It’s been quiet on this website for a long time while I’ve had my attention on several all-consuming projects. One was the new edition of Vegan for Life. By the time that book was published last May, I was already immersed in an even bigger endeavor which was a 10-year update to The Dietitian’s Guide to Vegetarian Diets, scheduled for publication in October 2021. Co-authored with Dr. Reed Mangels and Dr. Mark Messina, this is a textbook and a comprehensive overview of all aspects of vegan and vegetarian nutrition.
One subject that both books cover is the use of vegan diets for reducing risk for chronic disease, losing weight, or managing heart disease or diabetes. Defining the “best” vegan diet for these purposes isn’t easy. As with just about any topic in nutrition, the research is often conflicting and uncertain.
Among many vegans, there is a prevailing belief that a low-fat, whole foods vegan diet is the standard for healthy eating. Several studies, primarily from the same group of researchers, have associated this diet with weight loss and improvements in blood glucose control and risk factors for heart disease. 1-7 These studies generally use a restrictive version of a vegan diet, eliminating not just animal foods but also encouraging avoidance of nuts, seeds, avocados, and added fats. It’s an effective approach for weight loss for some people, especially in the short term. By emphasizing foods with low energy density, low-fat diets allow consumption of a greater volume of foods sometimes leading to an automatic reduction in calorie intake.8 It’s also possible that dietary monotony through restriction of whole categories of foods (any foods) is associated with lower calorie intake.9
But for a number of reasons, a very low-fat vegan diet may not be the ideal choice for managing chronic disease, reducing risk for heart disease, or even for weight loss.
Low-Fat Vegan Diets Eliminate Heart-Healthy Foods
Although low-fat vegan diets result in reduced blood cholesterol levels and improved insulin sensitivity, this is most likely a result of weight loss, not the absence of fat-rich foods.3 For one thing, the cholesterol-lowering aspects of low-fat vegan plans – higher fiber and low saturated fat content—aren’t unique to these diets. High-fat vegan diets like the Eco-Atkins pattern are also low in saturated fat and rich in fiber and are effective in lowering LDL-cholesterol and improving insulin sensitivity.10 Most high-fat plant foods are rich in unsaturated fats (the exceptions are coconut and palm oils) which lower LDL-cholesterol when they replace saturated fat in the diet. Higher-fat foods like nuts11,12 and perhaps soy foods13,14 have benefits for reducing heart disease risk that appear to go beyond their effects on blood cholesterol levels. Diets rich in monounsaturated fat may also be beneficial for glucose control in some people with diabetes.15,16 In terms of heart health, there are no benefits to eliminating these foods from your diet.
Low-Fat Diets May Lack the Essential Omega-3 Fatty Acid
You don’t have to pile on fat-rich foods to meet needs for the essential omega-3 fat alpha-linolenic acid (ALA). Just a tablespoon of ground flaxseed, providing about 3 grams of fat, is enough. But this advice needs to be incorporated into any prescription for a low-fat vegan diet and there are instances where it is not. So, this is not really a fault of low-fat patterns, but is more a fault of the advice sometimes given about this eating style.
Low-Fat Vegan Diets Can be Too Low in Protein
In a recent study comparing a low-fat vegan diet with a Mediterranean diet, subjects were more likely to lose weight while eating the vegan diet, but 40% of the weight lost was lean tissue.7 The truth is that it’s hard to lose weight without losing some muscle in the process. And of course, vegan diets can maintain (and build) muscle mass. In this case, though, the vegan diet seemed to be low in protein. Participants consumed a diet that was around 12% protein with an average intake of 1315 calories per day when eating the vegan diet. This works out to 39.5 grams of protein. Other studies suggest similarly low protein intakes with very low-fat vegan patterns.1,2,6
For the older subjects in the study, this amount of protein is much too low under any circumstances. And it’s also too low for anyone who is experiencing weight loss. Adequate protein consumption along with exercise is important for protecting muscle and bones when calories are restricted.17 All of these considerations are especially important for vegans since those who eat a diet based on whole plant foods probably have higher protein requirements.
