Lesson 13: An Overview of Various Diets

The idea is to eat foods that are predominantly “acid reducing” and to mostly avoid foods that are “acid producing”. Thus, this diet relies heavily on fruit, vegetables, seeds, nuts, legumes, and soy products, allows limited whole grains, and typically avoids eggs, meat & animal protein and processed foods. This diet may have merit for being mostly plant-based, but there are several rules that need to be followed and no research (to my knowledge) indicating superior health benefits relative to a vegetarian diet. Therefore, it does not make sense to me to follow this diet specifically. For people with chronic kidney disease, consider speaking with your healthcare provider about various dietary recommendations when it comes to dietary acid load.

A recent review discussed relevant pathways and speculative positive benefits of an alkaline diet.^{(Aoi, 2020)} At this point there is no strong evidence base suggesting an alkaline diet can be constructed to utilize these pathways to meaningfully influence health outcomes. The evidence that does suggest health-promoting benefits (such as a decreased risk of cancer^{(Bahrami, 2022)}) may be correlational instead of causative; for example, a low acid diet can be similar to the DASH diet discussed below.^{(Ostrowska, 2020)}

Dr. Weil has a website discussing this specific version of the anti-inflammatory diet. A couple of recent reviews have discussed anti-inflammatory diets; they mostly follow the healthy eating patterns discussed throughout this course.^{(Ricker, 2017; Norde, 2020)} This version of the diet will be health promoting, but the version indicated on Dr. Weil’s website advocates for preferentially consuming organic food (see Lesson 14 for a discussion about organic food) and multiple dietary supplements (not covered in this course but generally not necessary). Overall, this will be more complicated, costly, and difficult to adhere to than other viable diets that one could choose.

There is not one “Asian diet”, rather this is a conglomeration of dietary schemes typically seen across Asia. Typically, this diet includes daily vegetables/fruits/nuts/seeds/legumes/whole grains, less frequent dairy/eggs/poultry/healthy oils, and infrequent red meat/sugary desserts. The diet recommends six glasses of water or tea daily. Overall, this will be a generally healthy diet plan, though the infrequent dairy may make adequate calcium consumption more difficult, and one must be careful not to go overboard on rice/noodles as it can be easy to overeat these and enter an undesirable caloric surplus.  If curious, click here for more information.

This is essentially a low carbohydrate diet but not necessarily low enough to go into a state of ketosis for the duration of the diet. Phase 1 of the diet will likely yield ketosis but the diet allows progressively more carbohydrates as time goes on. Saturated fat intake may be excessive depending on your food choice. Additionally, when restricting carbohydrates you will miss out on having several servings of whole grains, and potentially specific fruits & vegetables, daily, all of which have health benefits. Multivitamin/mineral supplementation can be useful due to the restrictive nature of the diet.

You can expect rapid weight loss in the first few days when following the Atkins Diet, especially if exercising, due to depletion of glycogen stores (as this holds water in the body), and the comparative reviews above do indicate this is effective for weight loss. However, I generally do not recommend restrictive dieting practices, and restricting carbohydrates will limit the intake of many healthy nutrients. Thus, I generally do not recommend following the Atkins diet long term, though it should be safe if constructed optimally over a shorter time period (ie, months).

This diet emphasizes fruits, vegetables, whole grains, lean protein, and low-fat dairy. It discourages foods that are high in saturated fat as well as sugar-sweetened beverages and sweets. Sodium intake should not exceed 2,300 milligrams. For an overview of the DASH diet, see this 6 page PDF or this longer version. As indicated in the comparative reviews above there is ample evidence supporting the merits of this diet. If you do want to follow a named diet, the DASH diet is a very reasonable choice.

