First-borns have a higher metabolic rate and carry a higher metabolic risk in young women attending a weight loss clinic.

BACKGROUND: Birth order has been associated with variability in early life growth and subsequent obesity risk, but the consequent metabolic risks have not been assessed. OBJECTIVE: To quantify the metabolic risk in young adulthood of being first-born relative to those born second or subsequently. METHODS: Body composition, resting metabolic rate and metabolic risk were assessed in 383 women, aged 18-35 years, from a clinical setting in southern Italy. RESULTS: First-borns had increased body mass index, adiposity and metabolic risk (p<0.05) and increased resting metabolic rate adjusted for fat-free mass (p<0.05) in the Italian women. CONCLUSION: First-born status is associated with significantly elevated metabolic risk in a clinical population of overweight and obese young women attending a weight loss clinic. If these findings are confirmed in other studies, they may suggest that the prevalence of the metabolic syndrome worldwide may increase as a function of the trend to smaller family size.