Same BMI, different blood work. The study, published July 16 in the European Journal of Nutrition, compared body composition and metabolic markers across coffee intake levels in a Finnish birth cohort. People who drank more coffee carried less visceral fat and more skeletal muscle than people at the same BMI who drank less. BMI alone would have called them identical.
The glucose and insulin numbers moved together. Higher coffee intake tracked with a more favorable glucose and insulin profile and with lower branched-chain amino acids, a marker that rises with insulin resistance. Chronically elevated branched-chain amino acid levels have separately been linked to higher type 2 diabetes risk.
Testosterone and SHBG went up too, and the pattern split by sex. Coffee drinkers showed higher total and bioavailable testosterone and higher sex hormone-binding globulin. Lead author Luca Verroest described a hormonal signature that held after adjusting for BMI and lifestyle, with several associations differing between men and women.
A cohort study like this one shows association, not mechanism. People who drink more coffee may differ from people who drink less in ways the researchers could not fully measure, exercise habits, sleep, income, what else is in their diet. The paper adjusted for the usual suspects and the pattern held, but that is not the same as a trial that gives one group coffee and another a placebo.
None of this tells you what your own testosterone, glucose, or insulin numbers are doing right now. A cohort average moving in one direction says nothing about where you personally sit on any of those three markers.
Insulin resistance can show up in your blood work well before glucose does. See why fasting insulin belongs on your panel for the marker most standard panels skip.