Endurance inhibitor: Caloric cuts compromise athletic performance, study flags

22 Jul 2024 --- The widespread practice of caloric restriction among athletes to be lean could be harmful, according to recent research findings. Following extensive evaluation of the method, researchers at the University of Copenhagen, Denmark, conclude that it can damage athletic performance and individual health, particularly for female endurance athletes.

“Cautioning women on their vulnerability to insufficient energy intake is challenging because the adverse health consequences of low energy availability (LEA) have been known for decades, yet many women still engage in behaviors that lead to LEA,” Jan Sommer Jeppesen, a Ph.D. student at the University of Copenhagen and lead author of the study, tells Nutrition Insight.

“A large proportion of women with insufficient energy intake experience it unintentionally; they cannot compensate for a large exercise-induced energy expenditure and, as a result, may not realize they aren’t eating enough. Their metabolism could be suppressed, causing body weight to remain stable despite insufficient intake.”

The widespread practice of reducing dietary intake in the run-up to competition is mainly practiced among endurance sports athletes, particularly those who run, swim, cycle or row.

Signs of reduced performance
The researchers recruited twelve female triathletes with normal energy intake to participate in the study, which has been published in Redox Biology. In one module of the trial, the athletes were given enough calories for 14 days, after which their performance was tested. In another 14–day module, the same athletes consumed only about 50% of their energy needs while sticking to their normal intensive training schedule.

In the latter experiment, the athletes lost an average of roughly 4% of their body weight, about half of which was muscle mass and experienced a loss in performance.

“It is particularly problematic among female endurance athletes. Many athletes focus heavily on weight in their respective sports. Consequently, they tend to go into short-term but intense periods of weight loss with the expectation of performing better,” says Ylva Hellsten, professor in the Department of Nutrition, exercise and Sports at the University of Copenhagen.

“Many coaches continue to pressure athletes to lose weight. For many years, it has been a part of the culture in the sports world and remains so. We need to shed light on the phenomenon and ask critically: ‘What are we actually doing to our athletes both physically and psychologically?’”Sufficient energy availability facilitates a better recovery after sport.

After 14 days of insufficient food intake, they reduced their performance by 7.7% in a 20–minute bike trial. During a more intense short-term test, their performance slid by 18%. The phenomenon is associated with many harmful health conditions, including missed periods, compromised bone health and changes in metabolism.

Jeppesen notes: “For athletes with very high exercise-induced energy expenditure, there should be a greater focus on ensuring they compensate for this expenditure. Coaches have a significant responsibility in this regard. They should be able to identify athletes who might be at risk of LEA and take proactive steps to address it.”

“We cannot place all the responsibility on the athletes alone; therefore, coaches should learn more about LEA and actively monitor their athletes’ energy intake and expenditure. By doing so, they can help prevent the adverse effects associated with insufficient energy intake, particularly in female athletes.”

Athletes and coaches should carefully monitor this and make sure not to make any drastic changes. An easy method is to measure body weight and ensure no large fluctuations within weeks. However, as a long-term insufficient energy intake could suppress metabolism, maintaining body weight doesn’t always mean that daily energy intake is sufficient.

“We currently do not have any perfect markers of sufficient energy intake; many research groups are currently looking for good biomarkers of LEA. We show that cortisol might be a good marker,” says Jeppesen.

The study is supported by the Danish Ministry of Culture, the Frimodt-Heinike Foundation, the Novo Nordisk Foundation and Team Denmark, an elite sports organization.

Diminished immunity
In addition to sports performance, the researchers examined the effects on athletes’ immune function and observed that insufficient energy intake increased systemic stress. The athletes experienced a significant increase in cortisol and anxiety in the immune cells.

“This suggests that there is a quite severe impact on several aspects of the immune system if one doesn’t eat enough. This may potentially contribute to athletes being more exposed to illness,” says Jeppesen.

According to the researchers, studies have shown that ensuring sufficient energy availability can avoid health complications and overtraining. This constitutes the healthiest approach to providing adequate energy intake.Energy intake negatively affects women’s estrogen levels and physiology, making them more vulnerable to caloric restriction.

“If athletes need to lose weight, I suggest inducing a smaller calorie deficit (maybe 5–10%) and ensuring that the weight reduction is slow and steady. This approach would likely reduce the stress on the body (as we have shown is high when engaging in LEA) and help maintain performance,” Jeppesen explains.

“In general, there should be less focus on body weight, and athletes would often benefit from placing a larger emphasis on the quality of training rather than on body weight.”

The researchers maintain that the focus shouldn’t solely be on keeping an athlete’s weight low but on compensating for their energy expenditure. This is challenging, as many factors influence energy expenditure. If an athlete has been in a state of sufficient energy intake for a while, body weight can be a good indicator of the balance between energy intake and expenditure. Body weight can be influenced by other factors, such as the menstrual cycle.

“Based on our study, it is important to have a sufficient energy intake, as an insufficient intake clearly affects several aspects of athletic performance and health. As an example, we have recently shown that muscle protein synthesis is markedly reduced when LEA is introduced, and this could affect recovery,” says Jeppesen.

“Continuous sufficient energy availability will allow for ideal recovery and response to exercise training, thereby securing consistency in training, which is a key factor for improving exercise performance.”

Consistent degraded performance
After fourteen days of LEA, the athletes underwent a three-day refeeding period as part of the trial, during which they were provided plenty to eat.

“We had expected that the three days of enough food would restore their performance and maybe even improve it but there was absolutely no effect. Their performance was just as degraded as prior to the three days. This tells us that the negative effects cannot be reversed by quickly replenishing energy stores, which is a strategy used by many athletes,” says Jeppesen.

The research also shows that men are more resilient to insufficient energy intake. This gender difference is partly because low energy availability causes a woman’s estrogen levels to drop significantly. Estrogen protects the circulatory system, muscles and bones. Decreases in these levels have serious effects on a woman’s physiology and can be lifelong.

“Based on the rather limited research in this area, it seems that men are able to tolerate reduced energy intake before it affects them negatively. This indicates that women in particular are a vulnerable population in this respect,” Jeppesen concludes.

Meanwhile, ahead of the Olympic Games Paris 2024, ADM highlights its plant-based, pre-, pro- and postbiotic innovations for active nutrition. https://www.nutritioninsight.com/news/adm-leverages-active-nutrition-biotics-formulas-for-olympics-and-sports-season.html

By Inga de Jong

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