Insulin sensitivity is increased and fat oxidation after a high-fat meal is reduced in normal-weight healthy men with strong familial predisposition to overweight.

OBJECTIVE

To evaluate whether postprandial abnormalities of energy expenditure and/or lipid oxidation are present in healthy, normal-weight subjects with a strong family history of obesity and thus at high risk to become obese.

DESIGN

Case-control study.

SUBJECTS

A total of 16 young healthy men participated in the study. Eight subjects had both parents overweight (father's and mother's body mass index (BMI) >25 kg/m(2)) and eight had both parents with normal body weight (father's and mother's BMI<25 kg/m(2), respectively). The group of subjects with overweight parents was similar to that with normal-weight parents (control group) in terms of BMI (23.7+/-1.7 vs 22.7+/-1.1 kg/m(2)) (M+/-s.d.) and fat-free body mass (FFM) (60.5+/-4.9 vs 58.4+/-2.0 kg), but was slightly older than the control group (25.4+/-3.3 vs 22.7+/-2.4 y; P<0.05).

MEASUREMENTS

Energy expenditure (EE) was measured by indirect calorimetry, and blood samples were taken for the evaluation of metabolic variables in the fasting state and every hour for 8 h after a standard fat-rich meal (protein 15%, carbohydrate 34%, fat 51%, 4090 kJ).

RESULTS

Fasting plasma glucose, cholesterol, HDL-cholesterol, triglyceride, free fatty acid (FFA) and leptin concentrations were similar in both groups of participants, but subjects with overweight parents has significantly lower plasma insulin concentrations (5.11+/-0.51 vs 7.07+/-1.56 microU/ml; P<0.007) and HOMA index of insulin resistance (1.1+/-0.1 vs 1.6+/-0.4; P<0.01). Postprandial plasma glucose, triglyceride, FFA and leptin concentrations were similar in the two groups, whereas insulin levels were significantly lower in the group with both parents overweight at 3, 5, 6, 7 and 8 h. Fasting and postprandial EE, and fasting lipid and carbohydrate oxidation were similar in both groups. On the contrary, postprandial carbohydrate oxidation (incremental area under curve) was significantly higher (196.25+/-94.75 vs 75.88+/-74.72 mg/kg FFM x 8 h; P<0.007) and that of lipid oxidation lower (90.93+/-80.32 vs 163.68+/-108.22 mg/kg FFM x 8 h; P<0.05) in the group of subjects with overweight parents.

CONCLUSION

Normal-weight subjects with a strong family history of obesity present a reduced lipid oxidation in the postprandial period and a metabolic profile characterized by low plasma insulin levels and the HOMA index, which is compatible with increased insulin sensitivity. These metabolic characteristics may be considered as early predictors of weight gain and are probably genetically determined.