A 2021 SR/MA of 54 RCTs evaluating the DASH diet in patients with chronic diseases found^{(Lari, 2021)}:

• no impact on glycemic parameters
• a decrease in body weight (-1.59 kg), BMI (-0.64), and waist circumference (-1.93 cm)
• a decrease in total cholesterol (-5.12 mg/dL) and LDL (the “bad” type) cholesterol (-3.53 mg/dL) with no change in HDL cholesterol, VLDL cholesterol, or triglycerides
• a decrease in systolic blood pressure (-3.94 mmHg) and diastolic blood pressure (-2.44 mmHg)

A 2020 SR/MA of 17 prospective cohort studies evaluating the impact of the DASH diet on the risk of mortality in a dose-response manner found that for every 5 point increase in adherence to the DASH diet (on a scale of 8-40, with 40 being perfect adherence) there was a 5% decreased risk of all-cause mortality and a 3% decreased risk of CVD mortality, stroke mortality, and cancer mortality.^{(Soltani, 2020)} Nonlinear dose-response analysis showed that greater adherence led to a proportionally larger decrease in risk for all-cause mortality, cardiovascular mortality, and cancer mortality (there was not enough data to evaluate this for stroke mortality).

I discussed gluten and the merits, or lack thereof, of a gluten-free diet in Lesson 10. To summarize, a small percentage of the population (~1%) has Celiac disease and strongly benefits from following a gluten-free diet. A small percentage (<10%) of people may be sensitive to gluten or to compounds commonly found in gluten-containing foods (ie, FODMAPs), and these individuals may also benefit from a gluten-free diet as they will symptomatically improve when following one. Beyond this, there are no expected health benefits from following a gluten-free diet and it is otherwise needlessly restrictive and expensive.

This diet simply entails consuming mostly low GI foods (GI ≤ 55), smaller amounts of moderate GI foods (56 ≤ GI ≤ 69), and infrequent high GI foods (GI ≥ 70). I discussed the GI and the problems with using it as a marker of nutritional status in Lesson 6. In brief, while following this diet will be advantageous for avoiding significant amounts of non-nutritious calories (ie, regular cookies), there is no guarantee that you will obtain a fully nutritious diet by sticking to lower GI options. Additionally, high GI foods consumed in moderation with mixed meals generally do not cause undue harm to blood glucose status, though it makes more sense for individuals with insulin resistance or diabetes mellitus to avoid high GI foods, particularly in isolation. Practically, it is difficult to determine the GI of packaged foods or other foods that are not in online databases (ie, http://www.glycemicindex.com/). For these reasons, I do not recommend the glycemic-index diet.

The ketogenic diet has become extremely popular. It can be very difficult to adhere to as it typically requires <5% of your calories to come from carbohydrates for several weeks to enter a state of significant ketosis; during this process several negative side effects are typically experienced (in popular culture dubbed the “keto flu”^{(Bostock, 2020)}, this can include headache, fatigue, nausea, brain fog, dry mouth, constipation, weakness, and more that generally are most severe the first couple of weeks when following the diet and gradually subside).^{(Schutz, 2021)} One benefit is that it seems to suppress appetite, and for this reason it can be a great dieting tool.^{(Gibson, 2015; Roekenes, 2021)} People who do not lose weight may still have improvements in their waist circumference and triglycerides, though overall benefits are not as clear when there is no weight loss.^{(Lee, 2021)} There are other potential benefits as well, indicated in the figure below^{(Dowis, 2021)}:

However, it is also possible for your cholesterol and liver function tests to worsen while following a ketogenic diet, and for this reason anybody who chooses to follow one should likely get their labs checked 1-2 months after beginning it to see if they are negatively affected (ideally with pre-ketogenic diet labs already obtained to have a valid point of comparison).^{(Freire, 2020; Vargas, 2020; Houttu, 2023)}

Due to the limited carbohydrates there can be a lack of fruits, vegetables, and whole grains, thus limiting the health potential of this diet. This diet is effective for individuals with severe epilepsy, but other health benefits are more speculative in nature.^{(Ludwig, 2020)} Additionally, when in a caloric surplus it seems more difficult to gain skeletal muscle with resistance training when following a ketogenic diet.^{(Vargas, 2018)} While in a caloric deficit some data suggests it is difficult to maintain lean body mass on a ketogenic diet even when engaging in resistance training.^{(Ashtary-Larky, 2021)} , while other data suggests in physically active individuals that lean body mass is preserved when average protein intake is 1.7 grams/kilogram/day.^{(Coleman, 2021)} Following a ketogenic diet also seems counterproductive for endurance performance at high intensity that requires glycogen utilization.^{(Morena-Villaneuva, 2021)} Overall, I think it can be a useful tool for some people who are otherwise struggling with hunger in a caloric deficit, but otherwise I do not recommend a ketogenic diet.

