There are numerous studies on effects of therapeutic measures for overweight and obese persons (e.g., [1]). Nevertheless, proof of long-term effectiveness is often not provided [2]. Particularly with regard to commercial diet programs, accurate information about weight loss is rarely available [3]. Many studies can be interpreted and generalized to a limited extent only, either because the size of the sample is too small, the dropout rate is too high, or adherence to the diet is not registered [4].
Numerous studies deal with the—still controversial—issue which form of diet would be optimal for treating the overweight and obese [5–9]. Various studies showed that, in the medium term at least, lowcarbohydrate, high-protein diets led to a greater weight loss than low-calorie, low-fat diets [10, 11], though other studies did not yield the same results [12, 13]. Sacks et al. [14] found that the form of the diet had less influence on the success of a weight reduction program than adherence to it and regular contact with the therapist. As short-termtherapy plans offer initial success, which is frequently followed by a renewed increase in weight, any therapy aiming at weight loss must meet the criterion of being effective in the long run….