Putting it all together: Meta-analyses
Of course, it’s important to keep in mind that, while these three trials have revealed some of the best evidence yet about weight loss strategies, countless smaller or shorter clinical trials have focused on diet and weight loss. To truly get a sense of the state of the field of research, scientists look at many studies together, in a type of study called a meta-analysis. This type of research can be especially valuable when looking at a number of smaller clinical trials because it reveals what the studies show when they are combined as a whole.
A meta-analysis lets researchers examine a large number of smaller studies to see if, collectively, there’s been an impact, Bray said. And when you do that with weight loss trials, you don’t come out with any notable differences between diets,
A 2014 meta-analysis, published in JAMA, looked specifically at named diets — for example, the Atkins diet, the Ornish diet and others — and found that both low-fat and low-carbohydrate diets resulted in weight loss. There were 48 studies included in the meta-analysis, and between the individual named diets, the differences in weight loss were small, according to the researchers.
Both low-fat diets and low-carb diets resulted in about 18 lbs. (8 kg) of weight loss after six months, according to the study.
And while there were some statistically significant differences in weight loss between some of the diets (for example, after six months, the Atkins diet was associated with a 3.7-lb. (1.7 kg) greater weight loss than the Zone diet), “these differences are small and likely to be unimportant to many seeking to lose weight,”
“The main takeaway [of the meta-analysis] is that there’s really no important differences between any of the diets,” said Bradley Johnston, the director of Systematic Overviews through advancing Research Technology at the SickKids Research Institute in Toronto and lead author of the meta-analysis.
Indeed, most of the diets that Johnston looked at seemed to come back to calories.
Whether people did low-carb or some other type of diet, most of them were calorie-restricted, Johnston told Live Science. “If you actually follow the diet, it’s highly likely that you’re going to lose weight,” he said.
What’s important is that people choose a diet that they can stick with.