Researchers in Finland, where coffee is less a drink than public infrastructure, examined 2,264 men and women, all aged 46.
They compared non-drinkers with people consuming one to two, three to four, or at least five cups a day. The bigger coffee drinkers had less total body fat, less visceral fat and more skeletal muscle, despite having roughly the same BMI.
Among men, the results became even more interesting. More coffee was linked with lower fasting insulin, less insulin resistance and better insulin sensitivity. Poor insulin sensitivity is closely linked with type 2 diabetes, while building and maintaining muscle may substantially reduce the risk. Total and bioavailable testosterone were also higher.
At this point, coffee had wandered out of the café and begun rearranging the supplement aisle.
The Testosterone Twist
The hormone result was not quite as simple as “drink coffee, become more man”.
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Men who drank more coffee had higher total testosterone and higher levels of sex hormone-binding globulin, or SHBG. But their calculated free testosterone was slightly lower.
That sounds contradictory, but testosterone does not simply float around the bloodstream waiting to grow a beard. Much of it travels attached to proteins. SHBG binds it tightly, so an increase in SHBG can raise the total amount being carried while reducing the fraction that remains completely unbound.
Bioavailable testosterone, which includes free testosterone plus hormone more loosely attached to another protein, was slightly higher.
So the men had more testosterone in some measurements and less in another. Biology, as usual, declined to provide a clean headline.
The researchers also found lower levels of circulating branched-chain amino acids in people who drank more coffee. That does not mean coffee was robbing their muscles of leucine. Chronically high BCAA levels in the blood can indicate that the body is not processing them properly and have been linked with insulin resistance and metabolic disease. Taken together, the coffee drinkers appeared leaner and more metabolically healthy.
Before Your Have Your 6th Coffee
The study did not prove that coffee caused any of this. It was a snapshot of people at one point in their lives, using information collected in 2012. Coffee intake was self-reported, a “cup” was never defined and researchers did not record the beans, caffeine content or what people added to the drink.
There were also only 70 non-coffee drinkers. More than 1,000 participants drank at least five cups a day, which tells you as much about Finland as it does about coffee.
Most importantly, the heavy-coffee groups contained more men. Men made up 35 per cent of the low-intake group but 55 per cent of the high-intake group. Since men usually carry more muscle and less body fat than women, that imbalance could explain some of the apparent advantage.
Coffee drinkers may also exercise more, eat differently or possess some other life habit the researchers could not completely account for.
It certainly does not show that five cups a day will strip belly fat, build muscle or fix low testosterone. Depending on what is in them, they may achieve precisely the opposite.
But if you already enjoy coffee and it does not wreck your sleep, there is no bad news here. Coffee remains cheap, legal, mildly performance-enhancing and one of the few pleasures left that researchers have not conclusively ruined.
Just don’t mistake the barista for your strength coach.
The study was published in the European Journal of Nutrition by researchers from the University of Oulu and collaborating institutions. Read the University of Oulu’s summary here.
