The mean percentage body fat is 28.1% in men and 40.0% in women, according to a new study published in the American Journal of Clinical Nutrition.

A nationally representative sample of over 13,000 U.S. adults was taken from the National Health and Nutrition Examination Survey. Over a 6 year period (1999-2004), researchers collected total body fat and fat-free mass measurements using dual-energy X-ray absorptiometry. Percentage body fat was calculated using both measures.

In men, the average height was 5 feet, 8 inches with a weight of 192 pounds and a Body Mass Index (BMI) of 27.9. In women, the average height was 5 feet, 3 inches, with a weight of 164 pounds and a BMI of 28.2.

Due to its ease of calculation, BMI numbers are widely used to gauge healthy body weight. However, this measure can be misleading as it only takes into consideration height relative to weight; it does not measure the “quality” of a person’s weight.

BMI may overestimate body fat on those with more lean body mass (e.g. athletes) while underestimating body fat on those with less lean body mass (e.g. the elderly). For example, in two individuals with the same BMI, one could have a much higher percentage of body fat than the other.

In this study, researchers wanted to better understand the percent body fat, total body fat and fat-free mass among U.S. adults. In addition, they wanted to assess differences by sex, age, race-ethnicity and BMI.

Women had an average percent body fat 12 points higher than that of men, and this persisted after adjusting for age and race-ethnicity. In women, both non-Hispanic blacks and Mexican Americans had a higher percentage body fat than non-Hispanic whites and women of other races. Percent body fat and total body fat increased with age. But, in women, this decreased after age 55 and in men this measure decreased after age 65.

Women had on average about 11 pounds more total body fat than that of men and this persisted after adjusting for age and race-ethnicity. Non-Hispanic white men and non-Hispanic black women had the highest average total body fat than other races. Total body fat was highest in adults age 40-50 and 60-79 years.

Men had on average 40 pounds more fat-free mass than that of women and this persisted after adjusting for age and race-ethnicity (137 pounds vs. 97 pounds, respectively). The differences widened as BMI increased. In both men and women, fat-free mass was the highest in the 40-59 age group and in non-Hispanic blacks.

The Bottom Line

Given that this study used data from over four years ago, adiposity measurements among adults have probably declined further.

In a recent study published in the American Journal of Clinical Nutrition, the authors surmised that the increase in obesity over the past 30+ years was not related to lack of exercise but to excess caloric intake. To reverse this trend, they estimated that energy intake needs to be reduced by 500 calories a day in adults and by 350 calories a day in children.

Given that extra body fat is associated with increased risk for cardiovascular disease and type II diabetes, making the necessary dietary changes seems prudent