Underfueling and Cholesterol: A Hidden Risk for Endurance Athletes
Please note that there are references to calories and eating disorders, so read with care.
In this article, I’m going to review how and why endurance athletes can be at risk for altered cholesterol levels. This is a nuanced topic that demands some in-depth explanation and background. Here are the high-level key points, but I encourage you to read on for the full story.
Endurance athletes, for various reasons, are at high risk for “low energy availability” (LEA) and Relative Energy Deficiency in Sports (REDs) aka not eating enough. In a recent study, 43% of runners were at risk for LEA (1).
When faced with a significant and sustained caloric deficit, the body and nervous system will prioritize essential functions (such as heart and brain function). When this occurs, other also essential systems go haywire. These include the endocrine system (hormones), gastrointestinal function, metabolism, and the building and repair of bones, muscle, and tissues.
Through a complex cascade of events, this can result in altered metabolism and cholesterol levels, leading to either elevated or irregular cholesterol levels you wouldn’t expect in someone who “eats healthy and exercises.”
If unaddressed, altered cholesterol levels can significantly increase your risk of heart disease and long-term health complications
Now, here’s the full story…
why endurance athletes may be at risk
Endurance athletes are often held up by society as models of picture-perfect health. Endurance exercise is ingrained in our societal health narratives, evidenced by the fact that one of the most common ways people try to jumpstart a new health-related routine is by signing up for a running race, triathlon, or other endurance-related event. At EVOLVE, we tend to get more pushback from our patients and clients when we try to encourage resistance training compared to cardiovascular and endurance exercise.
Side note: This should go without saying if you’ve followed EVOLVE for any period of time, but “healthy” doesn’t have a look or a body type. “Health” is a nebulous idea dependent on your personal goals and values, not a definitive destination, and certainly not related to how much you weigh.
However, as a registered dietitian with over eight years of experience working with endurance athletes and eating disorders, I commonly work with athletes who, despite impressive feats of endurance, are having health-related problems, including:
Elevated or altered cholesterol levels
Hormonal disruptions
Gastrointestinal issues
Stress fractures or bone injuries
Other recurrent overuse injuries
Mental health challenges
My work with eating disorders has illuminated many parallels between disordered eating behaviors and the nutrition challenges faced by endurance athletes. It is well-known that eating disorders like anorexia nervosa, and the associated effects of starvation, can negatively impact cholesterol and disrupt the natural physiology of the body. Fun fact, did you know that eating disorders don’t have a “look” and only 6% of those with eating disorders are clinically underweight? (2) I say this because someone could look “healthy” and have serious underlying health conditions. On the other hand, someone could exist in a large or fat body, and be completely physiologically healthy, but that is a story for another time.
Many endurance athletes, such as marathoners, ultra-marathon runners, cyclists, and triathletes, are vulnerable to a similar pattern of under-fueling, which can lead to harmful metabolic consequences, including elevated cholesterol.
I am not suggesting that all endurance athletes suffer from anorexia (although nearly 43% are at risk for disordered eating) (1). However, under-fueled endurance athletes can have similar issues as patients with anorexia, but these issues often go unaddressed by healthcare providers, potentially because providers, like society at large, assume that endurance athletes are not at risk for many health issues, such as altered cholesterol levels. Because of this, if a medical provider finds something amiss in an endurance athlete’s labs, they are often at a loss about what to do and go through the same old adage “eat better and exercise more”, because in the majority of people, increasing nutrient-dense foods, fiber, and focusing on sustainable movement and exercise behaviors improves most health markers.
Why is under-fueling a problem?
REDs Health Conceptual Model. The effects of LEA exist on a continuum. While some exposure to LEA is mild and transient termed adaptable LEA (arrow depicted in white), problematic LEA is associated with a variety of adverse REDs outcomes (arrow depicted in red). *Mental Health Issues can either precede REDs or be the result of REDs. LEA, low energy availability; REDs, Relative Energy Deficiency in Sport. (3)
One of the major concerns arising from this underfueling is Relative Energy Deficiency in Sport (REDs), a condition that affects metabolic function and overall health. REDs is a syndrome resulting from low energy availability (LEA), which occurs when there is insufficient caloric intake to meet both the energy demands of exercise and the physiological needs of the body. For the remainder of this article, you can interpret the phrase “low energy availability” as essentially synonymous with “not eating enough” or “not enough calories.”