Lower protein intake may help explain why, in the vegan vs Mediterranean diet study, the vegan diet was associated with smaller benefits in blood pressure reduction despite greater weight loss. Protein, especially from plants, may be beneficial for lowering blood pressure.18-20 Diets higher in monounsaturated fats – like the ones found in olive oil – are also effective in lowering blood pressure.20,21 A diet that is low in both protein and fat may not be the best choice for treating hypertension, even if it leads to weight loss.
Increasing protein intake on a vegan diet isn’t difficult. It’s a matter of emphasizing legumes over grains, choosing some gently processed foods like tofu, and maybe even more processed foods like veggie meats or protein powders. Yes, a focus on whole plant foods is valuable, but not if it morphs into a fear of all processed foods, including those that might help someone meet protein needs while eating a low-calorie diet.
Low-Fat Diets Are Not Unique for Weight Loss
A meta-analysis of 48 studies found that significant weight loss was achieved with any low-carbohydrate or low-fat diet.22 That is, restrictive diets work no matter what kinds of foods are being restricted. The problem is that many people are less likely to stick with more restrictive versions of diets whether they are low-fat or low-carb.23 Lifelong healthy eating has to involve an eating pattern you enjoy and for many people that’s one that includes higher-fat foods.
Low-Fat Vegan Diets Send a Problematic Message About What It Means to Eat Healthfully as a Vegan
These diets are sometimes touted as a way to lose weight or improve heart health without having to count calories. But, while there are no limits on portion sizes, certain foods are off-limits with this approach. It’s every bit as restrictive as calorie counting, keto dieting, or any of the many approaches to dieting that are built around stringent food rules. Eating patterns involving elimination of whole categories of foods for weight loss have more in common with fad diet approaches than with a lifestyle approach that focuses on health and enjoyment. For some, it can promote unhealthy perspectives about food. It can also deter people from even considering a vegan diet if they believe that the way to eat healthfully as a vegan is to avoid higher-fat foods. In any case, it’s not an evidence-based principle since there are no foods you have to give up entirely in order to be healthy.
What’s the Best Vegan Diet?
The best vegan diet is one that is rich in fiber, low in saturated fat, provides adequate nutrition, and fits your personal needs, including food preferences, resources, and food availability. Some vegans prefer a low-fat diet and that’s okay. I am not saying that low-fat eating is universally bad. If you ensure adequate intakes of ALA and give extra attention to choosing protein-rich foods, it’s fine to eat a diet that limits higher-fat foods — as long as this is the way you enjoy eating.
But in terms of the way we talk about healthy eating for vegans, there is no reason to believe that a diet that shuns all high-fat plant foods is somehow superior to vegan diets that include nuts, seeds, avocados and vegetables oils. Low-fat diets have no particular benefits for either health or weight loss.
1.Barnard ND, Scialli AR, Bertron P, Hurlock D, Edmonds K, Talev L. Effectiveness of a low-fat vegetarian diet in altering serum lipids in healthy premenopausal women. Am J Cardiol. 2000; Apr 15;85(8):969-72.
2. Barnard ND, Scialli AR, Turner-McGrievy G, Lanou AJ, Glass J. The effects of a low-fat, plant-based dietary intervention on body weight, metabolism, and insulin sensitivity. Am J Med. 2005; Sep;118(9):991-7.
3. Barnard ND, Cohen J, Jenkins DJ, et al. A low-fat vegan diet and a conventional diabetes diet in the treatment of type 2 diabetes: a randomized, controlled, 74-wk clinical trial. Am J Clin Nutr. 2009;89(5):1588S–1596S.
4. Ferdowsian HR, Barnard ND, Hoover VJ, Katcher HI, Levin SM, Green AA, Cohen JL. A multicomponent intervention reduces body weight and cardiovascular risk at a GEICO corporate site. Am J Health Promot. 2010; Jul-Aug;24(6):384-7.
5. Mishra S, Xu J, Agarwal U, Gonzales J, Levin S, Barnard ND. A multicenter randomized controlled trial of a plant-based nutrition program to reduce body weight and cardiovascular risk in the corporate setting: the GEICO study. Eur J Clin Nutr. 2013; Jul;67(7):718-24.
6. Kahleova H, Tura A, Hill M, Holubkov R, Barnard ND. A plant-based dietary intervention improves beta-cell function and insulin resistance in overweight adults: A 16-week randomized clinical trial. Nutrients. 2018;10(2):189.
