatively expensive, one option is to ground beef and rinse/blot out the fat thoroughly. This can convert beef that is initially 70% lean to >90% lean, yielding a healthier product while saving money.(Love, 1992)
Other types of meat
White meat (poultry) is generally not associated with significant positive or negative health outcomes when consumed in typical ranges. Fish intake, on other hand, is associated with several positive health outcomes, and a recent umbrella review found that this is most prevalent for most assessed conditions at 2-4 servings weekly, with better effects seen with intake of fish high in essential fatty acids.(Li, 2020)
Note: One must take care not to consume fish with too much mercury. This is especially true for women who are or may become pregnant as well as children. The below card is in accordance with the DGA regarding concerns of mercury. Of the “Best” choices, the following may be higher in the desirable omega-3 fatty acids: salmon, herring, Atlantic and Pacific mackerel (not King mackerel, which is high in mercury), sardines, trout, pacific oysters, shad, and anchovy. Whenever purchasing fish with a goal of obtaining omega-3 fatty acids be careful to avoid purchasing products that have had the fat removed.
Fish intake should be consumed at the levels indicated above, ideally 2-3 servings weekly of fish rich in the omega-3 fatty acids EPA & DHA while also being low in mercury. Meat otherwise is generally not associated with the healthiest eating patterns but there isn’t direct evidence to indicate a negative health impact of unprocessed poultry. Red meat seems more problematic in excess, though occasional consumption of lean red meat is unlikely to significantly increase one’s risk of harm. When consumed, lean red meat will generally be healthier than non-lean red meat. Processed meat, whether red or poultry, does seem harmful and intake should likely be limited for health purposes.
Tip: As alluded to within the NutriRECS guideline, some people love meat and do not want to give it up. For people who are going to eat a lot of meat (multiple servings daily) no matter what, considerations to make this healthier include:
- preferentially choosing fish (canned, fresh, or frozen is fine) that is low in mercury
- preferentially choosing unprocessed poultry
- if consuming red meat, preferentially choosing lean options or removing as much fat as possible (perhaps add extra seasoning to make this more palatable)
- trying to avoid processed meat
- attempting to cook at relatively low temperatures to decrease the production of harmful byproducts
Nuts are generally considered health promoting with no significant risk of harm, the one obvious excepting being for people who have an allergy to nuts. Another exception is specifically with Brazil nuts (see below).
Overall health effects
A 2016 SR/MA of prospective studies, considering a serving size of 28 grams for total nuts, 10 grams for tree nuts, and 10 grams for peanuts, found that 1 serving daily decreased the risk of CVD by 21%, 25%, and 34%, respectively.(Aune, 2016a) For ACM the risk reduction was 22%, 18%, and 23%, respectively. For cancer the risk reduction was 15% and 20% for peanuts and tree nuts, respectively. No statistically significant decrease with peanuts was seen per daily serving but in a high vs low intake analysis they did see a decrease of 7%. Several of these analyses did not see improvement beyond 10-15 grams of total nuts intake daily. They note that previous randomized controlled trials have found results consistent with this.
A separate 2016 umbrella review of MAs evaluating the impact of nuts and risk for CVD found evidence consistent with these findings, as did a 2018 review of MAs on nuts & cardiometabolic diseases, as well as a separate 2018 review.(Schwingshackl, 2017b; Kim, 2018; Bitok, 2018) Collectively these show positive effects for most cardiometabolic outcomes with the exception of type 2 diabetes and stroke risk, where there seems to be no or at most minimal effect.
Tip: Despite nuts possessing a relatively large amount of fat, even when consumed at high quantities they do not appear to lead to weight gain.(de Souza, 2017) This is likely due to a combination of their effect on satiety, decreased caloric consumption later in the day, and less caloric yield from nuts than would be expected by their fat content. Thus, including nuts while losing weight can be beneficial.
In 2017 a SR of different types of nuts & health outcomes found that almonds, even up to 100 grams intake daily, does not cause weight gain but at lower levels can improve blood lipid parameters.(de Souza, 2017) Walnuts also decrease CVD risk and can aid inflammatory processes as well as improve endothelial function likely due to their high concentration of antioxidants. Pistachios also can aid blood lipid levels, inflammatory markers, and glucose metabolism. Peanuts are able to increase satiety, in part likely due to having higher protein & fiber content relative to tree nuts. Brazil nuts have significant antioxidant properties due to their selenium content. Hazelnuts and cashews have less direct literature but are also thought to yield health benefits. A 2020 review highlights the different phytonutrient profiles in the various types of nuts that may account for potential differences in health effects, but also reaffirms that all commonly consumed types seem to be health-promoting.(Alasalvar, 2020)
Note: Brazil nuts contain a high amount of selenium, with different analyses finding different amounts. One serving will yield selenium intake well above the tolerable upper limit (above which there may be negative health effects). In small quantities (ie, 1-3 daily) these are safe to consume, but beyond that they should only be eaten sparingly.
