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Background - Although several studies have shown that an early adiposity rebound (AR) is associated with an increased risk of adult obesity, it is not clear whether the rebound in body mass index (BMI) is actually attributable to changes in body fat. Objective - To determine the changes in body composition occurring in girls during AR. Design - Body composition was measured using dual-energy x-ray absorptiometry (DXA) at baseline, year one, year two and year four in 40 girls aged 3-6 years at baseline. Dietary intake was estimated by four-day diet records and physical activity by questionnaire. Age at AR was determined by modelling. The velocity of change (% per year) in height, weight and fat and lean tissues was estimated for each subject using random coefficient models. Early AR was defined as less than five years of age and late AR as five or more years of age. Outcomes - Early and late rebounders did not differ in age, height, weight, body composition, dietary protein intake or physical activity participation at baseline. Although height velocity was similar, weight velocity was significantly higher in early compared with late rebounders (13.5% vs 10.7, P<0.001). Differences in weight velocity were entirely due to change in body fat stores; early rebounders gained body fat at more than twice the rate of late rebounders (17.1 vs 6.5%, P<0.001) whereas no differences were observed in lean mass velocity. By the age of 9 years, girls with an early AR were more than 4 kg heavier than girls with an early AR, with considerably more body fat and a greater percentage classified as overweight. Conclusions - Our study demonstrates that the differences in BMI during AR are due specifically to alterations in body fat and not to alterations in lean mass or height. [ABSTRACT FROM AUTHOR]

Background -- Low-carbohydrate, high-fat weight loss diets do not increase plasma cholesterol concentrations despite being high in saturated fat and cholesterol. Objective -- To determine if the dissociation that occurs between dietary fat and plasma cholesterol during high saturated fat weight loss diets is related to the lack of effect of these diets on plasma fatty acid composition. Design -- Ninety six women were randomised to follow one of three weight loss diets for two months; a high-carbohydrate, low-fat diet (HC), a high-protein diet (HP), or a low-carbohydrate, high-fat diet (HF). Results -- Mean energy intake in all three groups was 1.5 to 2.0 MJ/d lower during the weight loss period than before. During the weight loss period fat made up 57, 35 and 25 percent of energy (%kJ) in the HF, HP and HC groups, respectively, of which 22, 11, and 8 %kJ was saturated fat. Mean weight loss in the HF (6.4 kg) and HP group (5.5 kg) was significantly greater (P<0.05) than in the HC group (4.3 kg). Fasting plasma total cholesterol concentration decreased in the HC and HP but remained unchanged in the HF group. The changes in fatty acid composition of plasma triacyglycerol did not differ between the three diet groups. Myristic acid (C14:0) and palmitic acid (C16:0) composition decreased whereas oleic acid (C18:1n-9) and linoleic acid (C18:2n-6) increased. Conclusion - During weight loss the fatty acid composition of plasma does not reflect dietary fat intake. We speculate that most dietary fat is oxidised during weight loss and that plasma fatty composition quickly reflects endogenous stores or synthesis. This might explain why high-fat high-saturated fat weight loss diets do not increase plasma cholesterol. [ABSTRACT FROM AUTHOR]