Atkins, Paleo or Zone – whichever diet you follow, you will only lose a bit of weight, and improvements to your blood pressure and cholesterol will disappear within a year.
That is according to a comparison of randomised clinical trials assessing the effects of 14 popular branded diets. “We chose the categories of diets that are most widely advertised and that are in the public mind,” says Gordon Guyatt at McMaster University in Canada, who led the research.
Guyatt and his colleagues found 121 trials of such diets, together including nearly 22,000 volunteers who were either overweight or obese, and had an average age of 49. Each trial compared the results of adults who were on the diet with others who ate as they usually did. The team looked for evidence of the diets’ effect on weight loss and markers of cardiovascular health, including blood pressure and cholesterol.
All of the diets resulted in some weight loss. Six months after starting a diet, volunteers were, on average, about 4 kilograms lighter. There were also improvements in blood pressure and cholesterol at this point: levels of harmful LDL cholesterol were lower, while there was more of the beneficial HDL form.
The team noted some small differences in the effects of the diets. The Mediterranean diet appeared to have the biggest impact on cholesterol, for example, and low-fat diets also improved cholesterol to a greater degree than other diets. The Atkins diet seemed to result in the most weight loss at six months.
But 12 months into a diet, the effects had mostly disappeared. By this point, the volunteers had gained back most of their lost weight, and the benefits relating to blood pressure and cholesterol had vanished.
“People can lose appreciable amounts of weight in the short term, and weight loss is associated with a decrease in risk factors,” says Guyatt. “However, with time, people tend to gain the weight back, and in 12 months there’s no benefit in terms of blood pressure and cholesterol.”
Long-term benefits unclear
Volunteers may have struggled to maintain their diets, says Guyatt. “The fact that they lost weight early and much of it was regained suggests that adherence to the diet was much better in the first six months,” he says.
While the team was able to look at markers of cardiovascular health, it isn’t clear what these temporary changes in blood pressure and cholesterol mean for a person’s health in the long run. We don’t know if following one of these diets might lower a person’s risk of having a heart attack, stroke or early death, for example.
But as there are some short-term benefits, any of the diets might be useful for someone looking to lose weight. “Since it really doesn’t matter which diet you use, you should pick the diet most appealing to you,” says Guyatt. “The biggest challenge you’ll face is to maintain the diet.”
Journal reference: BMJ, DOI: 10.1136/bmj.m696
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