For people who decide to use a ketogenic diet, I recommend only using this while actively losing weight, choosing healthy sources of fat (ie, sources with relatively little saturated fat), plugging your proposed diet into cronometer.com, and attempting to make substitutions to optimize the nutritional content for health if possible. Of interest, many of the appetite suppressing effects seem possible when consuming more carbohydrates than typically allotted (ie, up to 100 grams daily instead of the typical <50 gram threshold), which can allow greater intake of healthy food groups that are otherwise limited by their carbohydrate content.^{(Roekenes, 2021)} In fact, there is a “modified ketogenic diet” that typically includes macronutrient ratios of 82%/12%/6% for fat/protein/carbohydrate, which thus allows more carbohydrates than the standard ketogenic diet but still allows entry into a state of ketosis.

Additionally, it is important to ensure there are no safety concerns when starting a ketogenic diet. Recent guidance indicates this diet is either contraindicated or needs to be used very cautiously when^{(Watanabe, 2020)}:

• elderly, pregnant, or breastfeeding
• in people with type 1 diabetes mellitus, severe chronic kidney disease, severe heart failure, or with certain cardiac arrhythmias
• in people with solid tumors
• in people with certain rare genetic conditions (if you have a rare genetic condition it is generally advisable to always check with your healthcare provider (and more specifically your geneticist if you have one) prior to starting a new diet)

Other indications and contraindications are presented in the following table:

There are several variations of this diet, which is typically vegetarian or near-vegan and generally emphasizes carbohydrates that are low on the glycemic index. Usually this is a high-carbohydrate and low-fat diet. This diet emphasizes whole grains and vegetables, limits fruit/seeds/nuts/fish/seafood, and restricts other animal products/processed foods. Despite being high in carbohydrates, there is some evidence this can be helpful for diabetes.^{(Porrata-Maury, 2014)} However, due to the risk of deficiencies of certain nutrients such as vitamin B₁₂ and calcium, as well as the required food restrictions, I generally do not recommend a macrobiotic diet.

The Mediterranean diet largely conforms to the Dietary Guidelines for Americans, so much so that Table A3-5 describes how to follow this. As indicated in the comparative reviews above, there is ample evidence suggesting significant benefits from following the Mediterranean diet. One of the above reviews found the Mediterranean diet to have significant favorable evidence with no evidence of harmful effects, a finding not seen with any of the other examined diets.^{(Dinu, 2020)} If you do want to follow a named diet, the Mediterranean diet is a very reasonable choice.

Several recent reviews have evaluated the Mediterranean diet:

• A 2020 SR/MA evaluating the impact of the Mediterranean diet on endothelial function evaluated 14 RCTs with people of various health statuses and found that the Mediterranean diet improved endothelial function; overall flow-mediated dilation increased 1.66%.^{(Shannon, 2020)} The authors note that prior research indicates a 1% increase in flow-mediated dilation may correlate with a 13% decreased risk of cardiovascular events, and thus a 1.66% increase corresponds to a 22% reduction in risk.
• A 2020 SR/MA of 84 papers from 57 unique trials evaluating the impact of the Mediterranean diet on metabolic health found that compared to a control diet the Mediterranean diet led to^{(Papadaki, 2020)}:
  • a decrease in body weight (-1.72 kg), body mass index (-0.41), and waist circumference (-1.47 cm)
  • lower blood pressure (-1.34 mmHg systolic, -0.81 mmHg diastolic)
  • decreased glucose (-2.98 mg/dL) and insulin (-0.94 μU/mL)
  • lower total cholesterol (-5.70 mg/dL), LDL cholesterol (-8.24 mg/dL), triglycerides (-12.30 mg/dL), and higher HDL cholesterol (+1.30 mg/dL)
  • decreased inflammatory markers and markers of endothelial function
  • in only 2 studies each there was a 39% decrease in CVD incidence and a 33% decrease in stroke incidence
• A 2020 SR of 139 epidemiologic studies and intervention trials through 07/31/2019 described the evidence showing beneficial associations of the Mediterranean diet for mortality, CVD, various aspects of metabolic syndrome, diabetes, cancer, brain function, and mental health.^{(Sánchez-Sánchez, 2020)}
• A 2020 SR/MA including 117 studies evaluated the association of the Mediterranean diet with cancer and found that highest vs lowest adherence to the Mediterranean diet was associated with a 13% decreased risk of cancer mortality in cohort studies (not seen in 1 RCT), a 25% decreased risk of all-cause mortality among cancer survivors, and a decreased risk specifically for breast, colorectal, head & neck, bladder, gastric, liver, and respiratory cancer.^{(Morze, 2021)} Due to the epidemiologic nature of most of the evidence, the overall certainty was judged as moderate for cancer mortality & colorectal cancer and low or very low for the other cancer subtypes.
• A 2021 MA evaluating prospective cohort studies with 3.8-10.0 years follow-up on the impact of adherence to the Mediterranean Diet in individuals with CVD found that every 2 point increment in adherence was associated with a 15% decreased risk of all-cause mortality and a borderline significant 9% decreased risk of cardiovascular mortality.^{(Tang, 2021)}

