How Flexitarian and Plant Diets Impact Your Health and Biomarkers

By Neel Duggal, August 18, 2015


Are you a die-hard vegetarian looking to convince your omnivorous friends to follow your path? Or someone who wants to cut down on meat, but not forsake your weekly chipotle chicken burrito forever?

Vegetarian diets, which eliminate meat consumption, and “flexitarian” diets, which minimize it, are rapidly growing in popularity. Below we document some of the potential health benefits you gain by reducing or cutting out meat from your diet. Then we examine key biomarkers to monitor so you can optimize your low-to-no meat diet for overall health and peak performance.

How do we classify the variations on low-meat and no-meat diets? Vegetarians do not eat meat, fish, and poultry. Some, called “lacto-ovo vegetarians,” eat eggs and dairy. According to “Vegetarianism in America,” a recent study published by Vegetarian Times, 7.3 million people follow vegetarian diets including elite athletes such as NFL Hall of Famer Joe Namath and baseball player Prince Fielder.1 Vegans are vegetarians who abstain from consuming any animal products—including eggs, all dairy, and even honey. About one million Americans are vegans.

While increasing numbers of Americans are eliminating meat, many more are serious about minimizing it. Many people who eat meat are eating less of it in modified diets called “flexitarian” or “vegetarian-inclined.” Some, such as pescetarians and certain paleo diet enthusiasts, eat fish but not meat or poultry. Many flexitarians eat all forms of meat but less of it compared to the standard Western diet.

Overall, about 22.8 million people in the US follow a vegetarian-inclined diet, over three times the amount of people who are strictly vegetarian.1 Additionally, many Americans participate in the popular “Meatless Mondays,” an initiative by the Johns Hopkins Bloomberg School of Public Health that promotes foregoing meat consumption on (you guessed it) Mondays.


Many people argue that the less extreme alternative of reducing meat consumption is easier for people to adopt than eliminating meat altogether. In a large survey conducted by the advocacy group Humane Research Council, 84% of vegetarians and vegans resume eating meat after attempting to abandon it. 2 About 43 % of these former vegetarians said they had considerable difficulty “sticking to a pure diet,” indicating that the all-or-nothing approach of eliminating meat is not sustainable. 2 This data is corroborated by personal opinions: the Dalai Lama says he just couldn’t go all-or-nothing with meat and eats a low-meat, flexitarian diet. And while I like vegetarian and vegan foods, I am not sure if I can forsake salmon kebabs for the rest of my life.

The most commonly cited reason why people pursue a vegetarian or meat-minimal diet is for their health, not the environment or ethics. 2 However, does science support the commonly held notion that a vegetarian diet is better for you?

What Are the Health Benefits of Cutting Back on Meat?

Research shows that people who subscribe to a no-meat, vegetarian diet experience better weight maintenance. In a meta-analysis of twelve random controlled trials involving 1151 subjects, researchers observed the effects of a vegetarian diet intervention on previously non-vegetarian subjects. On average, the interventions lasted 18 weeks. After controlling for key demographic factors, the researchers observed that subjects assigned to vegetarian interventions lost 2.02 kg (4.45 lb) more weight than individuals assigned to a non-vegetarian diet. These differences were more pronounced for vegans, who lost an average of 2.52 kg (5.56 lb), and less pronounced for lacto-ovo vegetarians, who shed an average of 1.48 kg (3.26 lb). 3 Researchers concluded that “vegetarian diets appear to have significant benefits on weight reduction compared to non-vegetarian diets.” 3


Vegetarians are also less predisposed towards heart-related diseases. In a cross-sectional analysis of 773 subjects, researchers examined the relationship between vegetarian diets and metabolic risk factors (MRFs) over a five-year span. MRFs are a group of five indicators that predict the risk of cardiovascular illnesses including heart disease, stroke, and diabetes.

Three of these five MRFs—HDL cholesterol, triglycerides, and glucose—are biomarkers measured by InsideTracker’s blood analysis. Increased levels of triglycerides and glucose and decreased levels of HDL cholesterol increase the risk of cardiovascular disease. The other MRFs are blood pressure and waist circumference.

