Is a vegan diet healthy? Is it more or less effective than carbohydrate restriction for management of obesity, heart disease, and diabetes? As a dietitian who prides herself on thinking outside the box, I believe all types of diets can be embraced as long as they are healthy and meet an individual's specific nutrition needs. However, there are several nutrients that are often lacking in a strict vegan diet.
- Omega-3 fatty acids: Although walnuts, flaxseed, and chia seed are good sources of the essentail fatty acid alpha-linolenic acid (ALA), they must be converted to ecospentanoic acid (EPA) and docosohexanoic acid (DHA) found in fish and other animals. The amount of ALA needed to achieve the recommended levels of EPA and DHA is very high, the conversion is unpredictable, and the ability to convert decreases with age.
- Vitamin B-12: This nutrient is essential for brain and nerve function, among many other important things, and is found only in animal products. Vegans must take oral supplements or injections to prevent deficiency.
- Vitamin D: Another vitamin/hormone that does not occur in plants (although orange juice and many other foods are often fortified with it), we are only now beginning to understand how crucial to good health maintaining optimal vitamin D levels is.
- Protein: It is very difficult to get adequate protein on a vegan diet, and it's virtually impossible to do so without consuming a lot of carbohydrates. A vegan diet is by definition high in carbs because grains and other starchy plants must be consumed in various combination to supply complete protein.
There are studies suggesting that both vegan and low-carbohydrate diets can improve markers for cardiac risk. Although many regard a vegan diet as healthier because it contains less saturated fat, one of my previous posts on high-fat, low-carb diets argues that this way of eating can also promote cardiac health.
Replacing meat, fish, dairy, and eggs with large amounts of plant proteins like rice, corn, wheat, beans and other legumes results in a large carbohydrate load, which increases insulin requirements to maintain appropriate blood glucose levels. Given that many overweight and obese people have insulin resistance, impaired glucose tolerance, or diabetes, a vegan diet would likely worsen their glycemic control and further impair insulin sensitivity. People with Type 1 diabetes would need more insulin to cover the high amount of carbohydrates, and because smaller dosages of insulin are more predictable than larger ones, their blood sugar levels would tend to be more erratic.
Which is better to achieve and maintain weight loss, a vegan or low-carbohydrate diet? I've met and heard about many people who have had success with either plan. I hate to generalize, but most vegans I know are quite thin. Are they healthy? I'm not sure. It's hard for me to believe veganism can lead to optimal health given its nutritional limitations and the fact that we evolved on an omnivorous diet that was quite high in meat and fish. That being said, I believe everyone has a right to choose whatever diet they wish, and there are certainly healthier ways of practicing veganism, i.e., including lots of nuts, avocados, and other fats; consuming large amounts of vegetables, and supplementing aggressively with key nutrients, including amino acids. For my part, I will continue to promote a low carbohydrate lifestyle for reducing weight, improving blood sugar levels and cardiac health, and providing other important health benefits. Among my dietitian friends and colleagues, only a handful support my efforts, and one just happens to be a strict vegetarian/near vegan. Vive la Différence!