A quick glance at the health section of any bookstore will reveal a bewildering array of different approaches to weight loss, but it looks like one of the most popular options for dieters isn't all that effective in the long run if you want to shed some excess baggage.
A broad study analysing the dietary practices of more than 68,000 adults has found that low-fat diets are ineffective for achieving long-term weight loss. After a year, low-fat diets are ultimately either comparable or less effective than other kinds of dietary interventions of similar intensity, such as higher-fat diets, including low-carbohydrate diets and Mediterranean diets.
"There is no good evidence for recommending low-fat diets," said Deirdre Tobias, a doctor from Harvard Medical School and lead author of the study. "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."
The researchers conducted a meta-analysis of 53 separate studies involving 68,128 adults – in essence, all the relevant randomised trials up until July 2014 comparing the effectiveness of low-fat diets with other types of diets.
They found that low-carb diets led to greater weight loss than low-fat diets in the long term (after one year), but the difference between the two was small – just 1.15 kilograms. Other kinds of higher-fat dietary interventions were also found to be superior to low-fat diets, but the advantage was so small it wasn't considered statistically significant (just 0.36 kg).
In other words, if you want to lose weight, you don't need to commit to low-fat cheese and zero dessert. Foods that are higher in fat including meat and dairy products can also be part of a healthy weight-loss diet – provided you keep an eye on your overall energy intake.
About the only good thing that can be said for low-fat diets is that they're a more effective strategy than having no kind of restricted diet plan at all. Committing to a low-fat diet did see people losing an average of 5.41 kg compared to people who just ate their regular diet.
But the real takeaway from the study might not just be that low-fat diets are ineffective when it comes to keeping weight off in the long term. The results suggest that 'diets' as a whole aren't particularly effective at helping you lose and keep the weight off. After all, even the best-performing diet analysed - low-carb - didn't achieve a particularly impressive result after a year, and across all types of diets the researchers investigated, the average weight loss after 12 months was just 3.75 kg.
"[B]efore proclaiming the superiority of low-carbohydrate diets for the treatment of obesity, consider the magnitude of the benefit: participants prescribed low-carbohydrate diets lost only about 1 kg of additional weight after 1 year compared with those advised to consume low-fat diets," writes Kevin D Hall of the US National Institute of Diabetes and Digestive and Kidney Diseases, in a commentary on the research.
"Although statistically significant, such a minuscule difference in weight loss is clinically meaningless. Furthermore, irrespective of the diet prescription, the overall average weight loss in trials testing interventions designed to reduce bodyweight was unimpressive."
The question then – and one which applies to every kind of weight-loss regimen that doctors and dieticians recommend to their patients – is how to manage poor adherence to diets in the long term, since dieters tend to reach their peak in weight loss at the six- to eight-month mark before relapsing into old habits.
"Much more research is needed to determine the factors that affect diet adherence and thereby help maintain weight loss over the long term," writes Hall. "What seems to be clear is that long-term diet adherence is abysmal, irrespective of whether low-fat or other diets, such as low-carbohydrate diets, are prescribed."
The findings were published in The Lancet Diabetes & Endocrinology.