Diet, predisposition and reward.

Overweight is a major health problem with serious co morbidities. Weight loss is usually achieved more readily than weight maintenance after body weight loss. Conditions for weight maintenance after weight loss are (a) sustained satiety despite negative energy balance, (b) sustained basal energy expenditure despite body weight loss, due to (c) sparing of fat-free mass, which is the main determinant of basal energy expenditure. Diets with a relatively high-protein content act on these metabolic targets (4). Increasing the relative protein content reduces food intake under ad libitum conditions, resulting in immediate body weight loss. In the long term, body weight reaches a new value at a significantly lower level. Thus, an increase in the relative protein content of the diet, irrespective of protein type, reduces the risk of a positive energy balance and the development of overweight. Increasing protein intake also increases the chance of maintenance of body weight after weight loss induced by an energy-restricted diet.
So the most successful diets are those with a relatively high-protein content. But compliance remains an issue with all diets. In the first place it will be assessed whether predisposition for overweight affects compliance and success; second, whether sensitivity for food-reward affects compliance and success.

Overweight is a major health problem with serious co morbidities. Weight loss is usually achieved more readily than weight maintenance after body weight loss. Conditions for weight maintenance after weight loss are (a) sustained satiety despite negative energy balance, (b) sustained basal energy expenditure despite body weight loss, due to (c) sparing of fat-free mass, which is the main determinant of basal energy expenditure. Diets with a relatively high-protein content act on these metabolic targets (4). Increasing the relative protein content reduces food intake under ad libitum conditions, resulting in immediate body weight loss. In the long term, body weight reaches a new value at a significantly lower level. Thus, an increase in the relative protein content of the diet, irrespective of protein type, reduces the risk of a positive energy balance and the development of overweight. Increasing protein intake also increases the chance of maintenance of body weight after weight loss induced by an energy-restricted diet.

So the most successful diets are those with a relatively high-protein content. But compliance remains an issue with all diets. In the first place it will be assessed whether predisposition for overweight affects compliance and success; second, whether sensitivity for food-reward affects compliance and success.

1. Baseline (before weight loss);

2. After 6 months of weight loss;

3. After 3 months of weight maintenance.

The study has a double blind parallel 2-arm design, with 2 conditions (diets). There are 2 different diets: one that is relatively high in protein and one with normal protein content. The subjects (n=300, BMI>25, age 18-55) first have a three-month period of weight loss during which they are on the same weight loss diet consisting of the commercially available meal substitute: modifast. This is followed by a six-month period of weight maintenance during which the subjects are randomized in 2 diet groups. Of the 300 subjects that complete the weight loss and weight maintenance, the polymorphisms of the TaqIA gene and the FTO gene are determined together with anthropometry measurements (body weight, body composition, waist-hip ratio and sagital diameter); of these 300, 88 will be assessed in the fMRI to investigate the brain areas involved in plasticity of reward with respect to food.
In total there are three measurement moments: before the weight loss, before the weight maintenance and after the weight maintenance at which anthropometry measurements are taken and the fMRI investigations are conducted. Compliance is determined by magnitude of weight loss.


Thus:

1. Weight loss using a commercial available meal substitute: modifast;

2. Weight maintenance during which the subjects are assigned to 1 of 2 diets: a relatively high protein diet and a diet with normal protein content.