24 November 2010

Dietary recommendations no cure for obesity

Dietary recommendations and obesity

If you want to lose weight or avoid gaining weight, you should cut down on finely refined starch calories such as white bread and white rice and instead eat a diet that is high in proteins with more lean meat, low-fat dairy products and beans. This is the result of a new extensive European diet study headed by researchers from University of Copenhagen. The study thereby confronts the official dietary recommendations and concludes that they are not sufficient for preventing obesity.

Fat personEat fruit, vegetables and fish and go easy on the fat. Eat a balanced diet and maintain a normal weight. These are some of the official dietary recommendations in Europe, including Denmark. Now researchers from Faculty of Life Sciences (LIFE) at University of Copenhagen have demonstrated that the dietary recommendations are not sufficient to prevent obesity. The results have just been published in the distinguished New England Journal of Medicine.

The world's largest diet study

A total of 772 families, comprising 938 adult family members and 827 children, participated in the European Diogenes diet study. This makes it the largest controlled random study in the world. The study was conducted by eight European research centres. The objective of the study has been to compare the official dietary recommendations in Europe, including the Danish recommendations, with a diet based on the latest knowledge about the importance of proteins and carbohydrates for appetite regulation.

- The Diogenes study shows that the current dietary recommendations are not good enough to prevent overweight persons from gaining weight. If you are to maintain your weight or avoid regaining weight after slimming, you must choose the right diet type, explains Associate Professor Thomas Meinert Larsen, PhD, from Department of Human Nutrition, LIFE at University of Copenhagen who has headed the Diogenes study together with Professor Arne Astrup, DrMedSc and Head of Department at LIFE.

A close look at the five diet types

The 938 overweight adults initially followed an 800 kcal/day diet for eight weeks, losing an average of 11 kg. They were then randomly assigned to one of five different low-fat diet types which they followed for six months in order to test which diet was most effective at preventing weight regain. Throughout the project, the families received expert guidance from dieticians and were asked to provide blood and urine samples.

The five different diet types (see box with facts) which the participants tested were characterised by different protein contents and differences in the so-called glycemic index (GI). GI is a measure of the ability of carbohydrates to increase blood glucose levels when absorbed in the body. Food with a low-glycemic index (LGI) causes blood glucose levels to increase more slowly and to lower levels compared to high-carbohydrate foods with a high glycemic index.

A high-protein, low-GI diet works best

Of the 938 adult participants, 548 completed both the initial weight-loss phase and the subsequent six-month diet intervention where they were assigned to different diet types. The average weight regain among the participants was 0.5 kg but there were significant differences from diet type to diet type.

- The group on the high-protein diet with a low glycemic index were the only ones that maintained their weight after the initial 11 kg weight loss and thus did not regain weight. In comparison, those in the low-protein/high-GI group showed a weight gain of 1.67 kg, says Thomas Meinert Larsen.

- We also noted that fewer participants in the high-protein, low-GI group dropped out of the project than in the low-protein, high-GI group. This may be due to a low-GI diet resulting in slow digestion and thus more stable blood glucose levels so that you feel good. Also, proteins result in greater satiety than carbohydrates and fat so that they did not feel hungry, explains Thomas Meinert Larsen.

Overweight children lose weight without going on a diet

In the families, there were 827 children who only participated in the diet intervention. Thus, they were never required to go on a diet or count calories - they simply followed the same diet as their parents. Approx. 45% of the children in these families were overweight.

- We saw that in the group of children who maintained a high-protein, low-GI diet, the prevalence of overweight dropped spontaneously by approx. 15% in just six months. This is remarkable because the children were not on a slimming diet or counting calories. The families just changed their diet. This gives hope that we can prevent child obesity by just making the children eat a slightly different diet, says Professor Arne Astrup.

The results of the children's study have been published in a separate article in the American medical journal Pediatrics.

The promising results make the researchers continue their efforts to make the new diet composition a natural part of the Danes' dietary habits.

-This fits in nicely with the work we are already doing in connection with developing the New Nordic Diet, says Arne Astrup.

Raw and cold food is good

Healty foodWhen it comes to the recommendations that you should eat plenty of fruit and vegetables, low-fat foods, plenty of fibre and limit your sugar intake, the new research results are in line with the official dietary recommendations. But this is not sufficient if you want to maintain your weight.

- Our diet study shows that, for instance, the dietary recommendation to eat six servings of fruits or vegetables a day is too undifferentiated. Because according to our study, some fruits can be eaten freely whereas the intake of others should be limited. And vegetables such as carrots, beets and parsnip should preferably be eaten raw, says Thomas Meinert Larsen.

Potatoes, the national staple food in Denmark, should be cooked as little as possible. Therefore, new potatoes are particularly good and it is a good idea to eat them cold. The same goes for pasta which should be cooked ‘al dente' and preferably eaten cold.

- This is due to the chemical structure of the carbohydrates changing when cooled down. Therefore they are broken down more slowly in the intestines which ensures more stable blood glucose levels, explains Thomas Meinert Larsen.