Fat fight: researchers disagree over study into low-fat diets

A row has broken out between researchers over claims made in a new study that adopting a low-fat diet may not be the best way to slim.

US experts who analysed data on more than 68,000 adults concluded that curbing fat intake did not lead to greater weight loss than low-carbohydrate or Mediterranean diets.

The scientists pulled together information from 53 trials comparing the ability of low-fat and other kinds of diet to shed unwanted pounds over a period of at least one year.

They found no significant difference in average levels of weight loss between reduced-fat and higher-fat diets.

Diets that cut out fat were actually slightly less effective than those based on lowering carbohydrate consumption, the researchers reported in The Lancet Diabetes & Endocrinology medical journal.

Compared with not dieting at all, avoiding fat resulted in 5.4 kilograms being shed after a year, while low carbohydrate diets added another 1.15 kilograms of weight loss.

Lead scientist Dr Deirdre Tobias from Brigham and Women's Hospital and Harvard Medical School in Boston, US, said: "There is no good evidence for recommending low-fat diets.

“Behind current dietary advice to cut out the fat, which contains more than twice the calories per gram of carbohydrates and protein, the thinking is that simply reducing fat intake will naturally lead to weight loss. But our robust evidence clearly suggests otherwise.”

However, Dr Tobias was strongly challenged by leading British nutritionist professor Susan Jebb, from Oxford University, who took issue with a press release headline describing low-fat diets as "ineffective".

“Weight losses of 5kg may be less than many people might hope for but we know from many other research studies that this brings surprisingly large health benefits, more than halving the risk of developing diabetes in people with raised blood sugar,” professor Jebb said.

“These benefits are attenuated but not lost if weight is regained. Inaccurate reports that dieting is ‘ineffective’ undermine public confidence and deter health professionals from encouraging and supporting people who are overweight to lose weight.”

Professor Tom Sanders, another nutrition expert from King's College London, said: "It is not surprising that the diets focusing on restricting carbohydrate intake led to slightly greater weight loss, as carbohydrate typically supplies 45-50 per cent of the energy intake. It is easier to reduce energy intake by cutting back on the amount of bread, potatoes and rice in the diet."

He stressed that most diet studies failed to deliver meaningful results because participants are so bad at following dietary instructions.

“To me the take home message from this paper is that energy intake determines the extent of weight loss rather than the relative proportions of fat and carbohydrate in the diet,” Prof Sanders added.

“In order to control body weight, it still remains sensible advice to eat less and avoid consuming excess amounts of fat and sugar especially as fatty meat, deep fried foods, cakes and biscuits and sugar-sweetened beverages.”

PA