The heaviest coffee drinkers carried less body fat and more muscle than those who drank little or none, a large population study of middle-aged adults has found. They also had less of the fat that wraps around the internal organs.

What they did not show was a lighter frame for their height. On that standard measure of body size, the groups looked much the same.

That is the catch, and it is not the only one. The difference was not in how heavy people were, but in what their bodies were made of.

Coffee has long been tied in research to lower rates of type 2 diabetes and heart disease. How it might produce those differences has never been clear.

Same Weight, Different Body

A 2026 study asked participants about their health, diet, activity, medications, conditions and lifestyle habits, including how much coffee they drank. Intake ranged from none at all to several cups a day.

Participants fasted overnight and skipped their coffee before testing. Researchers then estimated fat and muscle, took blood and gave everyone a sugary drink to see how their bodies coped.

The team also tried to strip out the obvious explanations. The comparisons were adjusted for smoking, alcohol, physical activity and education, as well as for body size.

Some of the difference sat deep in the abdomen. Fat stored there, around the internal organs, is closely linked to problems including heart disease.

The muscle went the other way. Those drinking the most carried more of it, leaving two groups of much the same size with quite different body compositions.

Those who drank more also had lower levels of protein building blocks in the blood, known as branched-chain amino acids. When these stay high over time, research links them to a greater risk of type 2 diabetes.

Where the Catch Comes In

The results split by sex. Men showed more favourable blood sugar and insulin readings the more coffee they drank, while in women those links were fewer and weaker.

More coffee was not uniformly good news for men, either. Some of them had higher levels of cholesterol-carrying particles in the blood and lower readings for omega-3 fats.

Men who drank more also had higher total testosterone, while other measures of the same hormone moved slightly the other way. In women, the hormonal links were more limited.

That pattern is what interested the researchers most. The lead author described a 'distinct hormonal signature' that held up even after weight and lifestyle habits were taken into account.

The scientists behind the work are blunt about this: none of it proves coffee is responsible. The study looked at people at a single point in time, so it can show two things travelling together but not that one causes the other.

Leaner people may simply drink more coffee, rather than the coffee making anyone leaner. There is no way, from data like this, to tell which came first.

The findings did not show that coffee lowered those amino acids, either. Lower levels may just be part of a healthier metabolic picture that was already in place.

The team is now trying to work out whether coffee itself causes any of this. That work is being done in animals first, with human trials the longer-term aim.

Until then, the researchers say the findings are not firm enough to change what anyone is told to eat or drink. Far more evidence would be needed before advice shifted on the strength of them.

There is plenty the study did not record. Cup sizes, brewing methods and whether anyone added milk, sugar or flavourings were all left out of the picture.

So the leaner bodies are real, but the reason behind them is not settled. On this evidence, nobody should start drinking coffee expecting it to shift fat.

Read more