Why Men Are Always So Warm
It may be comforting to have a warm bed partner, but it comes at a cost.
Posted September 21, 2025 | Reviewed by Abigail Fagan
Many of my male students participate in some form of daily exercise routine. Every year, I warn them about the consequences of too much exercising, but they are young and feel immortal and usually choose to ignore my advice. Yet being a male—or more accurately, having lots of testosterone circulating through the body, whether you have lots of big muscles or not—complicates the impact of exercise and energy production on mitochondrial function and your body’s health.
Testosterone increases the energy expenditure from muscle mitochondria , leading to an increase in the number of mitochondria within each muscle and an increase in the production of ATP. Much of the energy used for the increased production of ATP is drawn from the body’s stored fat. So far, this all sounds OK.
The hormone -driven mechanisms that control the metabolism of fat for energy have significant consequences for males. Testosterone alters how males metabolize food and increases the amount of heat their muscles produce during normal respiration.
Testosterone, due to its effects on a specialized protein, called uncoupling protein or thermogenin (referring to its ability to produce heat), makes the normal food-to-energy conversion process in mitochondria become inefficient—that is, cells waste more energy as heat; this tends to make men feel warm. Lacking both comparable levels of testosterone and the same degree of muscle mass (typically), women tend to produce less body heat from their food; consequently, it is usually much harder for women to lose weight than it is for men.
The male body, particularly all of those muscles that contain lots of mitochondria, is capable of wasting a considerable number of consumed calories as body heat. This explains why the principal method of dieting for many of my male students is to eat anything they want and then exercise away the calories. Or they could do nothing at all. Some men, to the chagrin of many women, seem to lose weight by simply sitting still. In contrast, women, who lack the mitochondrial uncoupling actions of testosterone, are often forced to lose weight the old-fashioned way: by not consuming as many calories.
Yet for males, wasting calories in order to produce heat has some negative long-term consequences. First of all, because of their generally increased size and total muscle mass, males typically need to consume more calories per day than do females; consequently, males generate more harmful reactive oxygen- free radicals —ROS. These ROS are quite harmful to the body and negatively affect men’s health and reduce their longevity, as compared to women. This situation can be made worse by purposely increasing muscle mass and consuming additional calories to support the additional activity of these muscles.
Numerous studies have shown that bodybuilders have a shortened life span as compared to the rest of the male population. The studies often claim that the cause of their increased mortality is the use of human growth hormone, anabolic-androgenic steroids, and excessive use of bodybuilding supplements. Although these factors may contribute, they do not explain the entire problem. It's not just human males who have reduced life spans due to eating and breathing. Males of all species, including spiders, flies, the birds and the bees, on average, never live as long as the females of their species.
This is true even for species with a very short life span, such as a fly. Male flies of one species have an average maximum life span of five days; the females of the same species have an average maximum life span of seven days.
In contrast to men, women waste less energy as heat, need to consume fewer calories every day in order to survive, and produce fewer ROS; all of which benefit their overall brain health and longevity. But if ROS are so harmful, why does your body produce them?
Because you have no choice. If you have stopped making ROS, you are probably dead.
Facebook image: NDAB Creativity /Shutterstock
Wenk GL, (2021) Y our Brain on Exercise . Oxford University Press.
James M Smoliga JM, et al., (2023) Premature Death in Bodybuilders: What Do We Know? Sports Med. 53(5):933–948. doi: 10.1007/s40279-022-01801-0, PMCID: PMC9885939, PMID: 36715876
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Gary L. Wenk, Ph.D. , is a professor of psychology, neuroscience, molecular virology, immunology and medical genetics at the Ohio State University.
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This article is part of the Bringwise Psychology Journal — daily insights on human behavior, mental health, and personal growth.