I’ll also note that REDs evolved from the Female Athlete Triad (a condition characterized by LEA, menstrual dysfunction, and low bone density). This was broadened to include athletes of all genders and highlighted that energy deficiency affects numerous systems in the body, not just reproductive and bone health.
REDs can lead to a number of issues in the body, including impaired basic metabolic and immune system function, hormonal imbalances, decreased bone density, increased risk of overuse and other injuries, and mental health disorders. It affects essentially every system in the body because every body system needs energy (calories) to work properly.
Amidst all of this, what many fail to recognize is that REDs, while often associated with undernutrition and hormonal imbalances, can also influence cholesterol levels, leading to elevated levels of low-density lipoprotein (LDL) often referred to as “bad” cholesterol, and increased cardiovascular risk. (4) I don’t like using the terms “good” or “bad” but I’ll use it here because that’s likely how you have heard it described.
Why are endurance athletes at risk for under-fueling?
Endurance athletes are at high risk of under-fueling for a variety of reasons. These are the most common that I see in my patients:
Caloric expenditure of training: Depending on the type and duration of training, an endurance athlete can burn an entire day’s worth of calories in a training session, requiring a substantial amount of calories to maintain energy balance.
Number of training hours: It is not unheard of for non-professional endurance athletes to spend anywhere from 10-30 hours per week training. More is often seen as better in the endurance world. This time equates to greater caloric demands from the activity itself and also reduces the amount of time, motivation, and energy someone has in a day to cook and eat regular meals and snacks.
Desire to maintain a low body weight: Many endurance athletes believe that lower body weight enhances performance, particularly in activities such as running or cycling, where body mass could influence speed. (Note: This equation works on paper, but breaks down quickly when we apply it to human physiology. Losing weight while training may improve performance for a very short period of time, but it is also associated with injury, muscle loss, fatigue, and decreased performance, rather than any perceivable long-term benefit.).
Inaccurate energy intake calculations: Athletes often underestimate the number of calories they need to consume to offset the energy expended during long training sessions.
Gastrointestinal issues: Intense endurance exercise can impair digestive function, making it difficult for athletes to consume enough food before, during, and after workouts.
Psychological pressures: Disordered eating behaviors, rigidity around food intake and training, and an obsession with “clean eating,” is likely a recipe to guarantee you’re chronically underfueled.
Work and life outside of training: Most endurance athletes are not professional athletes, and are juggling the demands of training with full-time jobs, family, and other life responsibilities. This makes it logistically difficult to eat enough and can exacerbate any or all of the prior factors.
The short to long-term effects of REDs.
As a result, endurance athletes are highly vulnerable to chronic LEA, which can lead to REDs and their related health complications.
I will also note that REDs is a grouping of syndromes and exists on a spectrum, rather than a binary diagnosis. Issues can arise in the early days of under-fueling, and then compound over weeks, months, and even years. Full recovery is typically months to years, depending on the severity of symptoms and the duration of time that the athlete was in a state of LEA.
The Link Between REDs and Cholesterol Levels
Cholesterol is complex, confounding many highly qualified physicians and experts. I won’t pretend to know every nuanced detail relating to cholesterol physiology, but there are clear connections between cholesterol levels and REDs that are overlooked and essential to the long-term health of endurance athletes.
A quick cholesterol primer, although this information is available in much more detail elsewhere:
Cholesterol is essential for life. It is a precursor to essential hormones and is involved in repairing cells, cell communication, and cell structure.
There are various types of cholesterol particles, including low-density lipoprotein (LDL), very low-density LDL (VLDL), and high-density lipoprotein (HDL) cholesterol.
