On the ketogenic diet, the amount of calories they burned only dropped by 95 a day, compared to 423 calories a day on the low-fat diet (a reason, I think, why keto can be a more effective way to lose weight and keep it off).Īnother possible reason why our basal metabolic rates have fallen is because we now heat our houses more. Although they experienced a drop in metabolic rates whichever diet they followed (as you’d expect, because they lost weight and people carrying less weight have a slower metabolic rate), this was significantly greater when they were on the low-fat diet. In a 2012 study in the New England Journal of Medicine, 21 adults who were overweight or obese were allocated to follow a ketogenic diet for a month, followed by a low-fat diet, or vice versa. Similarly, there is evidence in humans that switching to a ketogenic diet, which is higher in fat and low in carbs, leads to a smaller fall in your metabolic rate than switching to a low-fat diet. Studies in rats have shown that when you reduce levels of saturated fat in their diets, their metabolic rates slow down. For years we were urged to reduce consumption of saturated fats because this was supposed to cut our risk of heart disease, though the evidence for this has never been that strong.Īs the researchers point out, one unintended side-effect of following this advice may have been a fall in average metabolic rates. They believe one reason for this is the major change in what we eat, with a drop in consumption of meat and dairy (which are rich in saturated fats) and a rise in ultra-processed foods high in sugary carbs. the calories we spend just staying alive) had dropped, which explains the big fall in total energy expenditure. To the scientists’ great surprise they discovered, instead, that basal metabolic rates (i.e. Yet this study found the exact opposite - if anything, people have become more active and burn more calories than in the 1980s. For starters, there is a widely held belief that the rise in obesity over the past four decades is, at least partly, caused by us becoming lazier, spending more time in front of screens and, therefore, burning fewer calories. You then collect urine samples and, with the help of some sophisticated maths, it is possible to estimate how many calories that person is burning during a normal day.įor the latest study in the journal Nature, the British and Chinese scientists looked at data that has been collected using this method on more than 4,000 people across the UK, U.S. You start by asking people to drink a special type of water, where the hydrogen and oxygen molecules have been replaced with naturally occurring ‘heavy’ forms. Scientists measure TEE using the ‘doubly labelled water’ method.

Mosley little green