Scientific Update
By Reed Mangels, PhD, RD, FADA
Vegetarian Diet Associated with a Lower Risk of Cataract
A
cataract is a clouding of the lens in the eye. Cataracts affect vision, and
eventually, many people need surgery to remove cataracts. Approximately 1.5 million
cataract operations are performed every year in the United States. Oxidative stress
damages the proteins in the lens and is thought to be a cause of age-related
cataracts.
Researchers in Taiwan studied more than 1,300 vegetarians and more than 3,000 nonvegetarians for more than five years to see whether there were differences in the development of cataracts. At the start of the study, subjects' average age was 53 years. The vegetarians were less likely to have diabetes, high blood pressure, and high cholesterol. Compared to the nonvegetarians, the vegetarians ate more vegetables, nuts, soy foods, and whole grains and had higher intakes of vitamins A and C. Being vegetarian was associated with a 20% lower risk of developing a cataract. This difference in risk may be due in part to the vegetarians' higher intake of antioxidants such as vitamins A and C and to the lower incidence of diabetes and other chronic conditions in vegetarians.
Chiu THT, Chang CC, Lin CL, Lin MN. A vegetarian diet is associated with a lower risk of cataract, particularly among individuals with overweight: A prospective study. J Acad Nutr Diet. 2020.
Vegan Diet Offers Health Benefits Regardless of Blood Type
People with blood type O have a somewhat lower risk of developing heart disease,
and those with blood type A have a higher risk than do those with other blood types.
Diet books and websites suggest that those with different blood types would benefit
from different diets; this idea is not supported by research. Investigators from the
Physicians Committee for Responsible Medicine (PCRM) looked at the response to a
lowfat vegan diet in subjects with different blood types. Subjects were on a lowfat
vegan diet for 12 weeks. Blood type was determined for 68 subjects. The 20 subjects
with blood type A had significantly higher average cholesterol and LDL cholesterol
at the start of the study than did subjects with other blood types. The 31 subjects
with blood type O had significantly lower average cholesterol and LDL cholesterol at
the start of the study than did subjects with other blood types. At the end of the
12-week study, there was no significant difference based on blood type in weight
loss or in reductions in total and LDL cholesterol. These results suggest that blood
type does not affect response to a vegan diet. Whether a person is type O, A, AB, or
B, a healthy vegan diet can promote favorable changes in body fat, body weight, and
blood lipids.
Barnard ND, Rembert E, Freeman A, Bradshaw M, Holubkov R, Kahleova H. Blood type is not associated with changes in cardiometabolic outcomes in response to a plant-based dietary intervention. J Acad Nutr Diet. 2020.
Soy Isoflavones Associated with Moderately Reduced Risk of Heart
Disease
Soybeans and foods made with soy contain substances called
isoflavones, which are believed to have health effects. Some studies find that the
risk of heart disease is reduced with higher isoflavone intakes while other studies
do not. These inconsistent results may be due to some studies having a small number
of subjects, incomplete assessment of diet composition, and a too-short follow-up
period. A recent report attempted to correct these issues. The study had more than
210,000 male and female subjects living in the United States, took place over more
than 20 years, and asked subjects about their food choices every four years. This
was an observational study, so subjects ate whatever they wanted and were followed
to see who developed heart disease. A higher isoflavone intake was associated with a
moderate reduction in the risk of heart disease. Additionally, those eating tofu
once or more a week had an 18% lower risk of heart disease than those eating tofu
less than once a month. Most study subjects ate 0.11 to 4.24 milligrams of
isoflavones per day. When compared to the median intake in Japan of 30 to 35
milligrams of isoflavones per day, this is a relatively low intake. Perhaps an even
greater reduction of risk of heart disease would have been seen with a higher intake
of isoflavones.
Ma L, Liu G, Ding M, et al. Isoflavone intake and the risk of coronary heart disease in US men and women: Results from 3 prospective cohort studies. Circulation. 2020;141(14):1127-1137.
Plant-Based Protein as Effective as Animal-Based Protein for Strength
Training
Those doing strength training typically want to build
muscles. Both resistance training and a protein-rich diet have been shown to build
muscle. Does it matter if the protein comes from plants? A recent study investigated
the effects of protein source on strength training.1 Subjects were 19
young men who had been vegan for at least a year and 19 young men who were
nonvegetarians. Subjects were physically active but had not done strength training
for at least a year before the study started. During the study, all subjects
participated in a 12-week, twice-weekly, supervised strength training program. Their
daily protein intake was increased to 1.6 grams of protein per kilogram body weight
using protein supplements (soy for vegans, whey for nonvegetarians) in addition to
their usual diet. While somewhat higher protein is associated with gains in muscle
during strength training, no further gains are seen beyond an intake of 1.6
g/kg.2
Both groups had a similar increase in muscle mass and strength over the 12-week study. These results suggest a vegan diet containing generous amounts of protein, along with strength training, can increase strength and muscle mass. This study didn't examine the effectiveness of lower (but adequate) amounts of plant-based protein during strength training.
1 Hevia-Larraín V, Gualano B, Longobardi I, et al. High-protein plant-based diet versus a protein-matched omnivorous diet to support resistance training adaptations: A comparison between habitual vegans and omnivores. Sports Med. 2021;10.
2 Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis, and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2018;52(6):376-384.
New Report Connects Food Choices and Climate Change
An
international collaboration, The Lancet Countdown, provides an independent
system that tracks the global health profile of the changing climate. Their report
for 2020 includes some sobering information about our food choices and their effects
on climate change and health. The food system accounts for 20-30% of global
greenhouse gas emissions, most of which are from dairy and meat production.
Emissions from livestock have increased by 16% since 2000; the vast majority of
these emissions (93%) are from ruminant animals. Excess consumption of red meat is
estimated to have contributed to 990,000 deaths worldwide in 2017 (the most recent
year for which figures are available). This is a 72% increase in the number of
deaths attributed to excessive red meat consumption since 1990.
One conclusion of this report is, "Excessive consumption of red meat brings considerable health consequences, and plant-based sources that are less emissions-intensive are important alternatives, particularly in Europe and the Americas where per-capita emissions are high."
The report also shows the effects of climate change on the food supply. Rising temperatures and increasingly frequent extreme weather events threaten global food security. There has been a 1.8-5.6% decline in yield potential for corn, rice, soy, and winter wheat over the past 38 years. It is increasingly difficult to even maintain current crop production levels.
Watts N, Amann M, Arnell N, et al. The 2020 report of The Lancet Countdown on health and climate change: responding to converging crises. Lancet. 2021;397(10269):129-170.
