How Sleep Loss Damages Metabolism

The truth about sleep deprivation and its impact on fat loss & metabolic health.

Sleep is a fundamental biological process for health, but honestly, we have just scratched the surface in understanding it. Its role extends far beyond rest and recovery, influencing cognition, immunity, emotions, and more. Among these, one critical aspect of health that sleep significantly impacts is metabolism. Metabolism encompasses all chemical reactions in the body that maintain life, including those that convert food to energy, repair tissues, regulate cellular pathways, and of concern to many of you... the end outcome of changes in body fat and body composition. So, what effect does this have?

Glucose & Insulin Metabolism

One of the most well-documented effects of sleep deprivation is its impact on glucose metabolism, or put simply, the regulation of your blood sugar and use of fuel. Sleep loss has been shown to decrease insulin sensitivity (increased insulin resistance), making one less able to bring glucose into cells, thus increasing circulating glucose levels. 

In a study published in The Lancet in 1999, Spiegel et al. found that partial sleep deprivation (4 hours per night for 6 nights) led to a 40% reduction in glucose tolerance, with raised cortisol (stress hormone) and sympathetic nervous system activity (the 'fight or flight' response). This small study prompted further investigations on this question, yet the field remains in its infancy, with a recent review by Duraccio et al. (2024) in the Journal of Physiology stating that:

Increasing total sleep duration, is an emerging and ecologically relevant intervention with significant potential to advance our understanding of the mechanisms underlying the association between short sleep duration and the risk of cardiometabolic disease.

Therefore, it seems that sleep deprivation is a likely contributor to poor cardiometabolic health, but whether this effect occurs at 4, 5, 6, or 7 hours of sleep per night remains unclear. From my personal reading of the evidence, it seems harm emerges primarily at < 6 hours per night, but at this time, it remains difficult to make strong claims, and those who do make very strong claims on sleep loss and health are probably running ahead of the evidence.

Appetite Regulation & Weight

Sleep loss is also linked to changes in appetite regulation, contributing to weight gain, and most of this have probably understood the reason after a poor night of sleep. There are two hormones we must mention. Ghrelin, often termed the "hunger hormone," stimulates appetite, while leptin, the "satiety hormone," signals fullness and suppresses appetite.

Inadequate sleep increases ghrelin and decrease leptin, leading to increased hunger and reduced satiety. A study by Taheri et al. published in PLoS Medicine in 2004 demonstrated that sleep-deprived individuals (5 hours per night) had 14.9% higher ghrelin and 15.5% lower leptin (8 hours per night) compared to those who were well-rested. This hormonal effect, alongside reduced willpower or regulation of impulses, can lead to increased intake of calorie-dense, hyperpalatable foods that contribute to weight gain.

Summary & Further Learning

Investing in good sleep hygiene—such as maintaining a consistent sleep schedule, creating a good sleep environment and wind-down routine, and managing stress—can be powerful strategies in getting your sleep in order.

There's a lot more to cover on this topic, including the effect of sleep on various other hormones, the physiology of sleep, and how to actually coach sleep (or get all the coaching strategies in order for yourself). If you'd like to learn more and really level-up your ability to help others improve their sleep and get better results with diet & exercise, check out our Sleep Coaching Course now.