Scientific Update
A Review of Recent Scientific Papers Related to Vegetarianism
By Reed Mangels, PhD, RD
Plant Sources of Protein Associated with a Lower Risk of Physical Decline in Older Women
Frailty is the loss of strength and energy that can occur with aging. This condition can negatively affect quality of life and increases the risk of falls, illnesses, hospitalizations, nursing home admissions, and death. Two recent reports examined the relationship between dietary protein sources and the risk of frailty in older women. Both reports were based on data from the Nurses' Health Study, a long-term study of more than 85,000 women.
Researchers regularly asked study subjects who were aged 60 and older at the start of the study about their diet and health. The study subjects were followed for up to 22 years. Frailty was assessed by asking the women about their energy level, strength (ability to walk up a flight of stairs), aerobic capacity (ability to walk several blocks), recent unintentional weight loss, and presence of several chronic diseases.
During the study period about 15% of the women developed frailty. One report1 focused on meat consumption and found that women who had higher intakes of red or processed meat had an increased risk of developing frailty. The researchers estimated that replacing one serving a day of processed meat with a serving of nuts would reduce the risk of frailty 26%; replacement with legumes would reduce risk 13%. Replacing a serving a day of red meat with nuts would reduce risk 14%.
The second report2 focused on sources of dietary protein and determined that women with a higher intake of plant protein had a lower risk of developing frailty than those with a lower intake of plant protein. Sources of plant protein included dried beans, nuts, pasta, breads, and cereals. Replacing 5% of calories from animal protein with plant protein was estimated to reduce the risk of developing frailty by 38%. If plant protein replaced 5% of dairy protein, frailty risk was reduced 32%, and if plant protein replaced 5% of non-dairy animal protein (meat, fish, eggs), frailty risk was reduced 42%. Although study subjects were not vegans, the results suggest that a vegan diet featuring generous amounts of plant sources of protein could reduce the risk of developing frailty in older women.
1 Struijk EA, Fung TT, Sotos-Prieto M, et al. Red meat consumption and risk of frailty in older women. J Cachexia Sarcopenia Muscle. 2022;13:210-219.
2 Struijk EA, Fung TT, Rodríguez-Artalejo F, et al. Protein intake and risk of frailty among older women in the Nurses' Health Study. J Cachexia Sarcopenia Muscle. 2022;13:1752-1761.
Ultra-Processed Foods and Mortality
Ultra-processed food products are foods that are ready to heat or to eat and that require little or no preparation. They are typically high-calorie, high-sodium, low-fiber foods that contain little protein and few vitamins or minerals.
Examples of ultra-processed foods include ready-to-eat snacks and desserts, soft drinks, margarine, frozen pizza and other frozen entrées, processed meats, and instant soups.
A recent study investigated the association between use of ultra-processed foods and mortality in more than 77,000 participants in the Adventist Health Study-2, a study of Seventh-day Adventist adults in the United States and Canada. The Adventists are a relatively long-lived, health-conscious group. About 28% are characterized as lacto-ovo vegetarians and 8% as vegans. The study subjects were asked about the foods that they ate at the start of the study and then were followed for an average of 7.5 years. The researchers categorized foods that the subjects reported eating as unprocessed (grains, legumes, nuts, fruits, vegetables, fresh meat, and dairy milk), moderately processed (e.g. canned beans and vegetables, unsweetened canned fruits, and salted nuts), and ultra-processed. Commercial vegetarian products, such as meat analogs and breakfast cereals, were categorized as either "moderately-processed" or "ultra-processed" depending on their number of ingredients and added sugar content.
Subjects with higher intakes of ultra-processed foods tended to have a much lower consumption of fiber, fruits, legumes, nuts, and seeds and a much higher consumption of saturated fat, dairy products, red meat, eggs, and sweetened beverages than other study subjects. They were much less likely to be vegan. Those eating the most ultra-processed foods (averaging 48% of calories from ultra-processed foods) had a 14% greater risk of mortality compared to those eating the lowest amount of ultra-processed foods. The association of an increased risk of death that comes with a higher consumption of ultra-processed foods remained even after statistical techniques were used to account for differences in animal product intake. In other words, even vegetarians and vegans who ate lots of ultra-processed foods had a higher risk of mortality than those who ate lower amounts of ultra-processed food.
Orlich MJ, Sabaté J, Mashchak A, et al. Ultra-processed food intake and animal-based food intake and mortality in the Adventist Health Study-2. Am J Clin Nutr. 2022;115:1589-1601.
Large Study from the United Kingdom Examines the Risk of Some Common Cancers in Vegetarians
The UK Biobank study includes 500,000 people living in the United Kingdom who were between 40 and 69 years old when the study began. Study subjects regularly provide blood samples as well as detailed information about their diet and other lifestyle issues. This information is linked to their health care records. A recent report from this ongoing study examined cancer risk among more than 400,000 subjects with no prior history of cancer who were classified based on their dietary information as meateaters (meat or poultry more than 5 times a week), low meateaters, fish-eaters, and vegetarians. About 1.8% of the subjects were vegetarians, and about 5% of the vegetarian group were vegans. Because of the small number of vegans, they were included in the vegetarian group for analysis. The subjects were followed for an average of 11.4 years to see who developed cancer. Compared with meateaters, vegetarians had a 14% lower risk of cancer overall. Vegetarian postmenopausal women had an 18% lower risk of developing breast cancer, which was mainly attributed to their lower average Body Mass Index (BMI). Vegetarian men had a 31% lower risk of developing prostate cancer and a 43% lower risk of developing colorectal cancer compared to male meateaters.
Watling CZ, Schmidt JA, Dunneram Y, et al. Risk of cancer in regular and low meat-eaters, fish-eaters, and vegetarians: a prospective analysis of UK Biobank participants. BMC Med. 2022;20:73.
Vegans Have a Lower Risk of Digestive System Cancer
Cancers that affect the digestive system include cancer of the esophagus, the stomach, the liver, the pancreas, and the large intestine (also called colorectal cancer). Since food passes through the digestive system regularly, dietary composition, or the make-up of one's diet, could have an effect on one's risk of digestive system cancers. Chinese researchers conducted a meta-analysis (a technique in which results from a number of studies are combined) examining the relationship between plant-based diets and digestive system cancers. Their definition of "plant-based" was broad and included studies of semi-vegetarians, low meateaters, those eating a Mediterranean-style diet, lacto-ovo vegetarians, and vegans. The studies used in the meta-analysis included 14 studies that reported on cancer incidence in people on vegan diets. When these studies of vegans were examined, overall, vegans had a markedly lower risk of cancers of the digestive system compared to those not eating "plant-based" diets. The risk of digestive system cancers was not significantly different in vegans compared to non-vegans eating what the study described as "plant-based" diets.
Zhao Y, Zhan J, Wang Y, Wang D. The relationship between plant-based diet and risk of digestive system cancers: A meta-analysis based on 3,059,009 subjects. Front Public Health. 2022;10:892153.
