The health pros and cons of a vegan diet

Sorting the wheat from the chaff...
15 October 2024

Interview with 

Tom Sanders, King’s College London

BREAD AND CEREAL GRAINS

Sliced bread on table, next to wheat grain

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What exactly does the science say about vegan diets, and what are the main points of nutritional concern? Tom Sanders is emeritus professor of nutrition and dietetics at King’s College London. Tom has been researching vegan diets since the 1970s…

Tom - The nutrient that is most likely to be lacking in a vegan diet is going to be a vitamin B12. It may be quite low in calcium depending on the food selected and the protein quality will be a bit lower, but it won't be so low to be a problem. The diet itself, because it's derived from plant foods, means that some of the minerals, things like iron, all calcium and zinc, can be the absorption of them from plant foods can be not very good, and be influenced by other components in the diet. So sometimes that can be a problem. But really there are only a few things that are really missing in vegan diets.

Chris - What should a person do to make sure that they don't miss out on those things? Because there's a lot of focus on what people might be missing, but there's not so much focus on what they're including. So what's the best way to approach this?

Tom - I've always said if you’re looking at a diet, you want to have a good staple food. So in the West, our staple food is based on wheat. So we eat bread and all things made from flour and bread. And that's a good start. And then if you can mix the cereal with a legume or a pulse we call it, so beans, lentils, things like that, it gives you a very high quality protein, mixing the two together. And the other thing, which I think you need to make sure you have is plenty of fruit and vegetables, you need to be quite careful though with young children not to feed them too many fruit and vegetables because they've got small stomachs and then they can't eat the other foods, for example the cereals and the beans that provide most of the nutrients.

Chris - I was going to ask you about that because there must be times in our life when our needs change for various reasons. You've mentioned one of them I was going to bring up, which is little kids because they must have a bigger demand for calories to grow, for example. But another time is when you're growing a little kid, you're a pregnant woman. And if you are for instance, an elderly person who's broken something needs to get better from a surgery in hospital for example, you're going to need different energy and different dietary constituents at those points. Are there any things that people should bear in mind at those points in their lives for example?

Tom - Nutrient requirements are greatest in the first few years of life when growth is most rapid. And in slightly older children, around the adolescents going through puberty, there is also a big increase in energy and food requirements. But in older children, they're able to go and select food for themselves and eat more food. Women actually don't need to eat more food during pregnancy because the body makes a number of adaptations to cope with improved absorption of some nutrients. But it's very important when women go into pregnancy, they go into pregnancy with a good diet.

Chris - What about breastfeeding?

Tom - Breastfeeding, I think the important message I think is, it's very important that mothers who are vegan ensure they've got a good source of vitamin B12 because if the mother doesn't eat enough vitamin B12, the level of vitamin B12 will be low in the mother's milk. And that can cause vitamin B12 deficiency in the baby.

Chris - Researchers including yourself, have looked over the years at the relationships between different diets and disease outcomes. So when one does those sorts of studies, are people better off eating plant-based diets and, and in some cases extreme plant-based diets like vegans, do they have lower rates of certain diseases and higher rates of others? How does it break down?

Tom - When I first looked at it, we were trying to establish were there any problems with vegans compared with mixed diets, omnivores we call them. And our overall conclusion early on was the health of vegans differs little from that of omnivores. And I still probably stick with this. Many people who follow vegan diets also have other healthy aspects of lifestyle. They tend to be non-smokers, don't drink much alcohol, and take a lot of physical activity. And those are all good things for health. So if you adjust for those things in the analysis, there's not a huge difference. There's probably a lower risk of heart disease. And we can attribute that, I think, to the very low intake of saturated fatty acids and a slightly higher intake of polyunsaturated fats. They have low blood cholesterol levels. When it comes to cancer, we don't really have a huge amount of evidence on cancer and vegans because the largest number of, I think, we've got pulled together is only about 8,000-10,000 people followed for 15, 20 years. If we look at vegetarians compared with meat eaters, there's not any difference in risk of colorectal cancer, which is the one you might think that might be protected on. And I suspect that's the case for vegans. There's some suggestion that vegans might be at lower risk of prostate cancer, which affects elderly men. There's some suggestion that some blood cancers might be lower in vegetarians and vegans and some of these are, we know, due to infections. But it may be something more to do with lifestyle than to do with diet. But overall, I don't think there's really a huge difference in cancer compared with the effects of things like tobacco or alcohol.

Chris - And lastly then. In your view, vegan diet - good thing, bad thing?

Tom - I think it's what people want to do and I understand there are a variety of reasons why people follow vegan diets. Some of them do it because they believe they are concerned about climate change. And there are other groups like the Janes for example, in the Indian sect who follow for religious reasons. And you can follow a vegan diet, but you've got to be very careful. It's okay if you supplement it with vitamin B12, I think you need to watch out about calcium intake. But you can do that by selecting the diet properly.

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