Researchers observed that triglycerides in vegetarians decreased on average 9 mg/dL, glucose decreased on average 6 mg/dL, and HDL cholesterol increased about 1 mg/dL. 4 In contrast, triglycerides in non-vegetarians increased on average 8 mg/dL, glucose increased on average 4 mg/dL, and HDL cholesterol decreased on average 0.5 mg/dL. 

These results indicate that vegetarian diets have a more favorable impact on metabolic biomarkers than non-vegetarian ones. The researchers also noted that “The relationship persists after adjusting for lifestyle and demographic factors.” 4 Thus, people who consume a meat-free diet are more likely to have optimized metabolic biomarkers such as cholesterol, triglycerides, and glucose.


Key Takeaways: A no-meat vegetarian diet is a healthy lifestyle choice that may produce notable heart-healthy benefits and weight loss.

Recommendations: If you are pursuing a vegetarian diet, add foods containing high-quality vegetable proteins, important nutrients, and fiber. Use InsideTracker’s Recommendation Engine to learn what is optimal for you based on your internal biochemistry.

Is Flexitarian Good Enough?

However, if you are like the Dalai Lama and me and can’t forego meat entirely, all is not lost. Flexitarians experience similar health benefits.

In a large cross-sectional study, scientists asked 55,459 healthy Swedish women about their meat-eating habits. Of these, 54,257 identified themselves as omnivores, 960 as semi-vegetarians, 159 as lactovegetarians, and 83 as vegans. Researchers noted that “the prevalence of overweight or obesity (BMI > 25) was 40% among omnivores, 29% among semi-vegetarians and vegans, and 25% among lactovegetarians.” 5. The authors concluded that “The advice to consume more plant foods, and fewer animal products may help individuals control their weight.” 5


Healthy, low-meat diets have similar cardio-protective benefits as meatless ones. In a randomized clinical trial from the Stanford University Medical Center, researchers provided 120 generally healthy adults, ages 30 to 65, with two different diets.

  • The first diet, called the Low-Fat diet, was a standard US diet with low levels of fat and normal levels of meat.
  • The second diet, called the Low-Fat Plus diet, contained considerably more plant-based proteins from legumes, whole grains, and vegetables, and much less meat. Both Low-Fat diets had equal levels of calories, macronutrients such as proteins, fats, and carbohydrates, and micronutrients such as iron.

After only four weeks, the researchers observed that the subjects who had received the Low-Fat Plus diet experienced twice the reduction in total cholesterol and LDL cholesterol (the bad cholesterol) compared to those who consumed the Low-Fat diet with meat. [6]

The researchers also noticed no significant differences in triglycerides and HDL cholesterol between the two groups.6 The researchers emphasized the importance of “nutrient-dense plant-based foods” in optimizing your cholesterol profile for cardiovascular health and athletic performance.6


Additionally, people who consume the low-meat Mediterranean diet experience benefits in heart health. The modern Mediterranean diet emphasizes plant-based foods such as whole grains, nuts, legumes, fruits, and vegetables alongside healthy fats such as olive oil. The diet also recommends consuming primarily lean meats such as fish and poultry and reducing overall meat consumption—especially red meat.

In a cross-sectional study of 780 career male firefighters ages 18 and older, researchers asked subjects the key characteristics of their diet and tracked them for five years. They observed that firefighters with a “greater adherence to a Mediterranean-style dietary pattern had significant inverse associations with metabolic syndrome, LDL-cholesterol and reported weight gain.” 7 Additionally, the scientists noted a significant increase in heart-healthy HDL-cholesterol. 7

Key Takeaways: If you feel that totally eliminating meat is too extreme, try a reduced-meat flexitarian diet such as the Mediterranean diet. Compared with higher meat diets, well-planned flexitarian diets yield numerous health benefits such as shedding body fat, lowering levels of LDL cholesterol, and maintaining overall health.

Recommendation: Consider eating less overall meat and adding more vegetable-based proteins such as lentils and quinoa to your diet. Use InsideTracker to find out which foods are best for your diet and to make sure that your lipid biomarkers are in the optimal zones.

If I Minimize Meat, Which Biomarkers Do I Need to Look out for?

Given the substantial health benefits of vegetarian and flexitarian diets, you need to monitor some biomarkers. Meat is a source of many key vitamins, minerals, and macronutrients. If you cut down or cut out meat, you may be at increased risk for numerous biomarker deficiencies.

