Summary: Female athletes who consumed only half of their caloric needs for 14 days experienced significant declines in performance and muscle mass. This low energy availability also weakened their immune systems.
The harmful effects cannot be reversed by short-term refeeding, highlighting the risks of weight loss practices in sport. The findings highlight the need for awareness and better support for athletes.
Highlights:
- Performance drop: Low caloric intake led to a 7.7% decrease in cycling performance over 20 minutes.
- Muscle loss: The athletes lost an average of 4% of their body weight, half of which was muscle.
- Immune impact: Increased levels of stress hormones and immune cell stress due to low caloric intake.
Source: University of Copenhagen
Whether it’s swimming, rowing, or running 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. It 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 premium on their weight in their respective sport. As a result, they tend to lose weight in short but intense periods in the hope of improving their 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 14 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-term test, their performance dropped by 18%. So there’s no doubt that this practice significantly impairs an athlete’s performance, even over shorter periods,” 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 quite serious consequences for 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 program 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:
“In my experience, elite athletes and coaches are curious, but need research to back up their criticism of the phenomenon. The fact that the test subjects are real athletes is a major plus, 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 nutrition 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 their energy intake before it has negative consequences for 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.
About this research on diet and exercise
Author: Ylva Hellsten
Source: University of Copenhagen
Contact: Ylva Hellsten – University of Copenhagen
Picture: Image credited to Neuroscience News
Original research: Free access.
“Low energy availability increases reactive oxygen species formation by immune cells and impairs physical performance in female endurance athletes” by Ylva Hellsten et al. Redox biology
Abstract
Low energy availability increases reactive oxygen species formation by immune cells and impairs physical performance in female endurance athletes
Introduction
The effects of low energy availability (LEA) on the immune system are poorly understood. This study examined the effects of 14 days of LEA on immune cell redox balance and inflammation at rest and in response to acute exercise, as well as on physical performance in female athletes.
Methods
Twelve female endurance athletes (age: 26.8 ± 3.4 years, maximal oxygen consumption (𝑉˙O2max): 55.2 ± 5.1 mL × min−1 × kg−1) were included in a single-blind, randomized crossover study. They were assigned to start with 14 days of an optimal energy availability diet (OEA, 52 ± 2 kcal × kg lean body mass (FFM)−1 × day−1) or LEA diet (22 ± 2 kcal × kg FFM−1 × day−1), followed by 3 days of feeding (OEA) with training volume maintained. Peripheral blood mononuclear cells (PBMCs) were isolated and plasma obtained at rest before and after each diet period. PBMCs were used for analysis of mitochondrial respiration and H2O2 emission and specific proteins. Exercise performance was assessed on cycle by a 20-min timed trial and time to exhaustion at an intensity corresponding to ∼110% 𝑉˙O2max).
Results
Acute physical exercise increased H2 concentration in peripheral blood mononuclear cells (PBMCs) by 94% (P = 0.003) and systemic cortisol concentration by 22% (P = 0.013). Acute physical exercise increased H2 concentration in peripheral blood mononuclear cells (PBMCs) by 94% (P = 0.003) and systemic cortisol concentration by 22% (P = 0.013). Acute physical exercise increased H2 concentration in peripheral blood mononuclear cells (P < 0.05).2O2 Plasma PBMC concentrations were reduced (P < 0.001) after OEA and LEA, but to a greater extent after LEA. LEA also reduced white blood cell mobilization during acute exercise. After LEA, performance was reduced in both exercise tests (P < 0.001), and reduced performance in timed trials remained after the 3 days of refueling (P < 0.001).
Conclusion
14 days of LEA exercise in female athletes increased cortisol levels and had a pronounced effect on the immune system, including increased ROS production capacity, altered plasma inflammatory proteome, and decreased exercise-induced leukocyte mobilization. In addition, LEA exercise resulted in sustained impairment of physical performance.