SCIENTIFIC UPDATE
By Reed Mangels, PhD, RD
Vegetarian Diet Reduces Risk of Cardiovascular Disease
The term cardiovascular disease refers to conditions that affect the heart or blood vessels. These conditions can lead to events like heart attacks, strokes, and heart failure. According to the U.S. Centers for Disease Control and Prevention (CDC), one person in the United States dies from cardiovascular disease every 33 seconds. We know that vegetarians and vegans have a lower risk of having or dying from cardiovascular disease. A recent study of people with cardiovascular disease or at a high risk for developing cardiovascular disease found that their condition improved when they followed a vegetarian diet for at least six months.
This study was a meta-analysis, which means that the results from a number of other studies were combined using statistical techniques. The authors of this meta-analysis combined the results of 20 studies in which some people were randomly assigned to follow a vegetarian diet and some were randomly assigned to follow a nonvegetarian diet. The most common type of vegetarian diet that was prescribed was a vegan diet, but the meta-analysis also included studies using lacto-ovo and lacto vegetarian diets.
Overall, those assigned to a vegetarian diet (vegan/lacto-ovo vegetarian/lacto vegetarian) had modest but clinically significant decreases in risk factors for cardiovascular disease, including LDL-cholesterol, weight, and hemoglobin A1C. Hemoglobin A1C is an indicator of blood sugar levels. In eight of the studies, the dose of medications for high blood sugar, high blood cholesterol, and/or high blood pressure could be reduced in subjects following vegetarian diets. This study suggests that vegetarian diets could be useful for reducing the risk of cardiovascular disease.
Wang T, Kroeger CM, Cassidy S, et al. Vegetarian dietary patterns and cardiometabolic risk in people with or at high risk of cardiovascular disease: A systematic review and meta-analysis. JAMA Netw Open. 2023;6:e2325658.
Iron-Fortified Vegetables
The form of iron that is found in plant foods is better absorbed when eaten with a source of vitamin C. That's why some researchers propose increasing the amount of iron in vegetables that are naturally high in vitamin C, such as bell peppers and broccoli. The iron content of vegetables could be increased by breeding vegetables so that they better absorb iron from the soil and transfer it to the parts of the plant that are eaten. Another method could be to selectively breed plant varieties that are rich in iron and vitamin C and low in substances that interfere with iron absorption. German researchers wondered if consumers would accept vegetables that had been bred to have a higher iron content. They surveyed 1,000 adults and asked them if they would prefer iron-biofortified vegetables, an iron-fortified fruit drink, or a dietary supplement containing iron. The majority of respondents rated iron-biofortified vegetables higher for being healthy, sustainable, safe, and suitable for everyday use, and 77% indicated that they would prefer iron-biofortified vegetables to improve their iron supply. These iron-biofortified vegetables could be a way to increase dietary iron intake on a plant-based diet.
Welk AK, Mehlhose C, Daum D, Enneking U. Vegetables with enhanced iron bioavailability-German consumers' perceptions of a new approach to improve dietary iron supply. Nutrients. 2023;15:2291.
Muscles Without Meat
There is good evidence that a combination of resistance exercise and a relatively high protein intake increases muscle mass and strength. Most studies in this area have used animal-derived protein supplements to increase protein intake. A recent study compared the effect of high-protein vegan and omnivorous diets during resistance exercise training on muscle development. In the first part of the study, 16 healthy young adults were placed on either a vegan or a nonvegetarian diet for three days. All diets were high in protein and provided 1.8 grams of protein per kilogram of body weight (0.8 grams of protein per pound of body weight). The main protein source for vegans was mycoprotein (protein from mushrooms), which provided over a third of the vegan group's protein. Participants did resistance exercise on one leg only on the three days of this part of the study. As would be expected, the rate of muscle growth was higher in the exercised leg compared to the rested leg. Participants on vegan and nonvegetarian diets had similar rates of muscle growth in their exercised leg.
In the second part of the study, 22 healthy young adults were placed on either a vegan or a nonvegetarian diet, similar to the diet in the first part of the study. The second part of the study lasted for 10 weeks and during this part, all participants completed a high-volume resistance exercise program. At the end of the study, muscle growth, lean body mass, and strength were measured. After the resistance training, subjects on the vegan diet had an increase in their muscle size, lean body mass, and strength that was similar to what was seen in the subjects on a nonvegetarian diet.
The results of this study suggest that a combination of a higher protein vegan diet and resistance exercise training can effectively increase muscle growth and strength.
Monteyne AJ, Coelho MOC, Murton AJ, et al. Vegan and omnivorous high protein diets support comparable daily myofibrillar protein synthesis rates and skeletal muscle hypertrophy in young adults. J Nutr. 2023;153:1680-1695.
Longer Family Meals = More Vegetables and Fruits Eaten
Many children fall short when it comes to eating vegetables and fruits. Researchers in Germany wondered what would happen if children's meals lasted a little longer. Would they eat more of everything or only of certain foods? They studied 50 parent-child pairs in a family meal laboratory. The children were 6-11 years old. Study participants were observed eating two evening meals. The meals were typical German evening meals of sliced bread, slices of cheese and meat, and bite-sized pieces of fruits and vegetables. The foods served reflected each child's food preferences. In the control meal, each pair ate the evening meal in the same amount of time they usually spent on their dinner meal. In the second part of the study, each pair had 50% more time (or about 10 minutes more) to eat their meal.
The children ate 7-10 more pieces of vegetables and fruit at the longer meal. This increase was the equivalent of about one portion of fruits and vegetables combined. They did not eat more bread, cheese, or meat in the longer meal compared to the control meal. This simple strategy, of staying at the table for a little more time, could be a way to improve children's diets.
Dallacker M, Knobl V, Hertwig R, Mata J. Effect of longer family meals on children's fruit and vegetable intake: A randomized clinical trial. JAMA Netw Open. 2023;6:e236331.
Distance Racing While Vegan
Researchers from Austria, Germany, and Switzerland surveyed 245 physically fit long-distance runners who were mostly from Germany and Austria. The runners were not professional athletes. About 45% were nonvegetarians, almost 40% were vegans, and the remainder were nonvegan vegetarians. Almost half of the men followed a vegetarian or vegan diet. A greater proportion of women followed a vegan diet, compared to men.
The runners reported their best times for distance events. No significant difference was found between diet groups for their best time for a half marathon or a marathon. This suggests that vegan diets are well-suited for distance running performance. The authors of this study suggest than vegan women may have a performance advantage in distance events; additional research is needed to investigate this possibility.
Wirnitzer K, Tanous D, Motevalli M, et al. Racing experiences of recreational distance runners following omnivorous, vegetarian, and vegan diets (Part B)-Results from the NURMI Study (Step 2). Nutrients. 2023;15:2243.
