Lesson 10: Food Groups (Grains, Fruits and Vegetables, Nuts, and Oils)

Table of Contents

Introduction

Thus far I have discussed macronutrients and micronutrients, and diets can be constructed with these in mind. However, I 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 and the next lesson, I will discuss food groups. In this lesson I will discuss food groups as a whole and more specifically grains, fruits & vegetables, nuts, and oils. In the next lesson I will discuss the somewhat more controversial topics of dairy, eggs, and meats. I’ll go over the general intake amounts recommended by the dietary guidelines and additionally discuss to what degree this is supported by recent evidence.

Note: While not a food group, water intake itself needs to be considered somewhere, and this is generally considered health-promoting. As recently reviewed, there is a growing body of research suggesting that insufficient water intake can contribute to cardiometabolic and kidney disease, even if enough water is consumed to prevent frank dehydration.(Johnson, 2022) Therefore, you can have “underhydration” without being dehydrated. While it is easy to track water you drink, it is more difficult to track how much water is in the foods you consume. Thus, it is likely best to drink sufficient water to ensure your urine remains a pale, light yellow color. If you drink a lot of water and your urine remains darker then consider discussing with your healthcare provider.

Food groups for general health considerations

Different sources of literature have attempted to compile generally healthy dietary advice into beneficial dietary plans.

Dietary Guidelines for Americans

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 2,000 kcal/day 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

The DGA specifies eggs should be kept to 3-4 ounce-equivalents weekly for vegetarians (this would be 3-4 eggs, they 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 following table shows how the DGA defines ounce-equivalents. However, it’s not necessarily accurate to assume all ounce-equivalents are actually equal; this can be considered a limitation of using ounce-equivalents as a standardization metric.(Park, 2021)

Taken from the DGA

In 2021 a systematic review (SR) that was conducted to help inform the DGA was published associating dietary patterns with all-cause mortality (“ACM”).(English, 2021) The authors found that a healthier dietary pattern generally consisted of greater intake of vegetables, fruits, legumes, nuts, whole grains/cereals/nonrefined grains, unsaturated vegetable oils, fish, and when included lean meat or poultry. Healthier dietary patterns generally included less intake of red & processed meat, high-fat dairy, refined grains, and sweets.

Other published literature

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 ACM, coronary heart disease (“CHD”), stroke, heart failure, type 2 diabetes mellitus (“T2DM”), and weight gain.(Schwingshackl, 2017a; Bechthold, 2019; Schwingshackl, 2017c, Schlesinger, 2019) Combining the consistent results within these analyses, they found “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 intake for ACM (maximal at 2 servings daily) & dairy for T2DM prevention (maximal at 3 servings daily) but not for the other outcomes. They consistently found 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 found 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: In 2021 a separate analysis was conducted regarding dietary recommendations for prevention of atherosclerosis, where for each food group the authors performed a systematic search for meta-analyses of prospective cohort studies evaluating CHD and cardiovascular disease (“CVD”) incidence and mortality.(Riccardi, 2021) Based on this, the authors recommend consuming:

  • at least 2 servings of vegetables, fruits, and whole grains daily
    • they indicate 1 serving of fruits or vegetables is 200 grams
  • at least 1 serving of low glycemic index refined cereals, nuts & seeds, extra-virgin olive oil or non-tropical vegetable oils, and yogurt daily
    • examples of non-tropical vegetable oils include sunflower, safflower, corn, and soybean
  • 4 servings of legumes and fish weekly
  • no more than 1 egg daily
    • they caution that individuals with hyperlipidemia, diabetes, or those who consume high amounts of saturated fat may want to restrict eggs to 3 days weekly (see further discussion of eggs in Lesson 11 as the concern with diabetes may be unfounded)
  • no more than 3 servings of white meat, cheese, and milk weekly
    • of note, in the text they note that white meat has not been found to be associated with CHD or CVD
    • additionally, in the text they suggest it is ok to have one serving of milk daily
    • the text also does not provide a rationale for limiting cheese to 3 servings weekly as the evidence they cite does not suggest harmful effects above this
  • no more than 2 servings of high glycemic index refined starchy foods, red meat, and butter weekly
    • see below for further discussion regarding refined grains and see Lesson 6 for a discussion regarding the glycemic index as this concern may be unfounded
  • processed meat infrequently
  • minimal amounts of sugar-sweetened beverages or artificially-sweetened beverages (see further discussion of artificially-sweetened beverages in Lesson 6 as this concern may be unfounded)
  • up to 3 cups of tea or coffee daily
  • up to 10 grams of chocolate daily

American Heart Association advice

The American Heart Association near the end of 2021 published a statement offering broad dietary advice for cardiovascular health.(Lichtenstein, 2021)) You can read their statement here; the abstract, associated table, and figure provide a general overview of the heart-healthy dietary pattern they recommend. I have not reproduced the images here as they are protected by copyright.