Created as the “Mediterranean-DASH Intervention for Neurodegenerative Delay”, this attempts to combine the best aspects of the Mediterranean & DASH diets for brain health. Daily foods include 3 servings of whole grains, a salad & another vegetable, and if desired a glass of wine. You consume olive oil regularly, nuts on most days, a half cup of beans every other day, poultry & a half cup of berries at least twice weekly, and fish at least weekly. You mostly avoid red meats, butter, cheeses, sweets, and fried/fast food. For a detailed overview of the full scoring system, see table 1 here. Overall, this seems like a sensible diet plan, though the restriction on dairy can prove problematic for calcium intake. This was published for the first time in 2015 with observational data.^{(Morris, 2015)}

Further research shows:

• A 12-year Scottish cohort study found that adherence to the MIND diet is associated with decreased mortality (~12% decrease for each unit increase in MIND diet score) in a fully adjusted model.^{(Corley, 2020)}
• A 2021 SR of 13 articles (9 cohort studies, 3 cross-sectional studies, 1 RCT) found all of them demonstrated a beneficial impact on some aspect of cognition when following the MIND diet.^{(Kheirouri, 2021)}. The MIND diet yielded better outcomes relative to the Mediterranean, DASH, Pro-Vegetarian, and Baltic Sea diets. With only 1 RCT we need more research, but this is a promising diet for cognitive purposes.

This involves eating more fruits, vegetables, whole grains, and seafood, eating higher quality but less meat overall, seeking out more food from wild landscapes, using organic produce when possible, avoiding food additives, basing more meals on seasonal produce, consuming more home-cooked food, and producing less waste. Meals should aim for a 2:1 ratio of carbohydrates-to-protein. This is a very environmentally-friendly diet plan/philosophy.^{(Meltzer, 2019)} For that same reason, it can be fairly expensive and take a lot of time for food preparation. This diet should yield health benefits^{(Ramezani-Jolfaie, 2019)} but there is no indication this will yield better health outcomes than some of the easier alternatives you could from. For people with the time and money on their hands as well as the desire to best support the environment, this diet would be worth looking into more; otherwise there are easier options that are likely just as healthy.

Recent research shows:

