Same BMI, less fat: coffee tied to leaner body composition

Clinical takeaway: Habitual coffee intake may track with lower body fat and higher muscle mass, differences that BMI and waist measurements do not capture. 

Coffee looks metabolically protective, but no one quite understands why. The association with lower rates of type 2 diabetes and cardiovascular disease has held across decades of cohort studies. The potential pathways run through fat accumulation and distribution, insulin processing, and the endocrine system, none of which are typically assessed at a routine visit. 

Weight, height, and waist size define bodily dimension, but don't offer insight into body composition or hormonal processes. A new analysis examined the metabolic implications of coffee consumption, including measuring body composition, circulating metabolites, insulin handling, and sex hormones in more than 2,000 middle-aged adults with unusually high coffee intake. 

Across intake groups, BMI and waist circumference were effectively identical, but body composition was not. Body fat averaged 27.1% among those drinking five or more cups a day compared with 30.4% among light consumers, fat mass ran about 2 kg (4.4 lbs) lower, and visceral fat area was lower as well. Skeletal muscle mass ran higher, averaging 32.5 kg in the heaviest consumers compared with 30.2 kg in the lightest. All four measures showed dose-related trends. 

In men, higher intake correlated with lower fasting insulin, lower insulin across the glucose tolerance test, and higher insulin sensitivity. Branched-chain amino acids, which run high years before type 2 diabetes declares itself, were inversely correlated with intake in both sexes. 

The hormonal pattern was the most clearly sex-specific finding: in men, each additional daily cup was associated with higher total testosterone and higher sex hormone-binding globulin (SHBG), the carrier protein that determines how much testosterone is available to tissue. Because SHBG rose, free testosterone and the free androgen index ran lower. In women, only the SHBG shift held. 

The findings come from a cross-sectional analysis of 2,264 adults in the Northern Finland Birth Cohort 1966, all examined at age 46. Coffee intake was self-reported by daily cup count, and participants fasted overnight and abstained from coffee before testing. Hormonal models adjusted for BMI, education, smoking, physical activity, and alcohol, and the associations held after adjustment. 

Cross-sectional design leaves direction unresolved, and leaner adults may simply drink more coffee. Heavy consumers also smoked more, and body composition was estimated by bioimpedance rather than imaging. 

Whether coffee causes any of this remains open, and the authors are pursuing it in animal models with human trials as the eventual goal. Caffeine is the presumed active compound, but decaffeinated coffee has produced similar acute testosterone responses, so the mechanism is not settled. 

"Coffee is consumed by millions of people every day, yet we still know surprisingly little about how it relates to our metabolism and hormones. What stood out in our findings was a distinct hormonal signature that didn't disappear even after we took into account BMI and lifestyle factors, with several of these associations differing between men and women," said Luca Verroest, a doctoral researcher at the University of Oulu who led the study. 

Source: Verroest L, et al. (2026 Jul 16) Eur J Nutr. Associations of habitual coffee intake with testosterone and cardiometabolic markers: the Northern Finland birth cohort 1966 study