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, I will now discuss the literature of specific food groups in more detail. I will discuss the health and body weight implications in specific sections, but in general any body weight impact associated with specific foods or food groups is quite small.(Jayedi, 2022) Total calories are the main driver of body weight changes, while the foods and food group considerations have much larger impacts on overall health.

Grains

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 (“RCTs”) found that while observational studies typically showed a benefit of whole grain intake regarding body weight and obesity, the controlled trials in this review indicated there is no measurable benefit of whole grain consumption on body composition outcomes.(Sadeghi, 2020) The authors actually found that increasing whole grain consumption led to a small increase in body mass index (“BMI”) in individuals in overweight or obesity categories or who were otherwise unhealthy. However, it is important to realize that most of the studies included simply added whole grains to the participants’ diets and did not actually substitute out different foods; it is not surprising that body weight was gained when there was no additional attempt to decrease caloric consumption.

Impact of whole grains on health outcomes

Several reviews regarding whole grain consumption have been published:

  • A 2016 SR/MA of prospective studies showed significant health benefits of 90 grams (3 servings) intake of whole grains daily with risk reductions of 15-22% for ACM, 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 intake daily (~5 servings)).(Zhang, 2018) The authors 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 2018 review demonstrated that 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)
  • 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 T2DM 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 for ACM, cancer mortality, and stroke.
  • A 2022 dose-response MA of prospective studies found increased whole grain consumption lead to a decreased risk of diabetes, with a maximal benefit at 60 grams whole grain intake daily leading to a ~20% reduction in T2DM risk.(Ghanbari-Gohari, 2022)
  • A 2022 SR/MA including 24 articles with 68 studies found that higher levels of whole grain intake lead to decreased risks of stroke, coronary heart disease, CVD, and ACM, with a 6-8% risk decrease per 30 grams intake for the latter 3 conditions.(Hu, 2022)

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. Furthermore, there is no uniform definition for what constitutes a whole grain food.(Du, 2022)

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, if someone is aiming for 6 ounce-equivalents of grains daily and wants at least 3 to be whole grains, then they need to consume 48 grams of whole grains per day.

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 MAs have found no significant association between refined grains and ACM, CVD, stroke, or even T2DM (a possible exception with T2DM is when consuming large amounts of rice).(Gaesser, 2019; Gaesser, 2022 – this author is a member of the Grain Foods Foundation and Wheat Foods Council; Hu, 2022) A 2020 SR/MA of trials comparing whole grain to refined grain consumption found whole grains yielded small, likely clinically meaningless benefits to triglycerides, hemoglobin A1c, and C-reactive protein, although oats particularly had a larger beneficial impact on cholesterol changes and many studies included subjects who were healthy at baseline (which would make it less likely to see substantial changes in these metrics).(Marshall, 2020) Of note, 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 attempting to lose weight, a 2021 SR/MA found that whole grain options relative to refined grains can benefit hunger, satiety, fullness, and desire to eat, though portion sizes included were relatively large.(Sanders, 2021) Of note, most of the studies did not include the whole grain options with more fermentable fiber (ie, oats) which would be expected to have a more significant impact on appetite. While the included trials did not incorporate weight loss, it is logical to assume that any benefit of whole grains on appetite will extend to weight loss efforts as well, and thus when dieting to lose weight it may be helpful to prioritize whole grain options.

For people who are attempting to gain weight, refined grain consumption, especially >3 servings daily, has been associated with weight gain.(Schlesinger, 2019) If satiety is preventing you from consuming enough calories to gain weight then it makes sense to prioritize refined grain options (while still consuming a few servings of whole grains for the health benefits). As discussed in Lesson 6, added sugar is generally advised to be kept at <10% of daily calories, so if you wish 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. Of note, many people with autoimmune diseases find some benefit with gluten-free diets, but it seems many of these individuals also have Celiac disease, potentially unknowingly.(Lerner, 2021)

Non-celiac gluten sensitivity (“NCGS”) describes individuals without Celiac disease but who still seem sensitive to gluten. Depending on the exact definition used and the 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) Of note, gluten-free diets can be deficient in several micronutrients if you are 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.

Recommendations

Based on all of the above, you should strive to consume at least 3 servings of whole grains daily with potential benefit seen with up to 7 servings. If counting calories, you can likely include as many additional servings of refined grains as desirable 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 undesirable 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; this can aid satiety and make it easier to lose weight when consumed. For this 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 you are making a conscious effort to decrease caloric consumption.

