A new Finnish study has found that people who regularly drank more coffee tended to have a leaner body-composition profile, including lower total and visceral fat and greater skeletal muscle mass, even though their body mass index (BMI) was broadly similar to that of people drinking less coffee.
The research also identified notable differences in the way coffee consumption was associated with sex hormones. The strongest pattern appeared in men, where higher habitual coffee intake was associated with higher total testosterone and sex hormone-binding globulin (SHBG), but lower free testosterone and free androgen index.
The findings come from researchers at the University of Oulu and are based on data from 2,264 adults aged 46 who participated in the Northern Finland Birth Cohort 1966. The study was published on July 16, 2026, in the European Journal of Nutrition.
The results are potentially significant because they suggest that the relationship between coffee and metabolic health may involve more than caffeine’s immediate effects. At the same time, the researchers stress that the study cannot establish that drinking coffee causes lower body fat or changes hormone levels.
The BMI finding is more complicated than it first appears
One of the more interesting observations was the difference between BMI and actual body composition.
Participants with higher coffee consumption had lower body-fat percentage, lower absolute fat mass and less visceral fat, while skeletal muscle mass was higher. Yet BMI did not show the same difference between consumption groups.
That matters because BMI does not distinguish between fat and muscle. Two people can have the same BMI while having substantially different amounts of body fat and lean tissue.
The researchers therefore looked beyond BMI, using bioelectrical impedance analysis to estimate body composition. They found a dose-related pattern in which higher coffee consumption was associated with a leaner profile.
However, these measurements should not be interpreted as proof that coffee itself reduces body fat. Bioelectrical impedance provides an indirect estimate of body composition, and the observational design leaves open the possibility that other differences between participants contributed to the findings.
The study included mostly coffee drinkers
The final analysis consisted of 2,264 participants, including 2,194 coffee consumers and only 70 people who did not consume coffee. Participants were grouped according to habitual intake: 1–2 cups per day, 3–4 cups, and five or more cups.
Coffee intake was self-reported, and the researchers noted an important limitation: the questionnaire did not define the volume of a “cup.” Information about factors such as exact serving size, brewing method and bean type was also unavailable.
That makes it difficult to translate the findings directly into a recommendation such as “drink five cups a day.” The study was designed to examine associations between habitual consumption and biological markers, not to determine an optimal amount of coffee.
Men’s hormone profile showed the clearest association
The most pronounced hormonal differences emerged among men.
After adjusting for BMI, education, smoking, physical activity and alcohol consumption, each additional cup of coffee per day was associated with an increase of about 0.29 nmol/L in total testosterone. Coffee intake was also positively associated with bioavailable testosterone and SHBG.
At the same time, the study found lower free testosterone and a lower free androgen index among men with greater coffee consumption.
That combination is important. A rise in total testosterone does not necessarily mean that more testosterone is freely available for tissues. SHBG binds sex hormones in the bloodstream, so changes in SHBG can alter the relationship between total and free testosterone.
For that reason, the findings should not be simplified into the claim that “coffee boosts testosterone.” The researchers found an association with a broader hormonal pattern, rather than evidence that coffee directly increases men’s functional testosterone levels.
Women’s hormone associations were more limited
The hormonal picture was different among women.
Higher coffee consumption was associated with higher SHBG and lower free testosterone and free androgen index. However, the researchers did not find significant associations between coffee intake and total or bioavailable testosterone in women in the fully adjusted analysis.
The researchers also restricted the female hormonal analysis to women without a reported diagnosis of polycystic ovary syndrome and with relevant data available, reflecting the known influence of PCOS on androgen-related measures.
The sex-specific results suggest that coffee’s relationship with endocrine and metabolic markers may not be identical in men and women.
Metabolic markers also differed by coffee intake
The study found another consistent signal across both sexes: higher coffee intake was associated with lower circulating levels of branched-chain amino acids, or BCAAs.
These amino acids are essential nutrients, but chronically elevated circulating BCAA levels have been associated in previous research with insulin resistance and metabolic disease. The Finnish researchers therefore identified the finding as potentially relevant to the metabolic effects associated with habitual coffee consumption.
Among men, higher coffee intake was also associated with several measures suggesting a more favourable glucose-insulin profile, including lower fasting insulin and lower insulin responses during an oral glucose tolerance test.
The associations in women were generally weaker, although some relationships with measures of adiposity, inflammation and insulin sensitivity were observed.
Why the findings do not prove coffee is responsible
The biggest limitation is the study design.
Researchers analysed cross-sectional data, meaning coffee consumption and biological measurements were assessed within the same period. This allows researchers to identify relationships but cannot establish which factor came first.
For example, it is possible that habitual coffee drinkers differ from non-drinkers in ways that were not completely captured by the statistical adjustments. Diet, stress, sleep, other lifestyle habits and other unmeasured factors could potentially influence both coffee consumption and metabolic health.
The researchers adjusted their models for several important factors, including BMI, education, smoking, physical activity and alcohol consumption. Sensitivity analyses also produced broadly similar results after excluding people with extreme BMI values or those taking certain cardiovascular medications.
Even so, adjustment cannot eliminate every possible source of confounding.
The researchers also point out that testosterone varies naturally within individuals and that the study measured hormone levels at a single time point. The results therefore describe population-level associations rather than predictable hormonal changes in an individual coffee drinker.
Sources Used :
PubMed Central — Full-text version of the research paper. Read the full-text study
European Journal of Nutrition — Associations of habitual coffee intake with testosterone and cardiometabolic markers: the Northern Finland Birth Cohort 1966 study, published July 16, 2026. Read the full study on Springer Nature
PubMed — Bibliographic record for the study and author information. View the PubMed record
What comes next for coffee research
The Finnish findings add another piece to a much larger research question: why has coffee consumption repeatedly been associated with aspects of metabolic health?
Caffeine is one possible explanation, but coffee contains many other biologically active compounds. The new study’s authors say future longitudinal and intervention studies will be needed to determine whether coffee itself causes the observed changes and which compounds might be responsible.
For consumers, the practical takeaway is more modest than the headline might suggest. The study does not establish that increasing coffee intake will reduce visceral fat, improve testosterone levels or prevent diabetes.
What it does provide is evidence that habitual coffee consumption is associated with a measurable metabolic and hormonal signature—and that this signature appears to differ between men and women.
The next step is determining whether those associations survive controlled intervention studies. Until then, the research is best viewed as a clue about how coffee may interact with metabolism and hormones, rather than as a prescription to drink more of it.
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