Women who exercise and limit their food intake could be harming their health, according to a study from the University of Otago.
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The university surveyed more than 109 female recreational athletes and found almost half developed a state of low energy availability.
The study suggested that for every hour a woman exercised each week, the risk of developing low energy increased significantly.
Women surveyed had to be non-elite athletes who did at least 150 minutes of moderate intensity physical activity per week, or shorter periods of more intense exercise.
Lead author Dr Katherine Black said if women did not get enough energy intake, the body acted to conserve energy through hormonal adaptations, which could end up harming reproductive abilities or bone health.
"We see changes to bone marrow density, so we get weaker bones.
"Unfortunately once we start losing that bone mass it's very, very difficult to actually regain that bone mass."
She said a low-energy intake could also affect mood and cause nutrient deficiences, such as a low iron count.
Research suggested some female recreational exercisers tried to cut back on meals, or certain food groups such as gluten, without a medical condition, she said.
"You may start skipping meals, and then we see a large drop in energy intake.
"Although you may see initial weight loss, in the long term it's not actually going to be beneficial to you."
It was important for women to get enough protein and carbohydrates if exercising, she said.
"If you're hungry you should have something to eat, so long as you're having a balanced and varied diet."
She said if women increased their energy intake, they could increase their energy output while exercising, which would counter any significant weight gain.
Dr Black said it was possible women were more likely than men to cut back on meals, due to societal pressure to stay slim.
The study also suggested links between athletes at risk of low energy availability and the number of training days taken off due to injury.
The findings were published in the International Journal of Sport Nutrition and Exercise Metabolism.
