Eat carbs, lose weight – lessons from a vegan diet

This month the results of a small study of diet and weight loss from the University of South Carolina  failed to generate big headlines, yet after comparing the weight loss achieved by five groups of people on five different diets it found that those who lost the most weight were the ones on a vegan diet – meaning no animal foods at all – but quite a lot of carbohydrates.

After six months, the vegan group had lost more than twice the weight of the non-vegetarians, an average of 7.4 kilograms compared with just over three kilograms in the meat eaters,  the semi-vegetarians (who occasionally ate meat) and the pesco-vegetarians (who ate fish). The vegetarians (who also ate eggs and dairy) came a close second, averaging 6.3 kilograms.  

It's not the first study to show weight loss success on a diet based entirely on plants. Six years ago I interviewed  Dr Neal Barnard, Adjunct Associate Professor of Medicine at George Washington School of Medicine, about his research looking at using a plant food-only diet to control type 2 diabetes. He found that besides controlling blood glucose more effectively than the standard American Diabetes Association diet, the diet also helped reduce weight and cholesterol.

That's not to say that everyone who needs to lose weight should scratch meat and dairy from their shopping list but at a time when low carb is often sold as the only true path to weight loss, it's a reminder that there is more than one way to shift excess weight, says Dr Kate Marsh, an Accredited Practising Dietitian and author of The Low GI Vegetarian Cookbook.

"One advantage of a vegan diet for weight loss is that it can be very filling – this is partly because it's very high in fibre but also because foods like legumes and whole grains have a lower GI (Glycaemic Index) so they help you feel full.  Diets that are high in fibre and low GI have been shown to help with weight loss," she says. "With a vegan diet you can also eat a large volume of food without necessarily consuming a lot of kilojoules. And one of the hardest things about sticking to a weight loss plan is being hungry."

The focus on low-carb diets for weight loss also ignores the evidence that quality carbohydrates such as legumes and whole grains – staple foods on a vegan diet – can be a weight loss ally, not the enemy, Dr Marsh says.

"It's true that if you follow a low carbohydrate diet you are likely to lose weight as you cut out a lot of processed carbohydrates that can contribute to weight gain and disease risk. But not all carbs are the same and it's the quality of the carbohydrates that counts. I don't think there's any research that suggests that cutting out whole grains and legumes will make you healthier – in fact the opposite is true."

What about the argument that eating a lot of carbohydrates forces the body to produce too much insulin, which in turn encourages the body to store fat more easily?

"If this was the case, we wouldn't have studies consistently showing that vegetarians, who typically eat more carbohydrate, have better insulin sensitivity, a reduced risk of diabetes and heart disease and are less likely to be overweight," she says. 

But another advantage of a vegan diet may have something to do with the kind of bacteria that reside in a gut where the only available food comes from plants. New research from the City University of New York has found that the gut microbe population of people on a vegan diet is different to that of omnivores and includes more of the microbes thought to help protect against obesity and diabetes. 

"It's very early research but it might be another mechanism by which a vegan diet may help with weight management," Dr Marsh says.  

SMH