• A 2020 SR/MA including 6 RCTs found that the Nordic diet could lead to small decreases in serum insulin (though this was not significant if one influential study was removed) and HOMA-IR (a measure of insulin resistance) with no impact on fasting blood glucose or other glycemic control markers.^{(Zimorovat, 2020)}
• A 2020 SR/MA of the impact of the Nordic diet on various health outcomes evaluated 13 prospective studies (all from European countries) and found when comparing the highest vs lowest adherence categories^{(Jalilpiran, 2020)}:
  • a 22% decreased risk of all-cause mortality and CVD mortality
  • a 14% lower risk of cancer mortality
  • a 20% lower risk of myocardial infarction, a 12% lower risk of stroke, and a 10% lower risk of type 2 diabetes
  • there was no association with colorectal cancer incidence
• A 2020 SR/MA of 7 RCTs evaluating the impact of the Nordic diet on weight loss found^{(Ramezani-Jolfaie, 2020)}:
  • two studies indicated a loss of body fat percentage compared to a control diet (-3.24% vs -1.45% and -2.1% vs -1.5%)
  • one of two studies found a significant decrease in body mass index compared to a control diet (-1.04)
  • one of three studies demonstrated a decrease in waist circumference relative to a control diet (-4.18 cm vs -1.32 cm)
  • in a MA of 5 RCTs there was greater weight loss with the Nordic diet relative to the control diets (-1.83 kg)

There are various ways to develop an Ornish diet, and there is evidence (initially published in 1990) that a strict version can at least partially reverse heart disease.^{(Ornish, 1990)} This strict version limits fat to 10% of your calories with very little of it being saturated, excludes almost all oils/caffeine, limits refined carbohydrates to 2 servings daily, limits dietary cholesterol (<10 mg daily), and excludes animal products other than egg whites & up to 2 servings of non-fat dairy daily. It emphasizes fiber and complex carbohydrates, and up to 1 serving of alcohol is permitted daily. This dietary plan also emphasizes exercise, stress management, and relationships. Overall, this is a heart-healthy diet but can be very difficult to adhere to due to the significant fat restriction. If curious, click here for more information.

This diet is based on the notion that we should eat what we typically consumed throughout our evolutionary history, though one could question how confidently we know what humans consumed thousands of years ago. Nonetheless, this forbids refined sugar, dairy, grains, legumes, and alcohol. Nutrition mostly consists of fruits, vegetables, poultry, fish, meat, eggs, nuts & seeds (but not peanuts or peanut butter as peanuts are technically a legume). Thus, this diet omits multiple healthy food groups and if care is not taken you may consume excess saturated fat.

Research evaluating this diet does show health benefits (see below), however trials are typically small and a larger body of research is needed. If someone wants to follow this there are many recipes available online, and I would suggest being careful to avoid micronutrient deficiencies (always feel free to plug your diet into cronometer.com to see if you are deficient in anything) and excessive saturated fat intake. Nonetheless, I generally do not recommend a Paleolithic diet due to the restrictive nature and lack of some healthy food groups (ie, whole grains).

Some recent review articles:

• A 2019 SR/MA of 8 RCTs found the paleolithic diet led to weight loss (-1.68 kg), a decrease in body fat percentage (-1.31%), a decrease in blood pressure (-4.75 mmHg/-3.23 mmHg for systolic/diastolic, respectively) and various lipid and inflammatory markers.^{(Ghaedi, 2019 – a corrected version was published in 2020)}
• A 2019 SR/MA of 11 RCTs found that the paleolithic diet led to a decrease in body weight of -3.52 kg, body mass index of -1.09, and waist circumference of -2.46 cm.^{(de Menezes, 2019)}
• A 2021 SR/MA of 10 RCTs involving patients with overweight/obesity or other metabolic disorders found that the paleolithic diet led to improvements in insulin and insulin resistance, total/HDL/LDL cholesterol, triglycerides, systolic and diastolic blood pressure, and c-reactive protein.^{(Sohouli, 2021)}
• A 2021 SR/MA found that the paleolithic diet led to many health benefits even when consumed in ad libitum fashion; perhaps due to the high satiety of the diet significant weight was lost anyway.^{(Frączek, 2021)} It’s unclear to what degree the various cardiometabolic improvements were secondary to weight loss compared to the health benefits of the diet. There were no studies done in athletes, and the authors discuss that it is unclear if the Paleo diet has merits for athletic populations.

This diet advocates eating foods in the raw form without cooking at any temperature >115 degrees Fahrenheit and without processing, microwaving, irradiation, genetic engineering, or exposing the food to pesticides or herbicides. Common food items will include fresh fruits/vegetables, nuts/seeds, uncooked grains, dried organic legumes, and extra-virgin olive oil. Some people will also consume raw animal products (ie, uncooked eggs, raw milk, raw meat). It can be expensive to obtain appliances to prepare food for this diet and organic ingredients are generally considerably more costly than non-organic. The risk of food poisoning increases significantly on this diet, and many people consume inadequate calories to meet nutritional needs when following this. You must be careful to ensure sufficient calcium, vitamin B₁₂, and vitamin D intake.

