The people in the study were assigned to counseling sessions to learn about their diets, and there were group sessions held throughout the course of the study. The researchers provided the participants with daily meal plans, and the plans were largely similar across the four diets, with only small tweaks — for example, to include a bit of extra olive oil, or a bit less meat. All of the diets in the study were healthy — they all contained healthy fats, whole grains, fruits and vegetables, said Sacks, who was the lead author of the study. And all of the diets contained an equal number of calories — fewer than the number of calories the people in the study were normally eating,
So, how did the different diets stack up for weight loss?
The main takeaway of the study is that all of the diets produced the same amount of weight loss, Sacks said. “There was no advantage of one diet type over another,” he said. The researchers observed that, at six months, the participants in each diet had lost, on average, 13.2 lbs. (6 kg). After the one-year mark, on average, the participants began to regain some of their weight. By the end of the study, the average weight loss for all of the diets was 8.8 lbs. (4 kg).
Bray, who ran the Baton Rouge arm of the study, noted that there was certainly a range for the weight loss observed among the people on each diet. However, the range was similar in all of the groups, he said. Some people on each diet lost as much as 33.1 lbs. (15 kg), and some people on each diet gained a bit of weight, Bray told Live Science. But even the proportions of people losing a lot of weight or gaining a little weight were similar in all four diets,
The biggest factor for weight loss? Undoubtedly, it was adherence to the diet, Bray said. “If you stuck to [the diet] well, you should lose more, and if you didn’t stick to [the diet], you shouldn’t,”