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People who follow a low-carb diet consume more calories on average than those who follow a low-fat diet, according to a new study, although both diets can result in similar levels of total weight loss.
“There [are] benefits for both of these diets,” says Kevin Hall at the National Institute of Diabetes and Digestive and Kidney Diseases in Maryland. “It’s a lot more complicated than a lot of the diet gurus and folks would have you believe.”
Hall and his colleagues studied 20 volunteers who were admitted to a clinic for the duration of the study. Ten were put on a plant-based, low-fat diet for two weeks and the other 10 were placed on an animal-based, ketogenic, low-carb diet. After two weeks on one diet, the participants were swapped to the other diet for a further two weeks.
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Participants were free to eat as much as they wanted from whichever diet they were on, and Hall and his team monitored their calorie intake as well as their weight, body fat and insulin levels after meals.
On both diets, volunteers lost between 1 and 2 kilograms, on average, but people on the low-fat diet consumed fewer calories and lost body fat at a higher rate than people who followed the low-carb diet. However, those on the low-carb diet experienced less variability in blood sugar and insulin levels after meals.
“It’s a mixed bag,” says Hall. “If you think that large swings in glucose and insulin are potentially harmful, then the ketogenic diet came out the winner,” he says. “But there are benefits to the low-fat diet – they lost a greater percentage of their weight coming from body fat.”
“Maybe studies like this can help us distinguish between what diets are better targeted to different people,” says Hall. “If you think your insulin surges are particularly harmful, then the ketogenic diet might be for you. If you’re worried about triglyceride [a constituent of fat] levels in your blood going up too high after meals, then clearly the low-fat diet was better.”
David Unwin, a family doctor at Norwood surgery in Southport, UK, points out that two weeks may not be enough time for volunteers to adapt to a ketogenic diet. It will be important to investigate the longer-term effects of both diets, he says.
Whatever dietary option someone chooses, regular feedback from healthcare providers can be important. “In clinical practice, I find it works so well to support people in their dietary choices whilst supplying feedback as to how their metabolic health is progressing,” says Unwin.
Journal reference: Nature Medicine, DOI: 10.1038/s41591-020-01209-1
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