To extract the heart-related benefits of these diets, you must regularly monitor your biomarkers using InsideTracker blood analysis and modify your diet as needed. Below is research on key nutrients and hormones you should pay attention to. Then we provide sample InsideTracker recommendations to optimize your biomarkers, even for the strictest vegans and most elite athletes.


The biomarker iron plays an integral role in many physiological processes. It is the key component of hemoglobin—the protein in red blood cells that transports oxygen to different tissues in the body—and myoglobin, the protein in muscles that binds to oxygen. Iron is also involved in the conversion of blood sugar, an especially crucial process for athletes.  

Unfortunately, only 46% of our users have optimal iron levels. A full 44% have suboptimal iron for their given demographics and lifestyle, which can lead to unwanted symptoms such as fatigue and weakness, and potentially result in long-term impairment of muscle and heart function. 8 On the flip side, 10% of users have iron above their optimal zones, which can lead to toxicity in the body.

Because meat and seafood have the highest amount of readily absorbable iron (“heme iron”), vegetarians and people who eat low amounts of meat are more likely to suffer from nutrient deficiency. 9 How can you avoid this? In a recent study, researchers surveyed 107 women about their nutritional lifestyle patterns and serum iron levels. They concluded “educating non-vegetarians about the benefits of increased flesh food consumption and vegetarians about dietary iron enhancers and inhibitors may have potential for addressing the high rates of iron deficiency among young women.” 10

By extension, the most important way to deal with iron deficiency is to proactively monitor your status and modify your vegetarian/flexitarian diet with good recommendations. Regular monitoring will also help you avoid potential excess iron levels.

Key Takeaways: Because many meat sources are abundant in iron, people who consume little to no meat should regularly monitor their iron status to make sure that they have optimal levels.

Recommendations: If you’re a flexitarian who tests low for iron, consider incorporating shellfish or chicken liver to your diet. Iron-deficient vegans and vegetarians can eat cooked soybeans, blackstrap molasses, cooked lentils, and iron supplements. Also, check out our recommendation engine and blog The Myth of the Nutrition Facts Label—Iron Absorption Debunked to get more detailed information on how maximizing iron absorption.

Sex Hormone Binding Globulin (SHBG)

Sex hormone binding globulin (SHBG) is a glycoprotein produced in the liver that binds to testosterone (and other sex hormones) and transports them through the bloodstream. When testosterone is attached to SHBG, it does not exert its typical effects. Testosterone is “bound” when attached to SHBG and “free” when it is not; the sum is “total testosterone.”

High SHBG is an issue for people such as men and athletes who need a lot of free testosterone. In men, elevated SHBG levels are associated with erectile dysfunction, lower libido, and infertility. In both sexes, low testosterone can impair workout recovery and reduce muscle growth. Furthermore, elevated SHBG may decrease the amount of free estrogen in the blood, reducing bone mass and potentially leading to osteoporosis.

Vegetarians are more likely to suffer from elevated levels of SHBG than non-vegetarians. In a 2009 research study, researchers recruited 21 healthy middle-aged omnivore women and 19 healthy vegetarian/vegan middle-aged women for a year-long study. Researchers had the women participate in 1-3 hours of exercise per week and made sure they consumed equal amounts of protein. At the end of the study, scientists observed equal similar levels of total testosterone in the omnivores (1.76 nmol/L) and vegetarians (1.79 nmol/L). 11

In contrast, the vegetarians had 50% higher SHBG than the omnivores (46 nmol/L vs. 69 nmol/L). 11 These findings suggest that a vegetarian-based diet high in protein substantially increases SHBG without changing total testosterone, thus leading to a potential decrease in free testosterone.


That being said, healthy levels of SHBG are easily accomplished through a vegetarian diet. First, you need to evaluate your SHBG levels, given your specific lifestyle and demographics, with an InsideTracker analysis. Then you can use a research-backed intervention, such as increasing healthy calories, to decrease elevated SHBG levels. 12 Additionally, make sure that your SHBG doesn’t dip too low. SHBG has many physiological functions in the body, and low levels are associated with cardiovascular problems such as heart disease and type 2 diabetes.13

Key Takeaways: Unhealthily elevated levels of SHBG can impair athletic performance and lead to imbalances in the body. Vegetarians are more likely to have high SHBG and thus lower free testosterone.