 

Impact of fruits and vegetables on health outcomes

Several reviews regarding fruit and vegetable consumption have been published:

  • 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 the authors found a risk reduction of 10% for ACM, 3% for cancer, and 8% for CVD, 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)
  • A 2020 review examined the impact of various fruit and vegetable sources on CVD, CHD, and stroke incidence and mortality and found benefits with all sources.(Zurbau, 2020) For most outcomes there was a 2-7% decreased risk per daily serving of total fruits and vegetables.
  • A 2021 umbrella review evaluating the impact of fruit intake on health outcomes found that increasing fruit by 1 serving daily can decrease the risk of CVD, stroke, and CHD by 3-8%, and by increasing fruit intake to 100-500 grams daily the risk of T2DM decreases by 8-12%.(Sun, 2021)

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 nutrients.(Li, 2017) An additional benefit of canned fruits is the long shelf life; if possible purchase them in water or otherwise in an unsweetened form, ideally with the peel intact if possible (for increased micronutrient content).(McGinnis, 2020)

Thus, to save cost without any substantial loss of overall nutrition, consider purchasing canned or frozen. This can be particularly helpful if a pandemic occurs again and the produce supply decreases sharply.

Mechanism for health benefits

A 2018 review on the contributions of fruits & vegetables to health highlighted the wide variety of phytonutrients that they contain and some of the various mechanisms by which they can impart benefit.(Yahia, 2019) A 2020 umbrella review also highlighted the various health effects on a wide variety of different conditions and discussed some of the bioactive compounds that likely contribute to these findings.(Wallace, 2020a) The authors concluded that the strongest benefits may come from cruciferous vegetables, dark-green leafy vegetables, citrus fruits, and dark-colored berries. A 2021 review highlighted the various classes of compounds providing different colors in vegetables and the health benefits associated with these classes, showing each colored vegetable has compounds with potentially several different health-promoting properties.(Sharma, 2021)

Fruit juice?

100% fruit juice, unlike sugar-sweetened beverages, seems to only minimally contribute to weight gain.(Benton, 2020) While 100% fruit juice will not have much, if 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) A review on apple juice notes that more benefits should be expected from cloudy juice rather than clear juice as the additional processing steps to generate clear juice will remove additional nutrients.(Vallée Marcotte, 2022) A more recent analysis found that 100% fruit juice at up to 1 cup daily does not lead to increased risks of diabetes or meaningful weight gain.(Chen, 2023) For people who do not meet general recommendations for overall fruit and vegetable consumption, supplementing with 100% fruit juice in moderation may prove beneficial. Sweetened fruit juice and canned fruits (generally sweetened), however, do seem to increase the risk of negative health outcomes significantly.(Fardet, 2019)

Recommendations

The evidence is clear that eating many daily 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% fruit/vegetable juice (not sweetened) for 1-2 servings daily is a reasonable substitute.

Nuts

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). Also, technically peanuts are a legume and not a nut but I am discussing them here as I’m not specifically addressing legumes separately (though legumes do have several health benefits).(Didinger, 2022)

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 total nuts and tree nuts, respectively. There was no risk reduction of cancer incidence for 1 serving of peanuts, but in a high vs. low analysis the authors did see a decreased risk of 7%. Several of these analyses did not see improvement beyond an intake of 10-15 grams of total nuts daily. The authors noted that previous RCTs 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) A 2020 MA found regular nut consumption was associated with a 10% decrease of both cancer incidence and cancer mortality, with tree nuts but not peanuts leading to a significant decrease in cancer incidence (subgroups by type of nuts were not done for cancer mortality).(Zhang D, 2020) A 2021 umbrella review of MAs evaluating the impact of nuts and legumes on various health measures found evidence of benefit for both regarding CVD and some evidence for nuts as protective against cancer and stroke.(Martini, 2021) A 2022 SR/MA including 17 publications found that higher nut intake was associated with a 10% decreased risk of cancer, 14% decreased risk of lung cancer, 21% decreased risk of gastric cancer, and a 12% decreased risk of cancer mortality; this reduction in the risk of cancer mortality also extended to peanuts.(Cao, 2023) With just a 10 gram per day increase in take the risk of cancer and cancer mortality decreased 4% and 7%, respectively.

A 2023 SR/AM found higher intake of nuts is associated with a decreased risk of several health conditions, and the dose-response analyses generally find most benefit is obtained when consuming 17-18 grams daily(Arnesen, 2023):

Reproduced from: Arnesen EK, Thorisdottir B, Bärebring L, Söderlund F, Nwaru BI, Spielau U, Dierkes J, Ramel A, Lamberg-Allardt C, Åkesson A. Nuts and seeds consumption and risk of cardiovascular disease, type 2 diabetes and their risk factors: a systematic review and meta-analysis. Food Nutr Res. 2023 Feb 14;67. doi: 10.29219/fnr.v67.8961. PMID: 36816545; PMCID: PMC9930735.

