Widespread practice among athletes harms both performance and health, study finds

Whether they’re being selected to swim, row or run in the Olympics or preparing to compete in the Tour de France, getting to the “right” weight has been a priority for many elite athletes for decades. That might mean looking lean and athletic in a swimsuit or bathing suit, or qualifying for a certain weight class. But there’s also a belief that losing weight improves performance.

It is therefore a common phenomenon among athletes – particularly in endurance sports such as running, swimming, cycling and rowing – to reduce their food intake before competition.

“This is particularly problematic among female endurance athletes. Many athletes place a high value on weight in their respective sports. As a result, they tend to engage in short-term but intense weight loss periods in the hope of achieving better performance,” says Professor Ylva Hellsten from the Department of Nutrition, Exercise and Sport at the University of Copenhagen.

She and doctoral student Jan Sommer Jeppesen are two of the researchers behind a new study on the effects of low energy availability in female athletes. The article is published in the journal Redox biology.

“We know that not eating enough is associated with many health risks, including missed periods, compromised bone health and changes in metabolism. But there’s still a lot we don’t know, so we took a closer look at some of the possible consequences,” said Jeppesen, lead author of the study.

Reduced cycling performance

For the study, the researchers recruited twelve female triathletes, all of whom had normal energy intake. During one portion of the trial, the athletes were given enough calories for 14 days, after which their performance was tested. The same athletes also underwent a 14-day period in which they consumed only about 50 percent of their energy needs while maintaining their normal intensive training schedule.

During the period when they were not getting enough calories, the athletes lost an average of about 4% of their body weight, about half of which was muscle mass. They also experienced a decline in performance:

“The fourteen days of undereating reduced their performance by 7.7% in a 20-minute cycling time trial, which is quite significant. And in a more intense short-duration test, their performance dropped by 18%. So there’s no doubt that this practice significantly impairs an athlete’s performance, even over shorter periods of time,” Jeppesen says.

Weaker immune system

In addition to athletic performance, the researchers looked at the effects on athletes’ immune function.

“In particular, we observed that insufficient energy intake was associated with increased systemic stress. The athletes had a large increase in the stress hormone cortisol and significantly increased stress levels in immune cells. This suggests that not eating enough has a pretty serious impact on several aspects of the immune system. This could potentially contribute to athletes being more susceptible to disease,” Jeppesen says.

The researchers hope the study’s results will help raise awareness of the phenomenon.

“Many coaches continue to pressure athletes to lose weight. This has been part of the culture of the sports world for many years and remains the case. We need to shed light on this phenomenon and ask ourselves a critical question: What are we really doing to our athletes, both physically and psychologically?” says Hellsten.

Denmark team to use results

Team Denmark, the Danish elite sports organisation, welcomes the new research results with open arms.

“This book addresses a very important topic and challenges the idea that lighter is better. This theory and culture is still prevalent in many sports. I meet many athletes who reduce their weight in the weeks leading up to a competition, but without understanding the consequences of this weight loss,” says Majke Jørgensen, sports nutritionist and manager of the Danish national team.

She sees the results as useful knowledge that can support a message the Denmark team has been trying to promote:

“My experience is that elite athletes and coaches are curious, but need research to support any criticism of the phenomenon. Here, the fact that the test subjects are real athletes is a major asset, as the results can be transferred to the athletes and coaches that the Danish team supports.

“We will use these findings to support what we are already trying to communicate, both when we sit down with athletes one-on-one, as well as in workshops and presentations in these types of settings,” says Jørgensen.

Three days of refeeding is useless

After fourteen days of low energy availability (LEA), the athletes underwent a three-day “refeeding” period as part of the trial, during which they were given a lot of food.

“We expected that these three days of adequate food would restore or even improve their performance, but it had no effect. Their performance was just as degraded as before these three days. This tells us that the negative effects cannot be reversed by rapidly replenishing energy stores, a strategy used by many athletes,” says Jeppesen.

Women more vulnerable than men

According to research, men tend to be more resilient to insufficient energy intake.

“From the relatively limited research in this area, it appears that men are able to tolerate a reduction in energy intake before it negatively affects them. This indicates that women in particular are a vulnerable population in this regard,” says Jeppesen.

The gender difference is partly due to the fact that low energy availability can cause estrogen levels to drop drastically in women. Since estrogen protects the circulatory system, muscles and bones, etc., estrogen loss has dramatic effects on women’s physiology.

Hellsten points out that the harmful effects of insufficient nutrition over long periods of time, especially in women, can therefore also last a lifetime.