Extensive literature search and review as preparatory work for the evaluation of the essential composition of total diet replacement products for weight control
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For this review a comprehensive literature search was carried out to identify human intervention studies, which investigated the effect of differences in composition of low and very low calorie diets on adverse metabolic effects. We identified 2653 papers in PubMed, of which nine papers met our inclusion criteria. These included publications reported on different types of low calorie diets, including ketogenic and nonketogenic diets (n = 4), diets differing in content of macronutrients (proteins, fat and carbohydrates) and energy value (n = 2), a diet supplemented with pyruvate (n = 1) and diets supplemented with fatty acids (medium-chain triglycerides (n = 1) and omega-3 fatty acids (n = 1)). Only four of the nine publications investigated comparable diets. The main adverse health outcomes in the studies included ketosis (n = 7), metabolic acidosis (n = 1), muscle loss/protein sparing (n = 6), mood and cognition (n = 2), gallstone formation (n = 1), organ functioning (n = 2) and complaints (n = 3), and essential fatty acid status (n = 1). The evidence summarized in this review shows that a very low calorie ketogenic diet as compared to a very low calorie nonketogenic diet resulted in higher concentrations of ketone bodies. In one study mild acidosis was reported in the ketogenic diet group. In addition, in three studies, very low calorie nonketogenic diets showed to be superior to ketogenic diets in protein sparing during a period of 4 weeks. Gallstone formation was reported in one study comparing a low calorie diet with a very low calorie diet, and liver function was tested in three single studies on very low calorie diets, but results were inconclusive. Other frequent complaints that were mentioned in the studies included constipation, borborygmus, diarrhoea, dizziness, dry skin, cold intolerance and hair loss, but no statistical significant differences in occurrence were observed between intervention and control groups.