For access to all of our training, gear, and race coverage, plus exclusive training plans, FinisherPix photos, event discounts, and GPS apps, sign up for Outside+.
The best place to begin is to understand the fine line between health and performance. There are various trends purported to support health and longevity, right next to more extreme trends that claim to improve performance. When balancing these two worlds, remember that when you train, you are putting your body under purposeful stress—to create metabolic, muscular, cardiovascular, and skeletal adaptations—which usually results in a change of body composition. The stress is the breakdown, not the adaptation. The adaptation comes from progressive overload in tandem with recovery.
How many times have you heard the phrase “calories in, calories out” when it comes to weight loss? Or how often have you heard how fasted training and/or intermittent fasting are fantastic ways to lose body fat and gain lean mass? Regardless of biological sex, science shows otherwise. Across the board, there is an increasing body of evidence to indicate that it is not the amount of calories you consume in a day that affects body composition and health. For example, a research group in Copenhagen has been investigating male and female athletes’ low sex hormone concentrations, poor thyroid function, appetite hormone dysfunction, and increases in body fat despite their training loads. They have shown again and again that those athletes with dysfunction spend more time in the post-exercise catabolic (breakdown) state than those athletes who are healthy, even though their daily calorie intake would reflect energy balance (adequate calorie intake for health and training). In other words, even though their numbers were the same for a 24-hour period, they were taking those calories in at the wrong times. Another research group from the University of Georgia followed hourly and daily energy intake to determine effects on body composition of recreational athletes and also found that the longer periods with low to no food intake were correlated with greater percentages of body fat. Even across heavy training blocks if energy intake is not timed around training, there is an increased risk of endocrine dysfunction and body fat gain, despite the presence of high calorie-burning training.
Overall, the research across all levels of athletes is telling us that eating behaviors resulting in large energy balance deficits and/or more hours in a negative energy balance are counterproductive for achieving the desired lean body composition. Additionally, the longer an athlete spends in negative energy balance and in the post-exercise catabolic state, the greater the risk is for alterations in insulin sensitivity, leptin, and ghrelin responses (increasing the likelihood of weight gain), as well as sex hormone dysfunction, leading to low testosterone in men and menstrual dysfunction and amenorrhea in women.
As an athlete of any level, if you are walking that fine line between health and performance, the most important aspect is to fuel your body—and to do it at the right time. Low fuel intake during and around training sessions will inhibit your adaptive responses, reduce your body’s ability to lose body fat and gain lean mass, and increase your risk for stress fractures, poor blood glucose control, poor sleep, mood disturbances, and ultimately poor performance.
More On This Topic: How to Trim Weight While Still Crushing Training