Which weight loss diet works best? 4 popular diets compared

A study conducted by Dansinger et al., published in the Journal of the American Medical Association in 2005
(vol 293, no.1 Jan 5) compared adherence rates and the effectiveness of 4 popular diets (Atkins, Zone, Weight Watchers, and Ornish) for weight loss and cardiac risk factor reduction. 160 overweight/obese people aged 22-72 years (average age 50) were randomly assigned to one of the diets (i.e 40 subjects per diet).

The primary outcome of weight loss at 1 year was modest (about 5 kg for those who stuck to any of the diets) and there was no difference between the low carbohydrate high fat approach of Atkins, the high protein low glycaemic load approach of the Zone diet, the very low fat diet approach of Ornish and the low calorie portion size approach of weight watchers.

Adherence rates were poor for all 4 diets, especially for the more extreme Atkins and the Ornish diets; 42% of all participants were not following their diet after 12 months.

Interestingly, average energy intake was around 2000kcal before subjects were allocated to a diet; energy intake dropped to about 1500kcal on average in the first 6 months and crept up to 1800kcal in the last 6 months for all diets. At 1 year, mean energy reduction from baseline was around 200kcal for all diets.

Once participants were on their diet, the thing the made the biggest difference to weight loss was the amount of exercise they were doing. All participants were encouraged to do at least 60min of exercise per week. Exercise levels increased modestly from baseline throughout the trial and to a similar extent for each diet group.

Heart risk factor benefits were similar for all 4 diets i.e each diet significantly reduced LDL (bad) cholesterol and increased HDL (good) cholesterol (except the Ornish diet) to the same degree with no significant effects on triglycerides, blood pressure or fasting blood glucose at 1 year.

HEC commentary: At present, there are no data to help clinicians practicably match a diet to a patient's
"diet response genotype". For example, if you have the genetic make-up to develop diabetes then a low carbohydrate load low glycaemic index diet may be more effective than a high carbohydrate diet.
Furthermore, this study suggests that the macronutrient mix is not so important for weight loss - reducing energy intake by about 200-300kcal per day (easily achieved by reducing indulgences in the diet) and increasing energy expenditure through modest exercise (30min walking daily) should result in modest weight loss after 12 months (about 5kg) or at least weight maintenance. The best diet is to include ample vegetables, fruit, wholegrain cereals, nuts, legumes, reduced fat dairy products, seafood, lean meat and added 'good' fats in moderation.

Different weight loss diets compared: total calorie intake more important than amount of fat, protein and carbohydrates
Sack and colleagues reported in the New England of Journal of Medicine in February 2009 that reduced-calorie diets result in clinically meaningful weight loss regardless of which macronutrients they emphasize in 811 healthy overweight adults. They compared the following diets: low fat versus high fat; average protein versus high protein and high versus lowest carbohydrate diet. Each participant's caloric prescription represented a deficit of 750 kcal per day from baseline, as calculated from the person's resting energy expenditure and activity level. Satiety, hunger, satisfaction with the diet, and attendance at group sessions were similar for all diets. After 6 months, all groups had lost 6kg and had similar improvements in blood pressure, blood lipids and reduction in fasting insulin levels (except for the highest carbohydrate diet). The authors conclude"diets that are successful in causing weight loss can emphasize a range of fat, protein, and carbohydrate compositions that have beneficial effects on risk factors for cardiovascular disease and diabetes - such diets can also be tailored to individual patients on the basis of their personal and cultural preferences and may therefore have the best chance for long-term success". Please note, however, that these participants did not have diabetes and therefore problems with carbohydrate handling - the results may have been different if people with diabetes had been studied.

Further reading: HEC diet pyramid

Last Updated: March 2009