For losing weight, does it matter whether I cut fat or cut carbs?

Nina TeicholzPhD · investigative science journalist and author

Cut carbs. In head-to-head trials the low-carbohydrate arm has nearly always lost more.

What it rests onThe low-fat preference rests on a 1970s hypothesis about fat's nine calories per gram. Multiple large long-term controlled experiments could not confirm that a low-fat diet produced significant weight loss, and in head-to-head trials with low-carbohydrate diets the latter "have nearly always led to more weight loss". She adds that low-fat diets reliably lower HDL cholesterol and raise triglycerides, and that the US Dietary Guidelines quietly dropped "low-fat" from their recommendations in 2015 without telling the public.

Christopher D. GardnerPhD · nutrition scientist, Stanford Prevention Research Center

Neither. Once both diets exclude added sugar and refined grain, the macronutrient split stops deciding the outcome.

What it rests onA 12-month randomised trial in 609 adults comparing a healthy low-fat with a healthy low-carbohydrate diet, both built under deliberate equipoise, produced median weight changes of 5.3 kg and 6.0 kg with no significant difference, and neither a prespecified genotype pattern nor baseline insulin secretion moderated the result. He concedes a small behavioural edge to low-carbohydrate eating (gar-lowcarb-edge) and locates it in cheating patterns rather than metabolism. His own 2007 A TO Z trial found the Atkins arm lost the most weight and he has never withdrawn it (gar-lowcarb-legitimate).