Other than Brazil nuts, the other types can be consumed in large quantities with little risk of harm. Eating at least 0.5 servings daily (14 grams) and preferably 1 serving daily for general health benefits is advised. All types seem healthy and while they individually have different phytonutrient profiles, I have seen no indication that any one type is significantly healthier than any other. There seems to be no significant harm of intakes well beyond this level, so nuts can make an excellent snack
Oils are used in a variety of cooking processes and can additionally be used as a topping for food items such as bread and salad. The various composition of the oils helps dictate both their health properties and in what way they may best be used for cooking. The figure below shows differences in oils based on their fatty acid content. Of note, while not commonly considered when denoting the health properties of oils, oils can have many other phytonutrients with various health benefits as well.(Teasdale, 2021)
Considerations with olive oil
As one example, research has shown olive oil consumption to have several health benefits.(Foscolou, 2018) Depending on the degree of processing this may be considered extra virgin olive oil (EVOO, obtained simply by pressing olives, and thus this type retains the most healthful nutrients (ie, phenolic compounds)), virgin olive oil, refined olive oil, or pomace oil (this does not have many health benefits as most the nutrients have been removed). Different regions even within one country may have olives with different nutrition content. Olive oil has a fatty acid content that is ~70% monounsaturated fatty acids, ~15% polyunsaturated fatty acids, and ~15% saturated fatty acids. Thus, this is a source of healthy fats without significant saturated fatty acid content. As virgin oils typically have a greater quantity of phytonutrients it is best to use them as toppings and to only expose them to light heat as with higher heat more of the nutrients will be lost.(Ng, 2019)
Tip: It can be tricky to obtain olive oil that is not adulterated. Essentially, high quality extra virgin olive oil is more expensive to produce than other types, and if you mix it with other types it may not be obvious to a typical consumer. Thus, many brands are adulterated in this fashion. This is actually a common problem worldwide.(Mailer, 2020) In the United States the California Olive Oil Council has a strict certification process. I recommend when purchasing olive oil to get a brand with the “COOC” seal on it as that will likely be legitimate. This will be more costly than other brands; whether the higher quality product is worth the cost will be based on how frequently a person uses the olive oil as well as personal preference.
Considerations with cooking
For cooking processes there are two major considerations. One is the smoke point, the temperature above which the oil starts to smoke. Ideally for frying and other high temperature cooking an oil with a smoke point above 200 degrees Celsius should be used.(Ng, 2019)
Tip: Avocado oil is healthy and has the highest smoke point of all commonly used oils. For people who do not intend to fry foods at high temperatures very frequently, spending some extra money to obtain avocado oil for this purpose can be worthwhile.
The other consideration when choosing a cooking oil is the generation of undesirable oxidation products. These can have negative health effects on a variety of different body systems and do not seem to have any health benefits.(Falade, 2017) This is more likely to occur with oils that have a high concentration of polyunsaturated fatty acids (avocado oil has <15% polyunsaturated fatty acids). Cooking at low heat for the shortest time possible will help prevent the formation of oxidation products (see note below).
One option to help maximize health benefits (as well as to provide a different culinary flavor) is to blend oils together, which can change the smoke point, increase stability to oxidation, and combine health properties of different types of oils.(Hashempour, 2016) This can be considered in settings where cooking oil is used very frequently.
Overall, for individuals who wish to make cooking oil choices as simple as possible, obtaining a high quality extra virgin olive oil for non-cooking consumption and avocado oil for high temperature cooking should yield good health outcomes. For individuals who want to experiment more, keep the above information in mind.
Note: I alluded to preparation methods briefly above but did not discuss these in detail. That is because even within one food group, such as vegetables, there can be different impacts on different nutrients with different methods of cooking, making it very difficult to provide firm recommendations.(Fabbri, 2015) From a safety standpoint it’s generally considered harmful to consumed oxidized cholesterol products.(Vicente, 2012) These tend to increase with prolonged cooking at higher temperature, increased time in the refrigerator prior to consuming, increased exposure to air, and increased exposure to light. Thus, trying to minimize these factors may help prevent damaging compounds from being formed. If interested, a recent review compiled data regarding how various cooking methods impact different cholesterol oxidation products in a variety of different food groups.(Maldonado-Pereira, 2018)
There are many considerations when choosing what foods to eat. To summarize the above:
- Whole grains, fruits, and vegetables all appear to have significant health benefits without much risk of harm and the benefits continue to increase potentially up to 7 servings daily for wheat and a combined 10 servings daily for fruits and vegetables.
- Refined grains do not seem inherently harmful though should be limited when keeping total caloric intake and added sugar in mind. Gluten should not be avoided unless there is consistent development of symptoms with its introduction.
- Nuts, with the exception of Brazil nuts, do not seem to impose a risk of harm with elevated intakes, and most benefit is seen with intake levels of 1 serving daily (28 grams)
- Dairy can be a great source of calcium as well as some protein but there does not seem to be much evidence of benefit with high levels of intake for overall health. There is potential risk of harm given elevated saturated fatty acid consumption and, in men, a potential increased risk of prostate cancer. Thus, limiting dairy to no more than 3 servings daily for men and using reduced-fat versions if going beyond this intake level may be advantageous. The link with prostate cancer, and the small link with Parkinson’s disease, require further study.
- The jury remains out on eggs; at this point it seems safe to consume 1 whole egg daily and potentially more if consuming a heart-healthy diet without significant cardiovascular risk factors. More research is needed to better determine why the controlled trials do not indicate the same level of risk seen in some, but not all, of the prospective cohort studies.
- Fish consumption is generally correlated with positive health outcomes at any typical level of intake; caution to avoid sources with significant mercury should be taken. Dietary patterns with elevated meat consumption otherwise are generally associated with worse health outcomes, though there is likely confounding of other lifestyle factors and multiple different types of meat in these diets. Unprocessed poultry seems fairly neutral with respect to health, and lean red meat seems relatively safe at low levels of consumption. Non-lean red meat and processed meat are associated with worse health outcomes and their intake should be reserved for occasional use.
We have now gone over the health implications of nutrition considering the nutrients of the foods and drinks we consume as well as the food groups themselves. After reading all of the lessons thus far it should be possible to construct a diet aimed to achieve a healthy body composition and to improve overall health. In the next lesson we will discuss the implications of the timing of when we eat.
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