Body Composition Statistics: Body Fat & Lean Mass Norms

In US men, the body-fat percentage that matches a BMI of 25 ranges from 22.6% to 28.0%, and a BMI of 30 from 27.5% to 32.3%, depending on age and ethnicity

DXA measurements of 6,544 men in NHANES 1999-2004. The oldest age group had the highest body fat at a given BMI and non-Hispanic Black men the lowest.

In US women, the body-fat percentage that matches a BMI of 25 ranges from 35.0% to 40.2%, and a BMI of 30 from 39.9% to 44.1%

DXA measurements of 6,362 women in the same survey. Women carry more fat than men at every BMI.

Body-fat percentage could be predicted from BMI, sex, age and ethnicity with a standard error of 2.8-5.4 percentage points

1,626 white, African American and Asian adults measured with reference methods at three universities; the equations were used to propose healthy body-fat ranges linked to BMI limits.

A BMI of 30 or more identified obesity in 19.1% of men and 24.7% of women, while body-fat measurement identified it in 43.9% and 52.3%

13,601 adults aged 20-79 in NHANES III, with obesity defined as body fat above 25% in men and 35% in women (estimated by bioimpedance).

A BMI cut-off of 30 caught only 36% of men and 49% of women with excess body fat, though it rarely flagged people who were not over-fat (specificity 95% and 99%)

BMI misses more than half of people with excess fat, especially at BMI 25-29.9, in men and in older adults; it does not mainly misclassify muscular people.

Men carried 33.0 kg of skeletal muscle on average against 21.0 kg in women, 38.4% versus 30.6% of body mass

Whole-body MRI in 468 adults aged 18-88. The sex gap was larger in the upper body (40%) than the lower body (33%).

Muscle as a share of body mass starts falling in the third decade, but a noticeable fall in absolute muscle mass does not appear until the end of the fifth decade

The later decline came mainly from lower-body muscle.

The height-adjusted FFMI of 74 male athletes who said they had never used steroids extended up to 25.0; 20 Mr. America winners from 1939-1959 averaged an estimated 25.4

Many of the 83 steroid users exceeded 25.0 and some exceeded 30. Non-use was self-reported and the authors called the findings preliminary, so 25 is a screening line, not a proven natural ceiling.

Bioimpedance equations built on a multicomponent reference predicted fat-free mass with errors of 3.9 kg in men and 2.9 kg in women

1,829 people aged 12-94 from five centres. The equations overpredicted fat-free mass slightly in white participants and underpredicted it by 2.1 kg in Black men.

Jackson-Pollock skinfold equations predicted body density with correlations above 0.90 and a standard error of about 0.0077 g/ml

Developed on 308 men aged 18-61 and cross-validated on 95 more. With the Siri equation, 0.0077 g/ml is about 3.4 percentage points of body fat (our conversion).

Most studies comparing DXA body composition with the four-compartment reference model found significant differences

Review of pencil-beam to narrow fan-beam DXA scanners. How much newer technology has improved accuracy remained unclear.

Waist-to-height ratio improved detection of cardiometabolic risk by 4-5% over BMI, against 3% for waist circumference

Meta-analysis of 31 studies with more than 300,000 adults across ethnic groups, covering hypertension, type 2 diabetes, dyslipidaemia, metabolic syndrome and cardiovascular outcomes.

Lifestyle interventions that produce weight loss generally mobilize visceral fat preferentially

Review of visceral obesity. Measuring waist circumference alongside BMI helps identify overweight patients at high cardiometabolic risk.

Twin studies put the heritability of BMI at 0.47-0.90 (median 0.75); family studies at 0.24-0.81 (median 0.46)

Systematic review of 88 twin estimates (140,525 twins) and 27 family estimates. Study design explained nearly half the spread between twin studies.

BMI heritability was 0.07 higher in children than in adults, and fell slightly with age through adulthood

Meta-regression of the same twin studies; genes appear to matter more for body size in childhood.

In lean, resistance-trained athletes in a calorie deficit, body fat fell 0.5-6.6% in all 13 study groups and fat-free mass fell 0.3-2.7 kg in nine of them

Systematic review of six studies. Groups that kept their fat-free mass were mostly fatter, in a smaller deficit or on a new training stimulus; the authors recommend 2.3-3.1 g of protein per kg of fat-free mass.