 

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 was further seen in a 2021 SR/network MA of RCTs, where other than an increase in waist circumference seen with hazelnuts, all other body size and composition outcomes improved with increased nut intake.(Fernández-Rodríguez, 2021b) This was particularly true for individuals with a BMI in the overweight or obesity range. A separate 2021 SR/MA of prospective cohort studies and RCTs also found no evidence of harm and some evidence of benefit for better anthropometric outcomes.(Nishi, 2021) Yet another 2021 SR/MA of RCTs extended these findings to individuals with T2DM, showing no impact of nut consumption on body weight or anthropometric outcomes.(Fernández-Rodríguez, 2021a)

This is likely due to a combination of the impact of nuts on satiety, decreased caloric consumption later in the day, and less caloric yield from nuts than would be expected by their fat content. Thus, whether you are or are not tracking calories, including nuts as a snack can be beneficial for weight management outcomes.

Specific nuts

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 (a more recent review on pistachios found no impact on inflammatory markers but a small benefit to systolic blood pressure)(Asbaghi, 2021). 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 highlighted the different phytonutrient profiles in the various types of nuts that may account for potential differences in health effects but also reaffirmed 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.

Recommendations

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

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 compositions of the oils help 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)

a figure showing the fatty acid content of different oils
Taken from Figure 1-2 of the 2015-2020 DGA

Considerations with olive oil

As one example, research has shown olive oil consumption to have several health benefits (see figure below regarding olive oil used in conjunction with a Mediterranean diet).(Jimenez-Lopez, 2020) 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 of the nutrients have been removed).(Foscolou, 2018) 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)

an image showing health benefits of olive oil
Reproduced from: Jimenez-Lopez C, Carpena M, Lourenço-Lopes C, Gallardo-Gomez M, Lorenzo JM, Barba FJ, Prieto MA, Simal-Gandara J. Bioactive Compounds and Quality of Extra Virgin Olive Oil. Foods. 2020 Jul 28;9(8):1014. doi: 10.3390/foods9081014. PMID: 32731481; PMCID: PMC7466243.

Of note, while lots of evidence shows olive oil has great health benefits, there is some research indicating canola oil may be even more beneficial, at least as it pertains to cholesterol levels.(Pourrajab, 2022)

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 or do less stringent quality control processing it may not be obvious to a typical consumer. Thus, many brands are adulterated in this fashion. This is actually a common problem worldwide.(Almoselhy, 2020; Casadei, 2021) There are certification programs worldwide for higher quality product. In the United States the California Olive Oil Council has a strict certification process. In the US I recommend when purchasing olive oil to get a brand with the “COOC” seal on it as that will likely be legitimate, assuming you want to ensure you purchase high quality product.

Unfortunately, I cannot find any literature comparing health benefits of pure extra virgin olive oil compared to adulterated formulations. Harmful effects certainly seem possible, but to what degree they exist seems very unclear.(Lozano-Castellón, 2022) My guess is that many trials use high quality product, but observational data that relies on real world consumption likely includes adulterated formulations to some degree. As the observational data is quite favorable towards health benefits of olive oil, it’s possible that even the adulterated products will contain enough olive oil to still impart health benefits, though this will likely depend on the degree of adulteration. Overall, I cannot provide an evidence-based recommendation regarding the importance of spending more money for the higher quality product.

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) When cooking above 200 degrees Celsius for extended periods of time (hours) this begin to generate modestly increased amounts of trans fatty acids, which contribute to poor health outcomes.(Bhat, 2022)

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 (this can be more expensive than other options) 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.

Recommendations

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.

Food preparation considerations

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; Maldonado-Pereira, 2018) From a safety standpoint it’s generally considered harmful to consumed oxidized cholesterol products.(Vicente, 2012; Hu, 2021) These tend to increase with prolonged cooking at higher temperatures, 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.

Distinct from cholesterol oxidation products, frying & cooking at high temperatures can also contribute to increased formation of advanced glycation end products.(Santos, 2021) These develop when glucose binds via non-enzymatic interactions to various substrates. This more readily occurs in the bloodstream in people with diabetes or insulin resistance and elevated blood glucose levels. With cooking, as an example, this can occur with the Maillard reaction where amino acids bond with glucose. This can be seen with french fries, barbecuing, cake, and other foods & cooking processes as well. In general, cooking at lower temperatures will help prevent these from developing.

Conclusion

I have now discussed the predominantly health-promoting aspects of grains, fruits & vegetables, and nuts & oils. 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. The greatest benefit is seen with intake levels of 1 serving daily (28 grams), but significant benefits can be seen with intake of half a serving daily.
  • Certain oils, such as olive oil, can have significant health-promoting properties. Cooking these with lower temperature settings and for shorter duration will help ensure the health benefits are maintained.

In the next lesson I will discuss the more controversial food groups including dairy, eggs, and meats.

Click here to proceed to Lesson 11

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