Scientific Update
by Reed Mangels, PhD, RD, FADA
A Review of Recent Scientific Papers Related to Vegetarianism
Whole-Food Plant-Based Diet During Treatment for Metastatic Breast Cancer
A recent pilot study examined whether the use of a whole-food plant-based (WFPB) vegan diet was feasible and beneficial during treatment for metastatic breast cancer. Breast cancer treatment has been associated with weight gain, increased blood cholesterol levels, and greater insulin resistance—factors that may result in poorer outcomes.
Thirty women who were being treated for stage 4 breast cancer were randomly assigned to either a WFPB diet or their usual diet for eight weeks. Those in the WFPB group received three prepared meals and a side dish every day. Meals included legumes, whole grains, nuts, seeds, fruits, and vegetables and did not include animal products or added fats and oils. Subjects were encouraged to add their own food as long as it followed the diet plan. Those in the usual diet group continued to eat the way they usually did. Both groups were given a daily multivitamin.
Over the eight-week study period, the WFPB diet group lost an average of nine pounds more than the usual diet group. This weight loss did not appear to be due to the women's cancer getting worse or to a loss of appetite. Total cholesterol and LDL cholesterol decreased more in the WFPB group, and this group had a greater decrease in insulin resistance. There was no significant difference in markers of cancer progression at the end of the study.
The researchers pointed out that this was a small pilot study that needs to be repeated for a longer time period and with more subjects.
Campbell TM, Campbell EK, Culakova E, et al. A whole-food, plant-based randomized controlled trial in metastatic breast cancer: weight, cardiometabolic, and hormonal outcomes. Breast Cancer Res Treat. 2024;205:257-266.
Vegan Diets for Male Bodybuilders
Can a vegan diet that doesn't include specialty foods, such as protein supplements, be planned to meet the calorie and nutrient needs of intensive training for male bodybuilders? Researchers used existing data about bodybuilders' height, weight, and physical activity to estimate calorie needs. They then used data about foods commonly eaten by vegans and increased the amounts of foods to develop theoretical vegan diets that would meet bodybuilders' calorie needs, which were estimated at approximately 4,200 calories per day. Diets that provided generous amounts of protein (1.8 grams of protein per kilogram of body weight) could be planned. The International Olympic Committee recommends that athletes who are training to maximize muscle size and strength take in at least 1.6 grams of protein per kilogram. The planned diets also included a recommended amount of leucine for those wanting to maximize muscle development. Leucine is described as the most important amino acid for stimulating muscle development. The diets met recommendations for all nutrients except for vitamin D, which was slightly below the RDA. Fortified foods or supplements may be needed to meet recommendations for vitamins B12 and D. The theoretical diets did not exceed recommendations for saturated fat. The researchers noted that this study modeled diets during the bodybuilding off-season as opposed to the dieting phase. During preparation for a bodybuilding contest, many competitive male bodybuilders use protein supplements to help to meet protein needs while keeping calorie intake low. Plant protein supplements may be helpful to bodybuilders following vegan diets during the dieting phase of contest preparation.
The results of this modeling study suggest that athletes can use vegan diets to achieve their muscle-building goals and meet nutrient needs while keeping saturated fat intake low.
Goldman DM, Warbeck CB, Karlsen MC. Completely plant-based diets that meet energy requirements for resistance training can supply enough protein and leucine to maximize hypertrophy and in male bodybuilders: A modeling study. Nutrients. 2024;16:1122.
Does the Addition of Olive Oil Improve a Whole-Food, Plant-Based Diet?
You've probably heard the debate—Is it healthier to only get fat from whole-food sources such as olives, nuts, seeds, and avocados or from vegetable oils? Mediterranean diets, which appear to be heart healthy, include generous amounts of olive oil. On the other hand, whole-food sources of fat provide other nutrients in addition to fat.
The Recipe for Heart Health (RFHH) study had 40 adult participants, all of whom were considered to be at borderline to high risk for heart disease. They were assigned to follow either a whole-food plant-based (WFPB) vegan diet high in olive oil (4 Tablespoons per day) or a WFPB vegan diet with less than a teaspoon of olive oil per day for four weeks. After a one-week break from their diets, they switched to the other diet for four weeks so that those who previously had a high intake of olive oil now had a low intake and vice versa. Participants attended weekly cooking classes and kept records of what they ate. Prior to the study, subjects were not on a vegan diet.
Total fat intake averaged 48% of calories on the high olive oil diet and 32% of calories on the low olive oil diet. Sources of fat during the low olive oil phase were mainly nuts, seeds, olives, and avocados. Both diets led to a significant reduction in total and LDL cholesterol, blood glucose, and C-reactive protein (an indicator of inflammation) compared to baseline. There were greater decreases in LDL cholesterol after the low olive oil diet.
The researchers would like to do a longer study to see if their results would be sustained. They support the use of a WFPB vegan diet with relatively low olive oil to reduce the risk of heart disease.
Krenek AM, Mathews A, Guo J, et al. Recipe for heart health: A randomized crossover trial on cardiometabolic effects of extra virgin olive oil within a whole-food plant-based vegan diet. J Am Heart Assoc. 2024;13:e035034.
Vegan Diets in the United Kingdom
More than 1,500 self-identified vegan adults in the United Kingdom were compared to omnivores, "flexitarians" (rarely ate meat), pescatarians, and vegetarians. The majority of study subjects had followed their current diet for at least five years. All participants completed a questionnaire about the food that they ate. The results were compared between groups and with U.K. dietary guidelines.
Vegans, on average, consumed almost three ounces of plant-based meat alternatives (tempeh, textured vegetable protein, falafel, veggie burgers/sausages, soy burgers/sausages, seitan) and almost a cup of plant milks daily. Their intakes of grains, vegetables, fruits, nuts, seeds, and dried beans were higher than that of any other diet group. Vegans ate almost three times more dried beans than did omnivores. Vegans were most likely to use vitamin and mineral supplements (87.5% of vegans used at least one supplement). About a quarter of vegans took an omega-3 fatty acid supplement, and 35-40% took a vitamin B12 supplement.
On average, all diet groups met recommended intake for protein, calcium, vitamin B12, and zinc. Only vegans met the saturated fat recommendations. The calcium intake of vegans was markedly higher than in earlier studies of vegans, probably due to greater use of fortified plant milks. All groups met the iron recommendations for men and older women; only vegans met the iron recommendation for premenopausal women. None of the groups met the vitamin D recommendation. Vegans had the highest intakes of fiber, vitamin C, and vitamin E. A higher proportion of vegans compared to nonvegetarians had intakes of zinc, iodine, selenium, vitamin A, and vitamin B12 that were below recommendations. These results were only based on food intake and did not include supplement use.
Lawson I, Wood C, Syam N, et al. Assessing performance of contemporary plant-based diets against the UK Dietary Guidelines: Findings from the Feeding the Future (FEED) Study. Nutrients. 2024;16:1336.