Overall, this diet is extremely restrictive, difficult to follow, potentially unsafe due to concerns of food poisoning, and may be nutritionally inadequate depending on what you include. For these reasons I do not recommend the raw food diet.

Created by the National Institute of Health’s National Cholesterol Education Program, this includes ≥6 servings of grains daily, 3-5 servings of vegetables/dry beans/peas, 2-4 servings of fruits, 2-3 servings of fat-free or low-fat dairy, up to 2 egg yolks weekly, up to 5 ounces of meat daily (preferentially fish and skin-off poultry), and canola/olive oil. This diet sets calorie goals based on gender if there is a desire for weight loss, limits saturated fat to 7% of daily calories, and limits dietary cholesterol to 200 milligrams daily. After 6 weeks if LDL cholesterol has not dropped by 8% you should add 2 grams of plant stanols or sterols & 10-25 grams of soluble fiber daily. If curious, click here for a full overview. This is theoretically a healthy diet plan, and it can decrease cholesterol.^{(Lichtenstein, 2002)} However, there have been few large/prolonged trials, if any, evaluating the TLC diet. Overall, this is a reasonable dietary plan though it will require care to ensure you do not exceed the saturated fat or cholesterol limits.

Due to the exclusion of many different foods and food products, planning a fully nutritious vegan diet takes care. It can be easy to consume inadequate amounts of calcium, vitamin D, vitamin B₁₂, zinc, omega-3 fatty acids, iron, and protein. Due to the very restrictive nature and the likelihood of nutritional deficiencies without careful planning, as well as little evidence of significant benefit compared to other diets listed here, I do not recommend a vegan diet for health purposes.

However, for people who wish to follow a vegan diet for ethical, environmental, or personal reasons, it will be important to do so as healthily as possible. Plugging your diet into cronometer.com, taking supplements when needed, and discussing this with your healthcare provider are steps you can take to help ensure you do this healthily. Many evidence-based tips are available online at websites such as https://www.veganhealth.org, and the Academy of Nutrition and Dietetics put out a position statement in 2016 advising how to consume both vegetarian and vegan diets in a healthy manner.^{(Melina, 2016)}

Recent reviews:

• A 2021 SR evaluating the relationship of vegan diets with cardiovascular health outcomes overall found no consistent benefit or harm relative to control diets.^{(Kaiser, 2021)}
• A 2021 SR evaluating 48 studies regarding if vegan diets meet nutrition requirements found that^{(Bakaloudi, 2021)}:
  • energy intake is normally adequate
  • macronutrient intake is normally adequate though protein may be slightly low
  • iron intake is increased but it is less bioavailable so ferritin (the storage form of iron) levels are on the lower side
  • vitamins A/B₁/B₆/C/E, copper, folate, magnesium, phosphorus, potassium, and sodium are adequately consumed while selenium and zinc are consumed in lesser amounts but likely not to the point of having low blood levels
  • there are more frequently low intakes of vitamins B₂/B₃/B₁₂/D, calcium, and iodine

If done appropriately a vegetarian diet is a healthy option, as indicated in Tables A3-3 and A3-4 in the Dietary Guidelines for Americans. A MyPlate equivalent with guidelines has even been created for children.^{(Baroni, 2019)} However, depending on food choices this may not yield great health benefits; for example, you could choose to mostly consume refined grains & sugary/fatty products. When done in such a way as to meet the dietary guidelines this should overall be a very healthy diet (see relevant review articles below) and should be environmentally friendly as well.^{(Fresán, 2019; Keaver, 2021)} Thus, for individuals willing to give up meat, a well-designed vegetarian diet is a great option to consider.