Consumption of cholesterol in food does not significantly impact the cholesterol levels measured in your blood. Instead, dietary fat intake—whether too much or too little—and fiber intake directly influences cholesterol levels. Additionally, metabolic health and exercise play a larger role in regulating cholesterol.
Altered cholesterol levels, especially elevated LDL levels, can significantly increase the risk of heart disease and other serious health issues. There’s more to the story here regarding what types of cholesterol are linked to negative health outcomes, but that’s a topic for another day.
Cholesterol levels strongly influence essential hormones in the body, specifically: estrogen, testosterone, and thyroid hormones.
Cholesterol levels are also strongly linked to how the liver functions in low-energy states.
Inflammation and oxidative stress affect cholesterol levels as well.
How does under-fueling or REDs cause altered cholesterol levels?
From the bullet points above, you can hopefully appreciate that cholesterol is complex, and many different body systems rely on cholesterol.
From just that alone, we can surmise that LEA, which affects all body systems, will likely affect cholesterol, which is also involved in many body systems. But let’s go a bit deeper.
Low Hormone Levels: LEA often leads to low testosterone, estrogen, and low or altered thyroid hormone levels. This can cause many issues such as impaired sexual function, mood disturbances, low energy and recovery, and a loss of bone density. It can also affect cholesterol:
Estrogen promotes the synthesis of HDL (“good cholesterol”) and limits LDL production. Estrogen is often low in athletes who are under-fueled, affecting cholesterol.
Testosterone is also linked to the suppression of LDL production, along with muscle growth and repair, and the utilization of fat for energy. Low testosterone, like estrogen, can affect cholesterol levels.
Thyroid hormones play a role in the clearance of LDL from the bloodstream. LEA can cause low thyroid levels, increasing relative blood levels of LDL.
Energy Production from the Liver: A reduced intake of carbohydrates and overall calories disrupts the production of adenosine triphosphate (ATP), the body’s primary energy molecule for most cellular functions. To compensate, the liver meets energy demands by utilizing fats, including triglycerides and cholesterol, which can lead to:
Increased LDL production, which transports cholesterol to tissues for energy use and cellular repair, even when the body doesn't need it. Over time, this excess cholesterol accumulates in blood vessels, raising the risk of cardiovascular disease.
Decreased HDL production, as the body deprioritizes the production of molecules responsible for removing excess cholesterol from the bloodstream and delivering it back to the liver for disposal.
If you’re more of a visual person, here is a rough graphic that shows this mechanism under normal and altered circumstances.
Inflammation and Oxidative Stress: Endurance athletes may have higher levels of oxidative stress due to prolonged periods of intense exercise. In athletes with REDs, oxidative stress becomes exacerbated. One of the most inflammatory things you can do for your body is not providing it adequate nutrients, thus if you’re body is in a constant state of breakdown, without the essential nutrients to repair, this results in more inflammation. This increases the oxidation of LDL cholesterol, transforming it into a more damaging form known as oxidized LDL, which is highly associated with arterial plaque formation and possibly heart disease.
Additionally, chronic energy deficiency leads to heightened inflammation, which further impairs lipid metabolism and promotes higher LDL levels, putting further strain on the cardiovascular system.
Entire textbooks have been written about these mechanisms and pathways. Personally, as a dietitian, I spent years studying these complex pathways in my undergraduate and graduate schooling. This article is not intended to be a biochemistry lesson, but hopefully it gives you a general insight into the myriad of ways that LEA can affect cholesterol levels.
It is also important to note that altered cholesterol levels can compromise athletic performance. Elevated LDL cholesterol, especially for a prolonged period, contributes to the development of arterial plaque, which impairs blood flow and reduces oxygen delivery to working muscles. For endurance athletes, diminished oxygenation can decrease stamina and prolong recovery times.
Therefore, the cardiovascular strain associated with high cholesterol undermines long-term endurance capacity and can put athletes at risk for serious conditions such as cardiovascular disease and strokes.