7. Barnard ND, Alwarith J, Rembert E, et al. A Mediterranean Diet and Low-Fat Vegan Diet to Improve Body Weight and Cardiometabolic Risk Factors: A Randomized, Cross-over Trial. J Am Coll Nutr. 2021;1-13.
8. Rolls BJ. The relationship between dietary energy density and energy intake. Physiol Beha. 2009;97(5):609-615.
9. Raynor HA. Can limiting dietary variety assist with reducing energy intake and weight loss?. Physiol Behav. 2012;106(3):356-361.
10. Jenkins DJ, Wong JM, Kendall CW, Esfahani A, Ng VW, Leong TC, Faulkner DA, Vidgen E, Paul G, Mukherjea R, Krul ES, Singer W. Effect of a 6-month vegan low-carbohydrate (‘Eco-Atkins’) diet on cardiovascular risk factors and body weight in hyperlipidaemic adults: a randomised controlled trial. BMJ Open. 2014; Feb 5;4(2):e003505.
11. Del Gobbo LC, Falk MC, Feldman R, Lewis K, Mozaffarian D. Effects of tree nuts on blood lipids, apolipoproteins, and blood pressure: systematic review, meta-analysis, and dose-response of 61 controlled intervention trials. Am J Clin Nutr. 2015;102(6):1347-1356.
12. Ros E. Nuts and novel biomarkers of cardiovascular disease. Am J Clin Nutr. 2009;89(5):1649S-56S.
13: Abshirini M, Omidian M, Kord-Varkaneh H. Effect of soy protein containing isoflavones on endothelial and vascular function in postmenopausal women: a systematic review and meta-analysis of randomized controlled trials. Menopause. 2020;27(12):1425-1433.
14. Blanco Mejia S, Messina M, Li SS, et al. A meta-analysis of 46 studies identified by the FDA demonstrates that soy protein decreases circulating LDL and total cholesterol concentrations in adults. J Nutr. 2019;149(6):968-981.
15. Qian F, Korat AA, Malik V, Hu FB. Metabolic effects of monounsaturated fatty acid–enriched diets compared with carbohydrate or polyunsaturated fatty acid–enriched diets in patients with type 2 diabetes: a systematic review and meta-analysis of randomized controlled trials. Diabetes Care. 2016;39:1448–1457.
16. Garg A. High-monounsaturated-fat diets for patients with diabetes mellitus: a meta-analysis. Am J Clin Nutr. 1998;67(3 suppl):577S–582S.
17. Cava E, Yeat NC, Mittendorfer B. Preserving Healthy Muscle during Weight Loss. Adv Nutr. 2017 May 15;8(3):511-519.
18. Chan Q, Stamler J, Griep LM, Daviglus ML, Horn LV, Elliott P. An Update on Nutrients and Blood Pressure. J Atheroscler Thromb. 2016;23(3):276-289.
19. Altorf-van der Kuil W, Engberink MF, Brink EJ, van Baak MA, Bakker SJ, Navis G, van’t Veer P, Geleijnse JM: Dietary protein and blood pressure: A systematic review. PloS One 2010;5:e12102
20. Appel LJ, Sacks FM, Carey VJ, et al. Effects of protein, monounsaturated fat, and carbohydrate intake on blood pressure and serum lipids: results of the OmniHeart randomized trial. JAMA. 2005;294(19):2455–2464.
21. Schwingshackl L, Strasser B, Hoffmann G: Effects of monounsaturated fatty acids on cardiovascular risk factors: A systematic review and meta-analysis. Ann Nutr Metab 2011;59:176–186
22. Johnston BC, Kanters S, Bandayrel K, Wu P, Naji F, Siemieniuk RA, Ball GD, Busse JW, Thorlund K, Guyatt G, Jansen JP, Mills EJ. Comparison of weight loss among named diet programs in overweight and obese adults: a meta-analysis. JAMA. 2014; Sep 3;312(9):923-33.
23. Dansinger ML, Gleason JA, Griffith JL, Selker HP, Schaefer EJ. Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial. JAMA. 2005; Jan 5;293(1):43-53.