Summary

The Mediterranean, low-fat, and low-carbohydrate approaches all produce weight loss, according to a new two year study. The Mediterranean approach also has specific benefits for people with diabetes. And the low-carb diet is best at improving cholesterol profile.

Introduction

People can get very confused when it comes to choosing the best approach to weight loss - not least because there is just so much information out there. And we also know that people do not often stick to a diet and often put any weight lost back in the long-term. There has been a lack of good clinical trials to address the issue of how effective different diets are in both weight loss terms and also with respect to other factors like cholesterol and blood glucose levels. Researchers in Israel, Germany and the USA now report on the two year Dietary Intervention Randomized Controlled Trial (DIRECT) which compares Mediterranean, low-fat and low-carbohydrate diets.

What was done

A group of 322 moderately obese participants, average age 52 years of whom 85 percent were men, were assigned randomly to one of three diets: Mediterranean, low-fat or low-carb. The Mediterranean diet was moderate in fat and restricted in calories. It was rich in vegetables and low in red meat. Poultry and fish replaced beef and lamb. Calorie intake was restricted to 1500 kcal per day for women, 1800 kcal per day for men, and fat provided no more than 35 percent of calories. The main sources of added fat were 30 to 45 grams of olive oil and just a handful of nuts a day.

The low-fat diet was that based upon American Heart Association guidelines, with the same calorie limits as the Mediterranean diet. No more than 30 percent of calories came from fat, including ten percent from saturated fat. The diet was based upon low-fat grains, vegetables, fruits and legumes. Intake of additional fat, sweets and high-fat snacks was strictly limited. The low-carb diet aimed to provide just 20 grams of carbohydrate a day for the first two months with an increase to 120 grams over time. Total intake of calories, protein and fat were not limited. However, participants were advised to go for vegetarian sources. Participants were weighed each month. Blood pressure, fasting glucose, cholesterol and other biomarkers were also measured.

What was found

Drop out rate in this trial was pleasingly low - at 12 months, 95 percent were still on board and the figure had dropped to 85 percent at two years. All groups lost some weight - with the Mediterranean and low-carb diets being more effective. The overall weight losses at the end of the trial were 2.9 kilograms for the low-fat group, 4.4 kilograms for the Mediterranean group and 4.7 kilograms for the low-cab group. All three groups had significant decreases in both waist circumference and blood pressure, but there were no significant differences between groups in this respect.

HDL (high density lipoprotein or "good") cholesterol levels increased in all groups, with the greatest increase being seen in the low-carb group. Thirty six of the participants had diabetes and those who were in the Mediterranean group had a significant decrease in their fasting glucose levels.

What this study means

Three significantly different approaches to weight loss all work - so there is no one way of tackling an overweight problem. This is good news because it means people can make an informed choice. Those who don't want to bother with calorie restriction can go for the low-carb approach and eat as much (vegetarian) fat and protein as they want. Choice of a weight loss diet could also be tailored towards an individual's needs - those with diabetes could lower their glucose with the Mediterranean approach and those who need to lower their cholesterol might go for the low-carb diet.