If you’re consistently burning more calories than you are eating, you could be setting yourself up for failure as an athlete, weight gain and injury.
There are few things more satisfying after a tough workout than glancing at your watch or odometer and gauging how many calories you’ve torched with your efforts. Undue gym selfies and “humble brags” on social media are a testament to how much we love a good calorie burn session.
In addition to taking great satisfaction in the calories we expend, we also tend to agonize over the calories we consume. Taking in too many calories is a constant worry for those trying to lose or maintain their weight. For athletes who are trying to improve their speed by reaching their “ideal” racing weight, the oft-touted “calories in versus calorie out” can quickly become a recipe for excessive exercise and under-eating. Instead of a performance boon, this often has the opposite effect, leaving athletes run-down and injured and can even compromise their long-term health.
Low energy availability (LEA) occurs when energy consumed is exceeded by energy expended through exercise and lifestyle, resulting in short-term or long-term caloric deficits. LEA may be the result of intentional dieting—a means to achieve a lower body weight for aesthetics or competition, or it may be due to an eating disorder. This is especially true in sports like track and field, distance running, biking and triathlon where low body weight confers a performance advantage.
In athletes, LEA can also be unintentional due to the large energy demands of high-volume training. Ironically, this is more prevalent among athletes committed to eating healthy. The staples of a “healthy” diet tend to be lower in energy-density, making it difficult for athletes to eat enough to support their elevated energy expenditure.
LEA in athletes has historically been seen as an issue primarily affecting females. The “Female Athlete Triad,” a syndrome characterized by irregular menstruation, low energy availability and low bone density, has been widely studied, particularly in female endurance athletes. However, LEA and the resulting negative performance and health affects impact men as well. In fact, one study found clinical LEA in 58 percent of male endurance athletes compared to 51 percent of female endurance athletes. In recognition of this finding, Relative Energy Deficiency in Sports (RED-S) syndrome is now a more inclusive term to identify the LEA that can alter metabolism, hormones, bone health, immunity, protein synthesis and cardiovascular and psychological health.
To understand why LEA can be so detrimental to health and performance, it is first helpful to grasp where this imbalance stems from. Everyone, athlete or not, has unique energy requirements. There are three components that determine one’s daily energy needs: basal metabolic rate, thermic effect of food and physical activity.
Basal metabolic rate is the energy our body requires to perform the basic functions of living such as breathing, circulation and thermal regulation. Basal metabolic rate is affected by a number of factors out of our control—age, genetics, gender and hormones—as well as those that we can influence, including skeletal muscle mass, caffeine intake and environmental temperature. Metabolic rate can be estimated using predictive equations or measured in a laboratory setting.
Thermic effect of food is simply the calories required to digest and absorb the food we consume. Its relative contribution to our total daily energy needs is so negligible that it is rarely accounted for.
Physical activity is the most highly variable when it comes to predicting one’s energy needs as it can range from just a few hundred calories for a sedentary individual to thousands of calories for those engaging in high-volume or high-intensity training.
When our energy intake is mismatched with our energy requirements we will either gain weight (if consuming more calories than we require), or lose weight (if consuming fewer calories than we require). Logic would suggest that the fewer calories we consume and/or the more we burn off, the faster we lose weight.
Not so much.
From an evolutionary perspective our bodies don’t like losing weight. Extra body fat was essential for survival when food was scarce for our hunter-gatherer ancestors. Thus, our bodies are designed to hold on to body fat and burn fewer calories when there is too great a disparity between our intake and expenditure. This is just one of many adaptations that kick in when our calorie consumption gets too low. Although the physiological impacts of LEA are still not fully understood, what we have found so far is hardly desirable.
To start with, both men and women experience a reduction in sex hormones. In females this can result in irregular periods and reduced fertility. Less is known about what hormonal repercussions exist for males with LEA, however lower testosterone levels have been measured in endurance male athletes with LEA. Low testosterone levels are associated with reduced muscle mass and fatigue; hardly ideal outcomes for male athletes.
These reduced hormone levels also negatively impact bone health in both males and females. This is particularly concerning for athletes participating in impact sports like running where bone stress injuries are common. Studies have shown that bone mineral density, a measure of bone health, is lower in male and female runners with lower body weights. Perhaps more concerning is that independent of bone mineral density, athletes with lower testosterone levels had a greater risk for bone stress injuries.
Runners aren’t alone in their concerns over bone health. Numerous studies have found that cycling, a non-weight bearing sport, can also be associated with lower bone mineral density. LEA likely compounds this effect.
In a 2018 study of 50 competitive cyclists, researchers found that those with LEA had the lowest bone mineral density of the group. Additionally, the cyclists with LEA were less responsive to training. Essentially, they were putting in the same amount of time and effort, but with poorer performance outcomes than the study participants who were consuming adequate calories.
Perhaps most concerning is the long-term affect LEA has on basal metabolic rate. As mentioned previously, our body resists weight loss. By reducing its basal metabolic rate it is able to prevent drastic weight loss.
Unfortunately, this reduction in metabolic rate is not transient. Studies have shown that those with extended periods of LEA experience an irreversible reduction in metabolic rate that makes it increasingly difficult to maintain a lower body weight. This is why many who lose a significant amount of weight through crash dieting gain back the weight they have lost, plus additional pounds, after returning to their old eating habits.
Clearly, we’ve established that LEA isn’t ideal for health or performance, but simply acknowledging this isn’t necessarily enough to avoid or correct it. Those who recognize they are at risk due to a demanding training schedule or a tendency to be restrictive with food intake should work with a professional to estimate their energy requirements for optimal health and performance. Whether you are training for your first 5K or setting out to traverse the Long Trail, food is fuel and although calories can at times feel like the enemy, they are what power us for the activities we love.
Jamie Sheahan is the Director of Nutrition at The Edge in South Burlington. Jamie holds a Master of Science in Dietetics from the University of Vermont, where she serves as an adjunct professor of sports nutrition. Jamie has run over 40 marathons in addition to several ultra marathons.
Featured Photo Caption: A 2018 study of 50 competitive cyclists found that those with LEA were less responsive to training.