Who haven’t heard of low carb diets, satiating effects of protein or importance of proper breakfast in weight management? A number of books and scientific papers are published in these subjects. There are hardly any books or guidelines which focus on sleep and its vital role on weight management. Let me explain.

Lack of sleep burns muscle rather than fat

The core objective of weight management is lose or prevent fat depositions. It is known fact that during weight loss also fat free mass, muscles are wasted. A fresh study demonstrates that sleeping circa 8 hours a night is a key means to secure effective fat burn and to prevent unnecessary muscle catabolism. This randomized trial showed that a sleep deficit of c. 3 hours per night (from 8 to 5 hours), in course of 2 weeks, causes muscle catabolism rather than fat burn during weight loss period. During 2 weeks’ weight loss sleeping sufficiently (8 hours/night) participants lost equal amount of fat and muscles, 1,5 kg respectively. When put on a sleep restriction of 3 hours/night (totaling 5 hours sleep/night), participants lost more muscles than fat (2,4 kg vs 0,6 kg respectively) (Nedeltcheva et al. 2010). In addition, during sleep restriction participants reported stronger feelings of hunger. This is a small study, but is in line with previous epidemiological trials.

Short sleep as risk factor for obesity

Associations between obesity and sleep length has been intriguing researchers for years. In a systematic review from 2008 (Patel & Hu 2008), it was concluded that obesity and sleep deprivation are linked. Investigators found all together 36 studies scrutinizing the associations. According to the investigators the association between lack of sleep and obesity is strongest among young.

Potential mechanisms?

Common sense would say that longer you stay up, more you burn calories. Common sense would also say that longer you stay up, more opportunities you have to consume more calories. I think sitting in the front of TV and exposure to the food ads late in the evening is one of the key things to play in here. Some studies have shown that those who stay up longer consume some 300 calories more per day than those who go in bed early.

Patel & Hu suggest the following explanations in their systematic review:

1. Lack of sleep increases fatigue which in turn lead to decreased physical activity
2. Lack of sleep disturbs the function of some key hormonal regulators of appetite. Ghrelin levels rise and leptin levels  decrease
3. Increased time awake = increased eating
4. Lack of sleep decreases thermogenesis, and therefore decreasing resting metabolic rate

There are studies that have shown that lack of sleep increases the levels of a key stress hormone, cortisol, during day and night (Omisade et al 2010). Cortisol is catabolic hormone that accelerates catabolism of muscles and increases fat deposition. This is quite opposite to what a weight watcher would want to experience. Finnish researchers have observed that visceral fat also tunes body towards stress and increases catabolism, similar to sleep deprivation (Marniemi J et al 2002) .Therefore, sleep deprivation and concomitant obesity compounds the stress hormone levels. It’s now also known that sleep deprivation causes insulin resistance already in week (Buxton OM et al. 2010). This is a further evidence underlining detrimental effects of sleep deprivation on body’s capacity to metabolize glucose, fat and protein.

Midnight shifts cause obesity

During the midnight shifts normal sleep patterns is lost. It is well known fact that midnight shift workers have more obesity than their controls (day time workers). Previously, it was thought that this might be explained simply by socioeconomic background factors. This is not the case. There is pretty strong epidemiological evidence showing that midnight shifts have at least 2-fold risk for obesity and metabolic syndrome when compared to daytime workers (for example, Chen JD et al 2010 or Antunes LC et al 2010). What might be the reason for this?

It has been demonstrated in several epidemiological studies that evening and night based dietary pattern is linked to obesity. Is evening eating deleterious? English general practitioner dr.Briffa pondered the issue in his blog. In his post, dr.Briffa describes how unnatural sleep and light pattern leads to distorted eating pattern which in turn causes obesity on mice (even if calorie balance is maintained). Now, experimental studies are applicable to humans, but surely give some food for thought.

Investigators at Harvard reported when participants in an intervention trial were shifted from day time work to night time work leptin levels fell 17 %, insulin levels increased 22 % and glucose increased 6 % (Sheer FA et al. 2009). Night shifts clearly disturb circadian rhythm and metabolic balance significantly. Of interest, a Finnish research team has also showed that shift work is linked to 2-fold increase in atherosclerosis among males less than 40 years.   (Puttonen S et al. 2009)

Lack of sleep is common

Here in Finland, length of sleep has decreased by 18 minutes during the last 30 years. Share of those who sleep less than 7 hours has increased whereas share of those sleeping more than eight hours have decreased (Kronholm et al. 2008). In addition to adults, Finnish children tend to sleep an hour less than their European peers (LATE -study). Finland performs badly in here. How is it in your country?

Conclusion

Already 2-3 hours sleep deficit during early night causes hazardous effects on metabolism, stress hormone levels, obesity and possibly catabolism. Night shifts seem to disturb metabolism and hormonal balance and lead to obesity. Sufficient, sound, natural timing of sleep are the foundations for sustaining cardiovascular health and healthy weight.

What do you think should we all start “sleep repletion”?

References

Antunes LC, Levandovski R, Dantas G, Caumo W, Hidalgo MP. Obesity and shift work: chronobiological aspects.Nutr Res Rev. 2010 Jun;23(1):155-68.

Buxton OM, et al. Sleep restriction for 1 week reduces insulin sensitivity in healthy men. Diabetes. 2010 Sep;59(9):2126-33. Epub 2010 Jun 2

Chen JD, et al. Obesity and high blood pressure of 12-hour night shift female clean-room workers. Chronobiol Int. 2010 Jan;27(2):334-44.

Kronholm E, et al. Trends in self-reported sleep duration and insomnia-related symptoms in Finland from 1972 to 2005: a comparative review and re-analysis of Finnish population samples. J Sleep Res. 2008 Mar;17(1):54-62. Review.

Marniemi J, et al. Visceral fat and psychosocial stress in identical twins discordant for obesity. J Intern Med. 2002 Jan;251(1):35-43.

Nedeltcheva AV, et al. Insufficient sleep undermines dietary efforts to reduce adiposity. Ann Intern Med. 2010 Oct 5;153(7):435-41.

Omisade A, et al. Impact of acute sleep restriction on cortisol and leptin levels in young women. Physiol Behav. 2010 Apr 19;99(5):651-6. Epub 2010 Feb 4.

Puttonen S, et al. Shift work in young adults and carotid artery intima-media thickness: The Cardiovascular Risk in Young Finns study. Atherosclerosis. 2009 Aug;205(2):608-13. Epub 2009 Jan 21.

Patel SR, Hu FB. Short sleep duration and weight gain: a systematic review. Obesity (Silver Spring). 2008 Mar;16(3):643-53. Epub 2008 Jan 17. Review.

Scheer FA, et al. Adverse metabolic and cardiovascular consequences of circadian misalignment. Proc Natl Acad Sci U S A. 2009