Recommendations: Use a research-backed intervention to decrease SHBG, such as increasing healthy calorie intake. Additionally, make sure that your SHBG levels don’t dip too low. That can lead to a different set of health problems.

Vitamin B12

Vitamin B12, also known as “cobalamin,” is a water-soluble vitamin. It plays key roles in forming blood cells and maintaining optimal function of the brain and nervous system. Vitamin B12 deficiency can lead to fatigue and difficulty walking. If left untreated, it can progress to hallucinations, memory loss, and anemia. 14

Vegetarians and flexitarians are more likely to suffer from vitamin B12 deficiency than meat-eaters. 14 This is because vitamin B12 is mostly found in animal foods such as poultry, fish, meat, eggs, and dairy. A 2009 cross-sectional study from Slovakia examined vitamin B12 status in lacto-ovo vegetarians vs. omnivores. Research discovered that omnivores had average vitamin B12 levels of 302 pmol/L and vitamin B12 deficiency 28% of the time. In contrast, lacto-ovo vegetarians had average vitamin B12 levels of 246 pmol/L and were deficient 47% of the time. 15


Thus, people who consume a low-to-no meat diet should either take vitamin B12 supplements or find vegetarian foods fortified with B12. 15 Just like with iron and zinc, you want to monitor regularly so you stay in the optimal zone for vitamin B12. We typically see 31% of users above that zone, and therefore at risk for excess vitamin B12. Additionally, some natural medicine practitioners claim that vitamin B12 supplements can be used to treat Alzheimer’s. While adequate levels of vitamin B12 help prevent cognitive decline, this claim is not backed up by science.

Key Takeaways: If untreated, vitamin B12 deficiency can lead to serious side effects. Flexitarians and vegetarians should closely monitor their vitamin B12 using blood analysis and adjust their diet if needed.

Recommendations: If you are cutting down on meat, remember to eat food high in vitamin B12 such as lean cuts of beef, poultry, or eggs. If you are going vegetarian or vegan, try fortified soy milk, almond milk, and vitamin B12 supplements to get your necessary levels.

Vitamin D

It is well-established that vitamin D is a nutrient that helps maintain bone health and the body’s ability to absorb minerals such as calcium and magnesium. 16, 17 Recent research suggests that vitamin D plays a crucial role in stimulating muscle growth, increasing explosive power, and slashing excess body fat. 18, 19


Vitamin D is naturally found only in a few foods. As a result, vitamin D deficiency is prevalent in the general population. Only 12% of our users have optimized levels. People who eat a meat-restricted diet tend to have lower blood concentrations of vitamin D. According to recent research, the average vitamin D blood concentrations in non-vegetarians, pescatarians, lacto-ovo vegetarians, and vegans are respectively 30.6 ng/mL, 29.8 ng/mL, 26.8 ng/mL, and 22.4 ng/mL. 20 This data puts vegetarians and vegans at a higher risk of having sub-optimal levels of vitamin D.


If you are eating a meat-restricted diet, the best way to get vitamin D is taking supplements, eating mushrooms, and/or increasing exposure to sunshine. Non-vegans can also consume dairy products fortified with vitamin D and low-meat eaters can eat fatty fish such as sardines.

Key Takeaways: Vitamin D is a nutrient with a variety of roles in the body. Because some vitamin D sources are in meat, those who cut down on meat or eliminate it altogether typically have lower levels.

Recommendation: Get a blood analysis to see if you’re deficient in vitamin D. Then see which recommendations are best suited for your diet.

Cutting Through the Meat: The Importance of Monitoring and Modifying

Both flexitarian and vegetarian regimens have health, ethical, and environmental merits. A strategic meat-minimal diet can help you lose weight, reduce the risk of cardiovascular illness, and avoid un-optimal levels of biomarkers such as iron and zinc. Even for elite athletes such as Prince Fielder, “well-planned, appropriately supplemented vegetarian diets appear to effectively support athletic performance.” 21 At the end of the day, we want you to choose a diet based on YOUR internal biochemistry and personal ethics. We’ll provide you with the algorithms, technologies, and tools you can utilize to minimize meat and maximize your health.


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List of References

1. Vegetarian Research Group, Vegetarian Times, Harris Interactive Service Bureau.

2. Asher, Kathryn, Che Green, and Dr. Hans Gutbrod. Study of Current and Former Vegetarians and Vegans. Rep. Humane Research Council, Dec. 2014. Web. 13 July 2015.

