New York, Most diets lead to weight loss and improvements in cardiovascular risk factors but the results may disappear within a year, say researcher, suggesting that people should choose the diet they prefer without concern about the size of benefits.

Published in the journal The BMJ, the research found that in most diets, weight reduction at the 12-month follow-up diminished, and improvements in cardiovascular risk factors largely disappeared -- except in association with the Mediterranean diet, which saw a small but important reduction in ‘bad' LDL cholesterol.

To reach this conclusion, the International team of researchers set out to determine the relative effectiveness of dietary patterns and popular named diets among overweight or obese adults.

The findings are based on the results of 121 randomised trials with 21,942 patients (average age 49) who followed a popular named diet or an alternative control diet and reported weight loss, and changes in cardiovascular risk factors.

They grouped diets by macronutrient patterns (low carbohydrate, low fat, and moderate macronutrient - similar to low fat, but slightly more fat and slightly less carbohydrate) and according to 14 popular named dietary programmes (Atkins, DASH, Mediterranean, etc).

Compared with a usual diet, low carbohydrate and low-fat diets resulted in a similar modest reduction in weight (between four and five kg) 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, Atkins, DASH, and Zone had the largest effect on weight loss (between 3.5 and 5.5 kg) and blood pressure compared with a usual diet at six months. No diets significantly improved levels of 'good' HDL 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, essentially disappeared.

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

Evidence shows that most macronutrient diets result in modest weight loss and substantial improvements in cardiovascular risk factors, particularly blood pressure, at six but not 12 months.

The extensive range of popular diets analysed "provides a plethora of choice but no clear winner," the researchers noted.