Is a vegan diet nutritionally adequate?
The vegan diet has gained much popularity over the last decade. Promotion of the diet by celebrities and athletes has increased awareness of the many health benefits of veganism. In fact, as many as 3-6% of US consumers report being vegan. This is a significant increase, compared to just 1% in 2014.
The American Institute for Cancer Research recommends a plant-based diet, urging people to consume two-thirds of their diet from vegetables, fruits, whole grains and beans. According to the 2015-2020 Dietary Guidelines for Americans, vegetarian diets are recommended as one of three healthy eating patterns, and the guidelines provide meal plans to help guide you.
Retail sales of plant-based foods have risen 11% from 2018-2019, with a market value of $4.5 billion. Also, many restaurants and fast-food establishments have begun providing plant-based options. Common reasons people choose the vegan diet include religious and ethical views, environmental concerns, cultural and social principles, as well as the potential health benefits.
What exactly is a vegan diet?
The vegan diet is a form of vegetarianism. Vegetarians are classified based on the exclusion of specific foods. Vegans have the strictest dietary elimination, omitting any animal foods and their byproducts. Other types of vegetarians include lacto-vegetarians (excluding meat, fish and eggs but allowing dairy products), ovo-vegetarians (excluding meat, fish and dairy products but allowing eggs), and lacto-ovo-vegetarians (excluding meat and fish but allowing dairy and eggs). There are also pescetarians, who follow a diet that restricts meat consumption to only fish and seafood.
What are the benefits of a vegan diet?
The benefits of eating more fruits and vegetables while reducing fat intake from meat are undeniable. According to the Academy of Nutrition and Dietetics, those who follow a well-planned vegetarian or vegan diet can have a reduced risk of diseases such as ischemic heart disease, Type 2 diabetes, high blood pressure, obesity and certain types of cancer.
The EPIC-Oxford study, one of the largest studies of vegetarians in the world, showed that those who consumed a vegan diet ate the most fiber, the least total fat and saturated fat, and had the healthiest body weights and cholesterol levels compared to meat eaters and other vegetarians.
Nutrients and supplementation
In the Adventist Health Study-2, which included 73,308 Seventh-day Adventists, it was discovered that vegans had the lowest blood pressure levels and the least hypertension compared to vegetarians and meat eaters. However, less is known about any negative health implications from the vegan diet, such as nutrient deficiencies.
There is debate as to whether a vegan diet should be supplemented with certain nutrients since studies suggest people following this diet are more likely to have nutrient deficiencies. In addition, since almost all countries include meat and dairy in their food-based dietary guidelines, one might wonder if a vegan diet is healthy on a long-term basis.
This proposes the question, is the vegan diet nutritionally adequate as a life-long eating pattern? Let’s dive in.
A systemic review was conducted, which included 48 studies with a total of 12,096 vegan subjects. The aim of the study was to assess the adequacy of a vegan diet compared to the World Health Organization dietary recommendations. Researchers looked at total energy intake, macronutrients and micronutrients. The risk of deficiencies was assessed, as well as the effect of veganism on health and body mass index (BMI).
Not surprisingly, the vegan diet had the lowest total energy intake, followed by vegetarians. Vegan diets did meet the WHO recommendation for energy intake, with intakes ranging from 1,672 and 2,055 calories per day. The main energy sources for vegans were carbohydrates and soy proteins.
Fiber intake was higher in vegans compared to omnivores, with more than 30 grams per day. High-fiber diets have been shown to play a significant role in blood glucose control and have a protective effect against insulin resistance and Type 2 diabetes. One study reported switching to a plant-based diet reduced the incidence of Type 2 diabetes by 53%.
Fruits & vegetables
The highest consumption of fruits, vegetables and cereals was found in vegans. The WHO recommends a daily consumption of 400 grams of fruits and vegetables per day. Fruit and vegetable intake in vegan diets were 364.2 and 366.0 grams. Overall, the major food sources of vegans in these studies included fruits, vegetables, legumes, starchy foods, bread pastries, cereals, rye-flour products, soy products, brown rice, potatoes, meat substitutes, nuts, seeds, oils and olives.
Body mass index (BMI)
The correlation between diet type and body mass index (BMI) was assessed. Vegans were shown to have lower BMIs compared to all other diet groups. Also, the vegan group tended to have the lowest number of overweight and obese participants. Omnivore participants had the highest BMIs.
In a Swedish study, researchers found the rate of overweight or obesity was 40% among omnivores and 25% among vegetarians.
However, vegan diets were lower in protein compared with all other diets. The total energy intake from protein in the Swedish study mentioned above was 13-15%, just below the WHO recommended protein of 15%. In the study, 27.3% of vegan subjects were below the acceptable range for protein intake.
