But a recent study, published in Cell Metabolism, has found that reducing fat intake leads to greater body fat loss. The study was carried out by researchers from the US National Institutes of Health and was funded by the same organisation.
The study – after a new diet lab rigorously enforced either a six-day low fat or low carb diet for 19 obese men and women – revealed that the low fat diet led to more fat loss – the outcome the study was most interested in – but the low carb diet led to more weight loss overall.
So while cutting carbs may lead to greater fat burn, more body fat is lost during the low-fat dietary period.
Clearly not all calories are created equal when it comes to body fat loss.
“There is one set of beliefs that says all calories are exactly equal when it comes to body fat loss and there’s another that says carbohydrate calories are particularly fattening, so cutting those should lead to more fat loss,” states Hall. “Our results showed that, actually, not all calories are created equal when it comes to body fat loss, but over the long term, it’s pretty close.”
Both diets led to weight loss over the six days, but those on the low carb diet lost significantly more. After six days, the low carb group lost about 1.85kg on average compared with around 1.3kg in those on the low fat diet – a difference of half a kilo in just six days.
The low-carb diet created significant changes in metabolic fuel selection. Insulin levels dropped, leading to lower carbohydrate burning by around 500 calories a day and increased fat burning by around 400 calories a day.
The low fat diet, on the other hand, resulted in a greater body fat loss compared with the low-carb diet, despite being equivalent in calories.
The research proved that “calorie for calorie, restriction of dietary fat led to greater body fat loss than restriction of dietary carbohydrate in adults with obesity”. The study rejects the claim that carbohydrate restriction is required for body fat loss, adding that fat loss is a more important goal than weight loss in the treatment of obesity.
However, the results of just one small study may not be convincing enough to settle the low fat versus low carb diet debate.
But all that is inside the diet lab. In the outside world, diet adherence is likely the most important determinant of body fat loss”.
As Professor Susan Jebb, Professor of Diet and Population Health at the University of Oxford, has said: “The real challenge for science is not the nutritional composition of the diet, but the behavioral strategies to promote adherence.”
So low carb or low fat? The best diet for weight loss is the diet you can stick to!