Why Not Eating Enough Is Ruining Your Sleep: Endurance Athletes

A lot of endurance athletes struggle with sleep and immediately look to stress, caffeine, screens, or training load. All of those matter. But one of the most overlooked contributors to poor sleep in endurance athletes is simply not eating enough.

Sleep is not passive. It is an active recovery process that requires energy. When energy intake is consistently too low, the body does not prioritize deep recovery. Instead, it shifts toward survival.

Training is a stress. Fuel is the signal that tells the body it is safe to recover. When energy availability is low, the nervous system stays switched on. This often shows up as difficulty falling asleep, frequent waking during the night, or early morning awakenings, even when overall fatigue is high. Low energy availability has been shown to increase cortisol levels, particularly in the evening. Elevated cortisol directly interferes with sleep onset and sleep depth. Research in endurance athletes has shown that inadequate overall energy and carbohydrate intake is associated with higher overnight cortisol secretion and poorer sleep quality (Stellingwerff et al., 2019).

Carbohydrate intake plays a critical role here. Carbohydrates influence serotonin production, which is a precursor to melatonin. Melatonin is the hormone that regulates sleep timing and sleep depth. When carbohydrate intake is too low, melatonin production can be impaired, leading to delayed sleep onset and more fragmented sleep (Afaghi et al., 2007).

Many under fueled athletes describe waking up in the middle of the night feeling alert, restless, or suddenly hungry. This is not random. When liver glycogen becomes depleted overnight, the body responds by releasing stress hormones to mobilize energy. That hormonal response increases heart rate and nervous system activity, making it difficult to stay asleep or fall back asleep. Research has shown that low glycogen availability increases sympathetic nervous system activity during sleep, reducing overall sleep efficiency (Knuiman et al., 2018).

Poor sleep does not exist in isolation. Sleep disruption further impairs recovery, increases perceived effort, and worsens hormonal stress responses. This creates a feedback loop where under fueling leads to poor sleep, and poor sleep increases physiological stress, making recovery even harder to achieve (Samuels, 2008).

Importantly, athletes do not need to be losing weight for this to occur. Research on Relative Energy Deficiency in Sport shows that athletes with stable body weight can still experience hormonal disruption and impaired sleep when energy intake does not match training demands (Mountjoy et al., 2018). For endurance athletes, good sleep is not just about routines, supplements, or sleep hygiene. It starts with energy availability. If the body does not feel fueled, it does not feel safe enough to fully shut down.

Eating enough, especially in the hours after training and before bed, is not indulgent. It is a recovery strategy. One of the clearest signals to the nervous system that it can rest is knowing that energy is available. If you are training hard and struggling to sleep, the issue may not be your bedtime routine.

It may be time to take a look at your plate.