Gender differences in changes in subcutaneous and intra-abdominal fat during weight reduction: an ultrasound study

In weight-reducing programs, men usually display greater improvement in metabolic risk factors than women. This gender difference may be related to enhanced weight and fat loss due to a greater energy deficit in men. To clarify the relationship between changes in metabolic profile, body fat composition, and weight loss, both sexes were studied under a regimen in which similar amounts of weight were lost.

A cross-sectional study using anthropometric (body mass index and waist-to-hip ratio), impedance (bioelectrical impedance analysis) and ultrasound measurement methods (thickness of subcutaneous fat layers, intra-abdominal sagittal diameter) were conducted. The metabolic risk profile was determined by measuring lipids, lipoproteins, and blood pressure. The weight loss program lasted 15 weeks: 3 weeks under controlled conditions in the hospital and 12 weeks on an ambulatory basis. Patients were instructed to follow a mixed diet. Calorie intake was restricted to 1500 kcal/day for the men and 1200 kcal/day for the women. Thirty-two subjects with obesity (16 men and 16 women), with a mean body mass index of 35 kg/m2--matched with regard to age, height, and body weight--took part in the study.

As expected, weight loss was similar for both sexes (-13.4 kg vs. -12.8 kg). Also, body fat mass changed to the same extent in absolute and relative terms. The waist-to-hip ratio was identical before and after treatment in both sexes. The men lost more visceral fat than the women. This result is based on changes in intra-abdominal diameter as well as abdominal subcutaneous fat in relation to waist circumference. Changes in abdominal diameter were paralleled by reductions in triglycerides and increases in high-density lipoprotein-cholesterol. Subcutaneous fat loss was more pronounced in women than in men.

Where absolute and relative reductions in body weight and body fat are similar, men mobilize more intra-abdominal fat than women, whereas women lose more subcutaneous fat. The greater reduction in intra-abdominal fat seen in men is accompanied by a more pronounced improvement in the metabolic risk profile. Therefore, greater improvement of risk factors in men is not only related to a greater negative energy balance, as shown in most studies, but is also sex-specific.