Some recent review articles:

• A 2020 SR/MA of 15 trials found vegetarian diets compared to control diets led to a decrease in systolic blood pressure by -2.66 mmHg and diastolic blood pressure by -1.69 mmHg, with larger impacts seen with vegan diets.^{(Lee, 2020)} Most of the trials did not consider changes in energy consumption and body weight.
• A 2020 umbrella review of SR/MAs of the health outcomes associated with vegetarian diets found^{(Oussalah, 2020)}:
  • significant decreases in total cholesterol (-21.2 mg/dL), LDL cholesterol (-18.1 mg/dL), a small decrease in HDL cholesterol (-3.2 mg/dL), and no impact on triglycerides
  • a higher risk of vitamin B₁₂ deficiency as well as elevated homocysteine (low vitamin B₁₂ levels cause increases in homocysteine), decreased zinc and ferritin (a storage form of iron) levels (it’s not stated if these are pathologically low)
  • 4% decreased bone mineral density
  • observational studies show a decreased body mass index of -1.49 in vegetarians compare to omnivores and interventional studies show a loss in body weight of 3.4-4.6 kg when adopting a vegetarian diet
  • no influence on c-reactive protein (a measure of inflammation)
  • decreased odds of diabetes (0.73) and a significantly lower blood glucose level (-5.08 mg/dL)
  • a 29% decreased risk of heart disease
  • lower blood pressure in observational studies (-6.9 mmHg systolic/-4.7 mmHg diastolic) and interventional studies (-4.8 mmHg systolic/-2.2 mmHg diastolic)
  • an 8-18% lower risk of cancer, though with no specific decreased risk in a more recent analysis of breast, colorectal, or prostate cancer
  • no overall impact on all-cause mortality
  • an overall 11% decreased risk of 16 pooled negative health outcomes
• A 2020 SR demonstrated an association between vegetarian diets and eating disorder pathology, at least in adolescents and young adults.^{(Sergentanis, 2020)} While this has not been found to be a causal relationship, and evidence indicates eating disorder pathology would typically precede the adoption of this diet, for the healthcare providers reading this you can keep this association in the back of your mind when working with people who adopt vegetarian diets.
• A 2021 SR/MA of various plant-based diets found an association with decreased all-cause mortality and coronary heart disease mortality.^{(Jafari, 2021)} The authors attempted to determine the impact of different plant-based diet types (ie, healthy vs unhealthy based on diet quality) but found too few studies to draw any confident conclusions regarding the subtypes.
• A 2021 SR evaluating the influence of vegetarian diets on physical performance included 15 studies.^{(Araújo, 2021)} Only 1 study showed a negative effect and in that study the vegetarian diet group had lower caloric intake. Eight studies found a benefit in the vegetarian diet group (possibly due to higher carbohydrate intake or better health effects (ie, greater visceral fat loss was seen in one study with patients with diabetes)) and 9 found no difference (some of these included creatine supplementation, a substance that helps with energy production over short time intervals (ie, sprinting or lifting heavy weights) and is typically found in meat products).
• A 2022 SR/MA including 16 cohort studies found there was an association with following a vegetarian diet and increased odds of depression (53% higher odds based on results from 6 studies), but there was no increase in depression score, some studies showed no association or even an inverse association, and many studies did not in any way control for the reason why many people chose to follow a vegetarian diet.^{(Fazelian, 2022)} Thus, while an association was seen, there is no indication that the vegetarian diets caused the onset of depression.

The idea of this diet is to eat meals with 40% carbohydrates, 30% protein, and 30% fat, and to keep your insulin and inflammation-promoting hormones in a healthy zone (of note, I am not aware of any evidence suggesting this is a valid concept). The diet limits calories to 1,200 & 1,500 for women & men daily, respectively. There are 3 meals & 2 snacks daily. You should consume breakfast within 1 hour of waking & should not go more than 5 hours without eating (except overnight). This diet encourages low glycemic index carbohydrates, protein from skinless chicken/turkey/fish/egg whites/low-fat dairy/tofu/soy meat substitutes, and plant-based fat options such as nuts & olive oil.

Due to the very regimented approach, it takes a lot of planning and effort to stick to the Zone diet, and as indicated in the comparative literature above there is no evidence suggesting this will generate health benefits superior to other dietary approaches. Thus, I do not recommend following the Zone diet.