Is the success of protein diets related to predisposition of overweight and sensitivity for food-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.

To asses whether the success of protein diets is related to predisposition of
overweight and sensitivity for food-reward

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.

Weight loss using a commercial available meal substitute: modifast.
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

This research is neither beneficial nor harmful to the subjects. fMRI is a
non-invasive standard brain-imaging method without any significant risks (See
chapter K4A for standardized and approved methods for conducting fMRI
experiments involving human subjects). It is a technique that utilizes magnetic
fields and low energy radio frequencies to visualize brain structures and brain
function. During screening subjects with metallic fragments in their body will
be excluded from the study since the fMRI magnet exerts a force on
ferromagnetic objects. The blood sampling in this study does not include any
other risks for the subjects, apart from its usual risk of minor bruising.