Differences between popular diet programs “small to trivial,” study says

Most popular diet programs result in similar modest weight loss and improvements in cardiovascular risk factors over a period of six months, according to a new study published in The BMJ.

Obesity has nearly tripled worldwide since 1975, prompting a plethora of dietary recommendations for weight management and cardiovascular risk reduction. So far, there has been no comprehensive analysis comparing the relative impact of different diets for weight loss and improving cardiovascular risk factors, such as blood pressure and cholesterol levels.

To address this, a team of international researchers set out to determine the relative effectiveness of dietary patterns and popular-named diets among overweight or obese adults. They reviewed the results of 121 randomized trials with 21,942 patients with an average age of 49 years old who followed a popular diet or an alternative control diet and reported weight loss, and changes in cardiovascular risk factors. The studies were designed differently, and were of varying quality, but the researchers were able to allow for that in their analysis.

They grouped diets by macronutrient patterns and according to 14 popular named dietary programs. Compared with a usual diet, low carbohydrate and low-fat diets resulted in a similar modest reduction in weight, between 8 and 11 pounds, and reductions in blood pressure at six months. Moderate macronutrient diets resulted in slightly less weight loss and blood pressure reductions.

Among popular named diets, the Atkins, Dietary Approaches to Stop Hypertension (DASH), and Zone diets had the largest effect on weight loss, between 7 and 12 pounds, and blood pressure compared with a usual diet at six months. No diets significantly improved levels of high-density lipoproteins cholesterol or C-reactive protein, a chemical associated with inflammation, at six months.

Overall, weight loss diminished at 12 months among all dietary patterns and popular named diets, while the benefits for cardiovascular risk factors of all diets, except the Mediterranean diet, disappeared, according to the study.

The researchers point to some study limitations that could have affected the accuracy of their estimates but say their comprehensive search and thorough analyses supports the robustness of the results.

For short-term benefits, the researchers suggest that people should choose the diet they prefer without concern about the size of benefits.