Fragmented Sleep Reduces 24h Fat Oxidation by > 50% - Not Getting a Good Night's Sleep Sets You Up For Obesity.

Image 1: It looks awkward, but sleep masks
and ear-plugs are effective, cheap and
save ways to improve sleep quality
(image from lackofsleepsymptoms)

I think you will be familiar with the idea that an insufficient amount of sleep has been found to correlate (! not induce !) with visceral obesity and other negative health markers (e.g. Strian. 2005). Now a study from a the Department of Human Biology, Nutrition and Toxicology Research Institute Maastricht (NUTRIM) at the University of Maastricht in the Netherlands found that not getting a good nights sleep or, in this particular case, waking up every hour, reduces the amount of fat you burn in a period of 24 hours by -52% (Hursel. 2011, cf. figure 1).

Other than in the initially mentioned epidemiological guesswork ... ah pardon, correlation studies, Hursel et al. had their 15 healthy male volunteers report to the laboratory twice (>2 weeks between the sessions of the randomized, single-blind cross-over study). During each visit, the subjects stayed for 48 h in a respiration chamber, where energy expenditure, physical activity (radar), and substrate oxidation were meticulously measured. On both occasions, the subjects had fixed bedtimes (lights out: 11:00pm; lights on: 7:40am) resulting in 8 h sleeping time per night. On one of the occasions, however, the scientists used induced sleep-fragmentation by the means of "approximately hourly wake-up calls" the subjects had to respond to by turning off their alarm after 2 min.

Figure 1: Relative differences in carbohydrate and fat oxidation, as well as respiratory quotient (higher quotient = more carbohydrate dependent) in 15 healthy men as a consequence of interrupted sleep (data calculated based on Hursel. 2011)

Diet-wise, the subjects who had been asked to abstain from strenuous exercise and to sleep for 8 h during the nights before their visit at the lab, were fed a standardized (protein:carbohydrate:fat ratio 12:55:33) diet consisting of "normal, everyday food products" two days before and in the course of their stay in a respiration chamber. The use of the latter, by the way, facilitated pretty exact measurements of the subjects energy expenditure and substrate oxidation (cf. figure 2).

Figure 2: Relative changes in total, resting (REE) and sleeping energy-expenditure (SEE), as well as absolute changes in activity induced energy expenditure (AEE) and overall caloric balance (data calculated based on Hursel. 2011)

As the data in figure 2 shows there was no statistically significant difference with respect to the overall calorie balances of the subjects (+0.41MJ/day to +0.41 MJ/day in the normal vs. the interrupted sleep group, respectively). While this appears counterintuitive as the recorded physical activity of the sleep-disturbed subjects had eventually increased, Hursel et al. point out that because of their study design, ...

we showed an initial increase in physical activity and AEE as an effect of sleep fragmentation, mainly because the subjects had to turn off their alarm clock 7 times during the night. However, the resulting increased exhaustion and sleepiness during the subsequent day might eventually counter-balance physical activity and AEE.

They go on to point out that the increased activity goes hand in hand with the increase in carbohydrate oxidation, the depletion of glycogen stores and the (this is my assumption) stress-related -52% decrease in fatty acid oxidation (cf. figure 1).

The real-world results of this unhealthy combination of non-regenerative sleep, daytime exhaustion and sleepiness and the accompanying abstract metabolic shifts are cognitive problems, a lack of motivation (esp. to work out or do any physical work), carb-cravings, snack-attacks & co... In your efforts to (re-)feed a body that is unable to access his well-stocked fat reserves, you end up overcompensate the initially increased energy expenditure, constantly provoking insulin spikes which totally blunt fat oxidation, trigger temporary hyperglycemia (if you are not already diabetic) and induce further snack-attacks. Thus, you are triggering a down-ward spiral that is especially hard to escape from, if your body does not get the chance to reset his insulin and stress levels in the course of a good nights sleep - keep that in mind before you place your cell-phone next to your pillow in order to "keep in touch" with your (facebook-)friends 24/7, as a very recent study published in the journal SLEEP showed that "mobile phone use for calling and for sending text messages after lights out was associated with sleep disturbances independent of covariates and independent of each other" (Munezawa. 2011).