While RED-S is complex, it comes down to a simple energy imbalance, said Pippa Woolven, former Commonwealth Games athlete and founder of Project RED-S, the athlete-led initiative dedicated to raising awareness and improving education about the condition.
RED-S happens when athletes do not eat enough to match the energy they burn through exercise and basic bodily functions. This energy shortfall disrupts key systems in the body. The consequences can be serious: fatigue, weaker bones, slower recovery, more frequent illness and injuries and reduced performance.
Drawing on her personal experience, Pippa launched Project RED-S in 2021, collaborating with healthcare professionals and athlete advocates to promote education and sustainable performance.
“A lot of the symptoms—like injuries, illnesses and fatigue—are so normalized in sports and exercise settings, that without even knowing it, I was pushing my body through these early warning signs, and that really shouldn’t be the case,” she told NutraIngredients.
“There’s a real lack of education around this, not just among athletes and exercisers, but also among coaches and medical professionals, and that lack of awareness can really delay the identification and treatment of these warning signs.”
Understanding RED-S
The term RED-S was introduced by the International Olympic Committee (IOC) in 2014 as part of a broader initiative to raise awareness about the impact of energy deficiency on athletes’ health and performance.
The IOC’s introduction of RED-S expanded upon the earlier concept of the ‘female athlete triad’, highlighting that energy deficiency can affect both male and female athletes and is accompanied by a range of physiological and psychological consequences beyond just reproductive and bone health.
“But like a lot of things in science and medicine, it takes time for research to filter into everyday practice,” Woolven said.
“Unfortunately, most general practitioners won’t have had any formal training on RED-S, simply because athletes are considered a small subset of the population, but we’re now starting to see that RED-S doesn’t just affect elite athletes, it impacts regular exercisers too, even those who don’t consider themselves athletes.
“That’s why it’s more important than ever to raise awareness and educate people at every level of sport and exercise.”
Impacts of RED-S
When the body does not consume enough energy, it shifts into conservation mode. In women, it downregulates the reproductive system, reduces estrogen production and disrupts the menstrual cycle, leading to irregular periods and reduced fertility. The body essentially signals that it is unsafe to reproduce and redirects energy to essential functions like movement, Woolven explained.
Estrogen supports bone strength, so when levels drop (especially in active young women), bone loss occurs— similar to what postmenopausal women face. This raises the risk of stress fractures, shin pain and chronic injuries. Low energy availability also weakens digestion, mood, concentration and the immune system. Over time, it lowers athletic performance and increases the risk of serious conditions like osteoporosis and heart issues.
Women can face heightened vulnerability to RED-S during key life stages such as adolescence, pregnancy and menopause when hormonal and developmental changes increase energy demands, as underfueling during these stages can cause long-term damage to bone and cardiovascular health.
Woolven noted that signs of RED-S include mood changes, low energy, disrupted sleep, poor performance and irregular menstrual cycles.
Nutrition targets for female athletes
When it comes to nutritional targets for female athletes, it starts with the basics: simply eating enough but also eating at the right times.
“Training in a fasted state can be risky for females because it adds stress to a system that is already sensitive to energy availability and hormonal shifts,” Woolen said.
“When you do not fuel your body, it has to pull from limited energy stores, which can disrupt the hormonal system, affecting estrogen and progesterone production, the key hormones for menstrual health, bone density, mood and overall well-being.”
Recent studies have shown that even within-day energy deficits such as going too long between meals or snacks can mimic the effects of an overall energy deficit. And while active lifestyle fueling is a growing trend among consumers, one overlooked key nutrient, particularly within active females, is carbohydrates.
“It’s crucial to ensure that carbohydrate intake isn’t too low, as carbohydrates are our primary source of energy for both training and recovery,” Woollen said.
“While there’s a lot of focus on protein in active consumer content, carbohydrate intake often gets overlooked, especially for women.”
She explained that much of the nutrition information for women has historically been based on research conducted on men. However, while men might be able to get by with a low-carb diet or even fasted training, the female hormonal system does not respond in the same way.
“We need to stay updated with research and shift the focus towards increasing carbohydrate intake for many women, as it helps maintain balance, fuels the body and supports hormonal health,” Woolven said.
NutraIngredients Women's Health Webinar
The upcoming NutraIngredients editorial webinar on Women’s Health will provide an essential overview for athletes, coaches and nutrition professionals on how to recognize and protect against RED-S. Attendees will hear from leading experts like Woolven, who are working to raise awareness, improve research and advocate for sustainable health practices in female health. Register now to join the Women’s Health webinar on April 17 at 3 p.m. CET.