May 2009
Newsletter from Dr David Ashton
Medical Director, Healthier Weight
Hello!
A little taste of summer sunshine and the magazines are full of diets and promises for beach beautiful bodies. With so much "noise" and junk science, it is very difficult for people to sort the wood from the trees. Well, I can assure you that all you need to read is this prestigious study to convince you that it doesn't matter what kind of diet you do as long as you eat fewer calories than you expend.
A recent study evaluating the long-term (2 year) weight reducing efficacy of different types of diets – including low carbohydrates – concluded – yet again - that it is the reduction in calories NOT the composition of the diet that matters.
Background
In the study performed at Harvard School of Public Health, Boston, USA, researchers randomly assigned 811 overweight adults to one of four diets, each containing different amounts of fat and protein, with a graded reduction in carbohydrate intake. The diets consisted of similar foods and met guidelines for cardiovascular health. In addition to the low-calorie diet, the study participants were offered group and individual instructional sessions for 2 years. The main outcome was the change in body weight after 2 years for each of the four diets.
Results
At 6 months, participants assigned to each diet had lost an average of 6 kg, which represented 7% of their initial weight; they began to regain weight after 12 months. By 2 years, weight loss remained similar in all groups, irrespective of the relative amounts of fat, protein and carbohydrate in the diet. Among the 80% of participants who completed the trial, the average weight loss was 4 kg and approximately 15% of the participants had a reduction of at least 10% of their initial body weight. Satiety (sense of fullness), hunger, satisfaction with the diet, and attendance at group sessions were similar for all diets; attendance was strongly associated with weight loss (0.2 kg per session attended). The diets improved risk factors such as cholesterol levels and insulin levels. The investigators concluded that it is the overall calorie intake that matters in weight reduction, regardless of the relative proportions of which macronutrients they emphasize.
Comment
This is a large and well conducted study from one of the most influential nutritional groups in the world and published in the prestigious New England Journal of Medicine. The results of this trial confirm what most experts already knew; that what produces weight loss has nothing to do with a specific level of carbohydrate (or indeed protein or fat), but is simply a function of the number of calories. The less you take in the more you lose. In addition, ketosis – still something promoted by some – is now regarded by most professionals as outdated, unnecessary and potentially harmful. The simple message is that to be successful in losing weight you need to reduce your total calorie intake and increase your calorie output through physical activity. Now where have I heard that before….?
Dr David Ashton MD PhD, Medical Director, Healthier Weight Centres
Ref: Sacks FM, Bray GA, Carey VJ, et al. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates.N Engl J Med 2009; 360:859-73
