Sleep deprivation: the consequences for your training and recovery

Sleep deprivation is not a matter of feeling tired. In people losing weight on an identical calorie deficit, sleep changed the result completely: on 8.5 hours of sleep, 1.4 kilos of the weight lost came from fat; on 5.5 hours, only 0.6 kilos did. The rest came from fat-free mass (PMID 20921542).

Same diet. Same deficit. Different body.

As far as I am concerned, that is the most underrated study in the entire fitness world.

What are the consequences of sleep deprivation?

Sleep deprivation hits four things that carry your training: your body composition, your hunger, your resistance to illness and your injury risk. The effects have been measured in controlled studies and are larger than most athletes suspect. They also stack across days.

Look at that second row again. You do not just get hungrier; your satiety hormone drops at the same time.

That is not a lack of discipline. That is a hormonal head start you took away from yourself.

Is 6 hours of sleep enough for an athlete?

Probably not. Six hours sits below the seven-to-nine-hour range the Hersenstichting uses for adults, and it is close to the durations where the studies above found their effects. You can function fine on six hours and still recover worse than you think.

Picture two lifters of 30, both 90 kilos, both cutting on 2,200 kcal. One sleeps 8 hours, the other 5.5. After eight weeks both are 5 kilos lighter, but the odds are good that the second one paid a bigger share of that out of muscle mass.

Your scale cannot see that difference. Your mirror at twelve weeks can.

Why do you not always feel the deficit?

Because you get used to the feeling. Your subjective read on your own alertness flattens out while your performance keeps sliding. That is what makes sleep deprivation sneaky: the measuring instrument you use, which is you, gets miscalibrated.

It is also why I tell people to write it down instead of estimating. Two weeks of logging bedtime and wake time says more than a feeling.

What does sleep deprivation show in your blood?

Consistently short sleep can go together with higher cortisol in the evening, a less favourable fasting glucose and lower testosterone. None of those values proves anything by itself. Together they can give context to a recovery that has stalled.

What sleep does to your hormones and blood sugar is covered in more depth in what poor sleep does to your hormones and blood sugar. If you stay tired despite good training, also look at tired despite good training.

Our 360 health blood test measures those values in one go. It does not tell you how you slept, but it does show what is happening around it.

Can you catch up on lost sleep?

Partly, and not fully. A long Saturday restores some of your alertness, but it probably does not restore everything you gave up, and it pushes your rhythm later. As an emergency brake it is fine. As a plan it is poor.

My advice: do not add seven hours on Sunday, add thirty minutes to each weeknight. That is less heroic and works better.

The full approach, including the sleep-debt table, is in better sleep for athletes. If you keep waking at night instead, start with waking up at night.

References

1. Nedeltcheva AV, Kilkus JM, Imperial J, et al. Insufficient sleep undermines dietary efforts to reduce adiposity. Annals of Internal Medicine. 2010. PMID 20921542.
2. Spiegel K, Tasali E, Penev P, Van Cauter E. Sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite. Annals of Internal Medicine. 2004. PMID 15583226.
3. Prather AA, Janicki-Deverts D, Hall MH, Cohen S. Behaviorally assessed sleep and susceptibility to the common cold. Sleep. 2015. PMID 26118561.
4. Milewski MD, Skaggs DL, Bishop GA, et al. Chronic lack of sleep is associated with increased sports injuries in adolescent athletes. Journal of Pediatric Orthopedics. 2014. PMID 25028798.
5. Leproult R, Van Cauter E. Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA. 2011. PMID 21632481.
6. Hersenstichting. Sleep and sleep deprivation. Accessed 2026.

Disclaimer

Every blood test result includes a professional assessment by a BIG-registered doctor. This article gives general information and is not a substitute for medical advice. For treatment decisions, discuss your results with your GP.