Vegans typically aim to meet their protein needs through seeds, nuts, legumes, meat substitutes and soy products. Plant-based proteins compared to animal proteins are associated with a lower risk of heart disease, slower cancer growth and lower mortality rates. Soy consumption has also been shown to be related to a low incidence of prostate cancer. Inadequate intakes of protein in vegans are more likely to occur with avoidance of legumes, seeds and nuts.
It was noted that protein needs among vegans are more likely to be met when total calorie needs are sufficient and the diet is varied.
Fat intake was lowest among vegans but not significantly different than other diets. Saturated fat intake was lower among vegans at 21 grams per day compared to 54 grams per day in omnivores. Intake of polyunsaturated fatty acids (PUFAs), omega-3 and omega-6 were higher in vegans in this review. Omega-3 fatty acids are strongly associated with the prevention of heart disease and can improve lipid profiles by reducing the inflammatory response and oxidative stress.
The adequacy of intake for B vitamins varied, with vegans having the highest intake of vitamin B1 and B6 but the lowest intake of vitamins B2, niacin and B12. The recommended intake of vitamin B12 is 2.4 ug/day, and the average B12 intake in vegans was reported to be 0-0.9 ug/day.
Low intake of B12 is a major concern with following a vegan diet due to the exclusion of meat, poultry and eggs. B12 deficiency can lead to anemia, neurological and other hematologic disorders. It is important that vegans be monitored regularly for vitamin B12 status. It has been recommended that vegans supplement their diet with vitamin B12 or consume fortified foods such as breakfast cereals, nutritional yeast, fortified plant milks (soy, almond, coconut and rice), seaweed and mushrooms.
It was also shown that vegans have lower intakes of vitamin D and calcium. Total vitamin D intake among vegans was lower than other diets; however, there were no major differences in serum vitamin D2 levels among the different groups.
In regard to calcium intake, approximately 76% of vegan subjects consumed less than the recommended daily intake of calcium. This is due to the exclusion of dairy products and the low bioavailability of calcium in plant-based foods.
Inadequate intake of calcium is related to high incidence of fractures. Vegans have been shown to have a 30% higher rate of bone fractures than meat eaters. Calcium intake can be increased by consuming more broccoli, sprouts, tofu, fortified plant milks, juices and mineral waters.
The study also revealed zinc intake is reduced while following a vegan diet, making the risk of zinc deficiency high. Meat, dairy and eggs are rich sources of zinc.
Some plant foods high in zinc, such as nuts, seeds and whole grains, have bioavailability issues due to the presence of phytates. Phytates, which can be found in beans, nuts, seeds and some grains, can lower the absorption of zinc in the intestines. Phytate content can be lowered through methods such as soaking, germination, fermentation, enzymatic intervention or genetic modification in grains.
Zinc plays an important role in the regulation of the immune system and many enzyme functions. Insufficient intake of zinc could be related to mental health disorders, such as depression, as well as dermatitis, diarrhea and alopecia.
Magnesium & vitamin E
Magnesium and vitamin E intake were found to be highest in vegan participants compared to other diets, and higher than the WHO recommended levels. The main sources of vitamin E are vegetable oils, peanuts, soybeans, wheat germ, sunflower and almonds. Interestingly, even though vitamin E intake was highest in vegans, it was not correlated to higher serum concentrations of vitamin E.
It was also found that iron intake among vegans was higher compared to other diets. Consumption of iron-rich foods, such as green leafy vegetables, grains, nuts and beans, is typically high on a vegan diet. However, the absorption of iron was not correspondingly high due to the low bioavailability of iron in plant-based foods.
The absorption of plant-based iron sources, or non-heme iron, is dependent on physiological needs and meal consumption. Research has shown non-heme iron absorption can vary from 1% to 23%. However, the overall incidence of iron deficiency anemia in vegans is no greater than in those following other diets. Iron supplementation may be considered in those more likely to have deficiencies, such as in premenopausal vegan females or those with greater iron needs due to higher losses.
Conclusions: Is the vegan diet healthy?
The results of this study reveal that adhering to a vegan diet can lead to a lower total daily calorie intake, a lower body weight and a reduced fat intake.
However, avoiding certain nutrient deficiencies can be challenging. A variety of foods, including fruits, vegetables, ample leafy greens, whole grains, nuts, seeds, soy, legumes and high-quality oils, is key. Special consideration should be given to total protein intake, vitamin B2, niacin, vitamin B12, calcium, vitamin D and zinc.
Overall, the duration of following a vegan diet seems to be a main factor in the development of deficiencies. The longer you stay on the diet, the greater your likelihood of developing deficiencies, and the greater the need for supplementation.
There are resources and apps that can help you track your intake of these important nutrients and help you identify where you might need to adjust your diet or supplement. You can also meet with a registered dietitian to assist with planning nutritionally adequate vegan meals.
Not sure how to eat healthy on a vegan diet? Connect with a dietitian today.
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