Obesity phenotypes can be regarded as an indicator of CVD risk factors. The aim of the present study was to determine the prevalence of adolescents with different obesity phenotypes and the role of obesity phenotypes in prediction of the metabolic syndrome (MetS) in adults. For this population-based cohort study, 2159 adolescents aged 11–18 years were included. Subjects were divided into four obesity phenotype groups: metabolically healthy normal weight (MHNW), metabolically healthy obese (MHO), metabolically unhealthy normal weight (MUNW) and metabolically unhealthy obese (MUO). Cox proportional hazard modelling was used to estimate the incidence of the MetS in adults after a median follow-up of 11·3 years. The incidence rate of the MetS in early adulthood was 111·6 (95 % CI 98·7, 126·3) per 10 000 person-years, with higher values in boys (210·1 (95 % CI 183·0, 241·3)), compared with girls (39·7 (95 % CI 30·2, 52·1)). In the age- and adult BMI-adjusted model, the hazard ratio of the MetS in adulthood for boys was 3·33 (95 % CI 2·08, 5·32) among MUO phenotype followed less than 6 years, 1·71 (95 % CI 1·01, 2·90) among MHO, and 2·52 (95 % CI 1·72, 3·68) among MUNW. All associations were attenuated in girls except for MUO phenotype followed less than 6 years (5·72 (95 % CI 2·14, 15·3)). In conclusion, MUNW and MHO phenotypes in boys, but not in girls, and MUO phenotype in both sexes with less than 6 years of follow-up increased the risk of adult MetS compared with MHNW. It seems that lack of obesity at least in boys does not protect them from MetS development in adulthood.

Randomised controlled trials comparing low- v. high-fat diets on cardiometabolic risk factors in people with overweight or obesity have shown inconsistent results, which may be due to the mixed metabolic status of people with excess adiposity. The role of dietary fat manipulation in modifying cardiometabolic indicators in people with overweight or obese without metabolic disturbance is unclear. Thus, meta-analysis was conducted to compare low- v. high-fat diets on cardiometabolic indicators in people who are overweight or obese without metabolic disturbance in the present study. Databases were searched until October 2016. The pooled effects of outcomes with heterogeneity were calculated with a random-effects model, heterogeneities were analysed by subgroup and meta-regression. As a result, twenty studies with 2106 participants were included in the meta-analysis. Total cholesterol and LDL-cholesterol levels were lower following low-fat diets compared with high-fat diets: weighted mean difference (WMD) was −7·05 mg/dl (−0·18 mmol/l; 95 % CI −11·30, −2·80; P=0·001) and −4·41 mg/dl (−0·11 mmol/l; 95 % CI −7·81, −1·00; P=0·011), respectively. Conversely, significant higher level of TAG (WMD: 11·68 mg/dl (0·13 mmol/l), 95 % CI 5·90, 17·45; P<0·001) and lower level of HDL-cholesterol (WMD: −2·57 mg/dl (−0·07 mmol/l); 95 % CI −3·85, −1·28; P<0·001) were found following low-fat diets compared with high-fat diets. In conclusion, dietary fat manipulation has a significant influence on blood lipid levels in people with overweight or obesity without metabolic disturbances.

In recent years, new functional roles of vitamin D beyond its traditional role in calcium homoeostasis and bone metabolism have emerged linking the fat-soluble vitamin to various non-communicable diseases. Vitamin D deficiency (25-hydroxyvitamin D (25(OH)D) < 25–30 nmol/l) and sub-optimal status (25(OH)D < 50–100 nmol/l) are increasingly associated with unfavourable metabolic phenotypes, including insulin resistance, type 2 diabetes and CVD; conditions also commonly linked with overweight and obesity. Early studies reported poor vitamin D status in the morbidly obese. More recently, it has been observed that a graded relationship between vitamin D status and BMI, or specifically adiposity, exists in the general population. A number of hypotheses have been proposed to explain the potential mechanisms whereby alterations in the vitamin D endocrine system occur in the obese state. Plausible explanations include sequestration in adipose tissue, volumetric dilution or negative feedback mechanisms from increased circulating 1,25-dihydroxyvitamin D3. Others hypothesise that heavier individuals may partake in less outdoor activity, may also cover-up and wear more clothing than leaner individuals, thus decreasing sun exposure and limiting endogenous production of cholecalciferol in the skin. Moreover, in some but not all studies, BMI and adiposity have been negatively associated with the change in vitamin D status following vitamin D supplementation. It therefore remains unclear if body size and/or adiposity should be taken into account when determining the dietary requirements for vitamin D. This review will evaluate the current evidence linking vitamin D status and supplementation to overweight and obesity, and discuss the implications for setting dietary requirements.