3. Huang, Ru-Yi, et al. "Vegetarian Diets and Weight Reduction: a Meta-Analysis of Randomized Controlled Trials." Journal of General Internal Medicine (2015): 1-8.

4. Rizzo, Nico S., et al. "Vegetarian Dietary Patterns Are Associated With a Lower Risk of Metabolic Syndrome: The Adventist Health Study 2." Diabetes Care 34.5 (2011): 1225-1227.

5. Newby, P. K., Katherine L. Tucker, and Alicja Wolk. "Risk of overweight and obesity among semivegetarian, lactovegetarian, and vegan women." The American Journal of Clinical Nutrition 81.6 (2005): 1267-1274.

6. Gardner, Christopher D., et al. "The effect of a plant-based diet on plasma lipids in hypercholesterolemic adults: a randomized trial." Annals of Internal Medicine 142.9 (2005): 725-733.

7. Sleiman, Dana, Marwa R. Al-Badri, and Sami T. Azar. "Effect of Mediterranean Diet in Diabetes Control and Cardiovascular Risk Modification: A Systematic Review." Frontiers in Public Health 3 (2015).

8. Arezes, J., and E. Nemeth. "Hepcidin and iron disorders: new biology and clinical approaches." International Journal of Laboratory Hematology 37.S1 (2015): 92-98.

9. Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc: a Report of the Panel on Microtnutrients. Washington, DC: National Academy Press, 2001.

10. Leonard, Alecia J., et al. "The effect of nutrition knowledge and dietary iron intake on iron status in young women." Appetite 81 (2014): 225-231.

11. Aubertin-Leheudre, Mylene, and Herman Adlercreutz. "Relationship between animal protein intake and muscle mass index in healthy women." British Journal of Nutrition 102.12 (2009): 1803-1810.

12. Campbell, Kristin L., et al. "Reduced-calorie dietary weight loss, exercise, and sex hormones in postmenopausal women: randomized controlled trial." Journal of Clinical Oncology (2012): JCO-2011.

13. Calderon-Margalit R., S.M. Schwartz, M.F. Wellons, , et. al. Prospective association of serum androgens and sex hormone-binding globulin with subclinical cardiovascular disease in young adult women: the “Coronary Artery Risk Development in Young Adults” women’s study. J Clin Endocrinol Metab. 2010 Sep 95(9):4424-31.

14. Woo, Kam S., Timothy C.Y. Kwok, and David S. Celermajer. "Vegan diet, subnormal vitamin B-12 status and cardiovascular health." Nutrients 6.8 (2014): 3259-3273.

15. Krivošíková, Zora, et. al. "The association between high plasma homocysteine levels and lower bone mineral density in Slovak women: the impact of vegetarian diet." European Journal of Nutrition 49.3 (2010): 147-153.

16. Horsley, Tanya, et. al. Effectiveness and safety of vitamin D in relation to bone health. US Department of Health and Human Services, Public Health Service, Agency for Healthcare Research and Quality, 2007.

17. Ross, A. Catharine, et. al. "The 2011 report on dietary reference intakes for calcium and vitamin D from the Institute of Medicine: what clinicians need to know." The Journal of Clinical Endocrinology & Metabolism 96.1 (2011): 53-58.

18. Wyon, Matthew A., et. al. "The influence of winter vitamin D supplementation on muscle function and injury occurrence in elite ballet dancers: A controlled study." Journal of Science and Medicine in Sport 17.1 (2014): 8-12.

19. Forney, Laura A., et al. "Vitamin D Status, Body Composition, and Fitness Measures in College-Aged Students." The Journal of Strength & Conditioning Research 28.3 (2014): 814-824.

20. Crowe, F.L., M. Steur, N.E. Allen, P.N. Appleby, R.C.Travis, T.J. Key. "Plasma concentrations of 25-hydroxyvitamin D in meat eaters, fish eaters, vegetarians and vegans: results from the EPIC-Oxford study. " Public Health Nutr. 2011 Feb; 14(2):340-6.

21. Barr, Susan I., and Candice A. Rideout. "Nutritional considerations for vegetarian athletes." Nutrition 20.7 (2004): 696-703.


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