Scientific Update
A Review of Recent Scientific Papers Related to Vegetarianism
By Reed Mangels, PhD, RD
Early Menopause
Typically, natural menopause occurs between age 45 and 55. Early menopause, defined as the cessation of menstrual periods before age 45, is associated with an increased risk of osteoporosis, diabetes, and cardiovascular disease. Early menopause may be partially due to genetics, but diet may also play a role.
A recent study involved more than 116,000 women who were followed for more than 20 years. Participants' diets were evaluated using a "healthful plant-based diet index" and an "unhealthful plant-based diet index." The researchers identified "healthful plant foods" as whole grains, beans, fruits, vegetables, nuts, and vegetable oils. Less healthful plant foods were identified as fruit juices, sugary desserts, sugar-sweetened beverages, refined grains, and potatoes. Those eating more foods from a group (like unhealthful plant foods) received a higher score in that group. As the unhealthful plant-based diet index score increased, subjects' risk of early menopause increased.
In this study, a "plant-based diet" is not a vegetarian diet but is a diet that is higher in plant foods. Higher scores on the healthful plant-based diet index were not associated with risk of early menopause.
Grisotto G, Langton CR, Li Y, et al. Association of plant-based diet and early onset of natural menopause. Menopause. 2022;29:861-867.
Organic, Plant-Based Diets Are Good for People and the Earth
Organic farming has been shown to offer environmental benefits, including enhanced biodiversity and improved soil health; however, little is known about the human health benefits of organic food consumption. A large study from France compared the health of consumers using generous amounts of organic foods to non-consumers. High-organic-food consumers were much more likely to be vegetarians than were non-consumers and ate more nutritious diets that were more in accord with dietary guidelines. High organic food consumers were less likely to develop diabetes, metabolic syndrome, post-menopausal breast cancer, and lymphomas.
Not surprisingly, the cost of a diet based on organic food was higher than one including more conventional food. Cost figures do not take into account the cost of health impacts, air and water pollution, and biodiversity loss that are associated with the current food system. The researchers note that higher costs of organic foods contribute to health inequalities and that these higher costs should be addressed by governmental interventions. This study was part of the French BioNutriNet Project whose main conclusion is "organic-based diets should be accompanied by dietary shifts toward plant-based diets to allow for better planetary and human health."
Kesse-Guyot E, Lairon D, AllèB, et al. Key findings of the French BioNutriNet Project on organic food-based diets: Description, determinants, and relationships to health and the environment. Adv Nutr. 2022;13:208-224.
The Dietary Pattern in Dietary Guidelines for Americans Could Easily be Made Vegan and Nutritionally Adequate
Dietary Guidelines for Americans is a document the U.S. government produces every 5 years and used as the foundation for federal nutrition education materials as well as being used by schools, the food industry, and many others. The most recent Dietary Guidelines, released in 2020, endorses "a healthy vegetarian dietary pattern" as one of three recommended dietary patterns.
The "Healthy Vegetarian Dietary Pattern" includes eggs and has no suggestions for vegan foods that could replace eggs. A recent study provides evidence that it would be easy to modify the vegetarian dietary pattern in Dietary Guidelines to make it vegan. In this study, the "dairy food group" was replaced with fortified soymilk and fortified soy yogurt. Eggs were replaced with a combination of beans, peas, lentils, nuts, seeds, and soy foods. Vegan patterns were created to be similar in calories to the original "Healthy Vegetarian Dietary Pattern." The resulting vegan dietary patterns were analyzed for nutritional adequacy and compared to the original "Healthy Vegetarian Dietary Patterns," which contained dairy products and eggs.
The vegan patterns were higher in iron, copper, vitamin D, riboflavin, vitamin B12, and vitamin K. Protein was slightly lower but still adequate. Sodium, cholesterol, and zinc were lower in the vegan patterns. Other nutrients were similar in both patterns.
This study only looked at nutritional adequacy for non-pregnant, non-lactating adults. The hope is that future studies will examine other age and life-cycle groups. Additional studies should examine the use of other fortified plant milks and determine the minimum amount of these products needed and examine the need for supplements if fortified foods are not used as sources of vitamin D, calcium, and vitamin B12.
We hope that the results of these and similar studies will be used to include vegan dietary patterns in the next edition of Dietary Guidelines for Americans.
Hess JM. Modeling dairy-free vegetarian and vegan USDA food patterns for non-pregnant, non-lactating adults, J Nutr. 2022;152:2097-2108.
Tomatoes as a Vitamin D Source?
Generally, plants are poor sources of vitamin D, but a recent report suggests that tomatoes, and possibly other plants, could be genetically altered to increase their vitamin D production. Researchers used genetic engineering to increase production of vitamin D3 in tomato plants. This did not involve the use of any animal cells or genes and the modifications did not affect the growth, development, or yield of the plants. Tomatoes from these plants would need to be exposed to ultraviolet light to increase their vitamin D content. Following that exposure, one tomato would have around 10% of the Daily Value for vitamin D. The leaves of the genetically altered tomato plant could be used to manufacture a vitamin D3 supplement that could be used by vegans. These products (tomatoes and plants) are not commercially available.
Li J, Scarano A, Gonzalez NM, et al. Biofortified tomatoes provide a new route to vitamin D sufficiency. Nat Plants. 2022;8:611-616.
Dairy Products and Prostate Cancer Risk
After skin cancer, prostate cancer is the most common cancer in American men. Prostate cancer risk was recently studied in more than 28,000 men enrolled in the Adventist Health Study-2, a large long-term study of Seventh-day Adventists. The risk of prostate cancer was approximately 25% higher among men with the highest daily consumption of dairy products (about 14 ounces daily) compared to those with the lowest consumption (less than an ounce a day). The least risk was seen in those not consuming dairy products, who had approximately a 60% lower risk of developing prostate cancer compared to those with the highest dairy product consumption.
The increased risk of prostate cancer seen with higher dairy product consumption did not appear to be related to calcium. Those with higher and lower calcium intakes—whether from diet, supplements, or a combination of diet and supplements—did not differ in their risk of prostate cancer. The researchers analyzed the data both with and without vegans since there could be other protective factors in vegan diets in addition to avoidance of dairy products.
Even without vegans, those who consumed large amounts of dairy products still had a markedly higher risk of prostate cancer than did those not consuming dairy products. The increased risk of prostate cancer associated with dairy products appeared mainly to be due to greater consumption of milk; yogurt and cheese consumption did not seem to influence the risk of prostate cancer. Cow's milk consumption, whether reduced-fat or full-fat, did.
Orlich MJ, Mashchak AD, Jaceldo-Siegl K, et al. Dairy foods, calcium intakes, and risk of incident prostate cancer in Adventist Health Study-2. Am J Clin Nutr. 2022;116:314-324.
