The way fat stores are metabolised during exercise is different in males and females, according to a US study, which shows the need for more research into how exercise impacts the female body.

Published in the journal Nature Metabolism, the research was undertaken by the Molecular Transducers of Physical Activity Consortium, a collaboration of more than 100 scientists across a number of universities, studying the molecular changes which occur during and after exercise to advance the understanding of how physical activity improves and preserves health.

While exercise improves the health of fat stores in both sexes, making them more metabolically active, scientists discovered vast differences in the way fat tissues in males and females responded to running on a treadmill over an eight week period.

While males burned fat for energy, females were more likely to preserve and 'recycle' their fat mass.

Although females burned fat at the start of the trial, by the end of eight weeks their fat stores had reverted to how they had been at the start. However, they did not gain fat in the way their sedentary counterparts did.

"We saw both sexes mobilise their metabolism to get the energy they need," said first author Gina Many. "But they get their energy in different ways. Females do so without drawing so much from their fat stores, likely because these are critical to reproductive health."

While too much body fat can cause disease in some people, depending on how and where their body stores it (with this differing according to body type and genetics), having body fat is also important for health, as it controls parts of the endocrine system, among others.

In recent decades, scientists have learned that fat isn't just unwelcome weight, but a major organ that runs through the body. Like the skin, it secretes hormones and other compounds that play an important role in our health.

Ovulation and menstruation typically stops if women's body fat drops below 18 per cent, with 22 per cent currently thought to be the optimum level.

"These findings help set the landscape to understand disease risk and establish a basis for more personalised and targeted health interventions," said Many.

The results also highlight the need for health studies to include males and females, as traditionally research has been heavily skewed towards males. Contributing author, Christopher Newgard, said: "The differences between the sexes are much more vast than I would have anticipated. This is changing the way I'm approaching other studies, including one on insulin resistance in males and females. These findings provide a road map for those experiments."

The scientists found that no tissue studied went unchanged during exercise, with 35,000 different molecules affected from the 18 tissue types studied, including blood.

The extensive benefits of exercise include enhanced liver function, stronger heart muscle, enriched immunity and reduced inflammation in the lungs and gut. Mitochondria – the energy producers in cells – also becomes healthier after exercise. The study was funded by the National Institutes of Health Common Fund in the US.

The results of the research, When working out, males are programmed to burn more fat, while females recycle it..., have prompted a further study on a sample of 1,500 people.