Practical Solutions for Athletes
Given the interconnectedness of REDs and elevated cholesterol, endurance athletes must take measures to ensure they are fueling appropriately to meet both their performance and health needs. Some practical strategies include:
1. Adequate Energy Intake
Athletes should regularly monitor their energy expenditure and adjust their caloric intake accordingly. While precise caloric needs will vary, most endurance athletes will require at least 2,500+ calories per day, depending on the intensity and duration of training. Working with a dietitian who specializes in athletes can help you better understand their individual needs.
At the risk of being redundant, I cannot stress enough that the vast majority of endurance athletes underestimate their caloric needs and don’t take eating enough as seriously as they should. Given the negative consequences of under-fueling and the benefits of proper fueling for performance, I believe that eating enough is perhaps the most important aspect of endurance training—more important than any specific training plan.
2. Balance of Macronutrients
A well-balanced diet that includes enough carbohydrates, proteins, and fats is vital for preventing REDs and managing cholesterol levels. Carbohydrates should make up about 45-65% of total caloric intake because they provide glucose, the primary fuel for endurance activities. Dietary fats, especially omega-3 fatty acids found in fish, nuts, and seeds—should also be included, as they promote a better lipid profile by raising HDL cholesterol and potentially reducing LDL.
Given societal and diet culture narratives, many endurance athletes that I work with are hesitant to eat carbohydrates, when carbohydrates are what their body truly needs to maintain health and fuel performance.
3. Regular Blood Testing
Athletes should undergo regular medical evaluations to monitor cholesterol levels, hormone profiles, and thyroid function, particularly if they are at risk of REDs. Early detection of hormonal imbalances or elevated cholesterol can lead to timely interventions and the prevention of long-term health complications.
4. Rest and Recovery
Proper recovery is essential to avoid energy deficits and the detrimental effects of REDs. Athletes should prioritize nutrition, sleep, rest (1-2 rest days a week), and consider periodizing their training plans to allow for sufficient recovery.
In summation…
Eating enough calories, carbohydrates, and dietary fat is essential for proper metabolic function and preventing complications like REDs. Even if an athlete doesn’t suffer from full-blown REDs, insufficient caloric intake can result in decreased performance, increased injury risk, and, yes, altered cholesterol levels. Lighter is not necessarily faster, and at EVOLVE, we strongly believe that your overall lifelong health is more important than your race performance, especially if you are not a professional athlete. Not eating enough can have serious long-term mental and physical health consequences. A well-nourished, well-rested, and well-trained athlete will always outperform an athlete chasing an unrealistic “race weight.”
If you made it this far and read the entire article, you probably need a snack, as focused mental effort takes calories too! If you’re concerned or have further questions you can book a session with one of our Registered Dietitians. Happy snacking!
Henninger K, Pritchett K, Brooke NK, Dambacher L. Low Energy Availability, Disordered Eating, Exercise Dependence, and Fueling Strategies in Trail Runners. Int J Exerc Sci. 2024 Jan 1;16(2):1471-1486. PMID: 38288400; PMCID: PMC10824294.
Varga TV, Ali A, Herrera JAR, Ahonen LL, Mattila IM, Al-Sari NH, Legido-Quigley C, Skouby S, Brunak S, Tornberg ÅB. Lipidomic profiles, lipid trajectories and clinical biomarkers in female elite endurance athletes. Sci Rep. 2020 Feb 11;10(1):2349. doi: 10.1038/s41598-020-59127-8. PMID: 32047202; PMCID: PMC7012926.
Mountjoy M, Ackerman KE, Bailey DM, et al2023 International Olympic Committee’s (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs)British Journal of Sports Medicine 2023;57:1073-1098.
Flament MF, Henderson K, Buchholz A, et al. Weight Status and DSM-5 Diagnoses of Eating Disorders in Adolescents From the Community. Journal of the American Academy of Child & Adolescent Psychiatry. 2015;54(5):403-411.e2. doi:https://doi.org/10.1016/j.jaac.2015.01.020.