Calories, not protein or carbs, are key to weight loss for people with diabetes

The study, led by endocrinologist Dr Jeremy Krebs, has just been published in the international diabetes research journal Diabetologia.

It looked at whether 419 participants (aged 35-75) in Auckland, Wellington and Christchurch had different rates of weight loss over two years when they were given two low fat diets; one involving high protein intake and the other high in carbohydrates.

"We decided to do this study as weight loss is very important in terms of control of blood sugar levels and many people with diabetes are seriously overweight. However there has been a lot of medical and public debate about the best way to achieve this, and which diets may be the most effective over the long term," says Dr Krebs.

Dr Krebs says there has been widespread publicity about low carb/high protein diets such as the 'Dr Atkins diet revolution' and 'The Zone' diet, with evidence of short term weight loss, but no difference to other diets over 12 months. He says the critical factor is to achieve weight loss over the long term, not just in six months or a year.

The two groups of moderately overweight people with diabetes (BMI above 27) were prescribed the specific diets supported by 18 group sessions with a dietitian, while also using food diaries to track their eating and weight loss progress.

The final results showed that there was no significant difference in weight reduction between the low fat/high protein and low fat/high carbohydrate diets after two years of the study. Both groups lost weight which was related to the total calorie intake going down with the low fat diets, indicating this was the driving factor in weight loss.

"We certainly did achieve a modest weight loss, of two to three kilos, in both groups, but essentially there was little difference between the two diets," says Krebs.

"This confirms that the solution to weight loss over the long term is reducing energy intake; that is the amount of calories someone eats on a daily basis."

Dr Krebs also says that outside the issue of total calorie intake the study suggests that flexibility in adopting the type of diet to follow is the best approach to reducing weight. This still needs to recognize that saturated fat is harmful and fibre is extremely important.

"Many people have real difficulty following one type of diet over the long term. It is just so hard. In our study 30% of the original participants dropped out because they couldn't maintain the diet they were prescribed."

"Even those who stuck to the diet, more or less, did not reach the level of protein or carb intake recommended by the study over the two year period, which shows how difficult it is for people to change from their habitual diet."

Dr Krebs says it is well known that increased diabetes rates and excess weight are huge health problems in New Zealand which are costing the health system hundreds of millions of dollars a year.

This study shows that substituting fat with high protein is no better than high carbohydrate in promoting weight loss. Allowing patients to choose which approach suits them best whilst focusing on reducing total energy intake may be the best solution.

"Often people drift back to their old eating habits and the behaviour of many participants in this study also illustrated this tendency. The real key to obesity in people with type 2 diabetes, and to better blood sugar control, is to focus on cutting calorie intake over the long term," he says.

The study was funded by the Health Research Council.

Provided by University of Otago