Researchers have found that women who follow strict exercise and diet regimens may harm their body's ability to form new bone, which can lead to osteoporosis later in life.
This means that the more women exercise, the more they need to eat to stay healthy.
The study was conducted by a team of researchers lead by Anne Loucks at the Ohio University.
As part of the study, researchers studied women by restricting the caloric intake of two groups of women with regular menstrual cycles and normal body fat over five days.
Participants exercised for nearly two hours each day. One group ranged in age from 18 to 23 years, and the other was aged 26 to 32.
Scientists know that bone formation continues in adulthood, as old bone is continually being replaced with new bone.
Researchers found that in both age groups, two bone formation markers were suppressed, suggesting that low energy availability impairs bone formation in adults as well as adolescents.
Although the reproductive system is much less dependent on energy availability in slightly older women after they stop growing, these women remain at risk for bone loss.
Low bone density puts women at higher risk for stress fractures and can lead to osteoporosis.
"Appetite is not a good indicator of how much female athletes should eat, and neither is a regular menstrual cycle," Loucks said.
"Thousands of women severely restrict their diet and practice rigorous exercise programs for fitness and weight control. Because some don't see obvious signs of undernutrition, such as a disrupted menstrual cycle, they may think they're eating enough. If their diet does not supply enough energy to fuel their exercise level, though, they may be harming themselves. They need to replenish those calories," Loucks added.
The findings of the study were presented at the Endocrine Society annual meeting in Toronto.