More and more people are overweight or obese and at the same time more and more people do not sleep enough. Could there be a link? Scientists have studied this problem by asking participants to reduce their sleep, usually from 8.5h/day to 5.5 h/day. They then noted what and how much the participants ate, and measured any hormone or body weight changes. Most of them would now answer yes indeed, there is a link.
It is clear that nobody believes that you can sleep excess weight off, but not sleeping enough (less than 7 hours/day) can hamper your efforts to slim down or keep your weight under control.
At a first glance this looks unbelievable, as when you are awake for longer, you are going to spend more energy.
The energy you spend consists of 3 components:
1) what you need to keep your body going (your basic metabolic rate),
2) the amount needed to assimilate food,
3) the energy used for all kinds of exercise and activities.
When asleep, you will not eat or move and your basic metabolic rate is reduced by 20-30%. Scientists have calculated that sleeping 5.3h instead of 8h would increase the amount of energy you spend by 45 kcal/d.
However, it is here that your unconscious brain starts interfering. As we have seen in some previous posts (e.g. here or here), your brain wants to keep you safe and it therefore wants your energy balance to remain the same. The balance between the energy you take in and the energy you spend determines your body weight, and depends on genetic, psychological and behavioural factors. Even if it sets your body weight a bit too high for your health, your brain will be unwilling to change it, as anybody who has ever tried to lose weight knows only too well.
Experiments have shown that when you have not slept enough, your brain will stimulate you to eat more to compensate for the energy you have spent. Unfortunately, it will make you overdo it. It will do so by making food more rewarding, and the data show that you will tend to snack more and to choose more fatty and carbohydrate-rich food. This is easily done in our modern world where food is widely available.
It is easy to see how all this will put your best efforts to stay slim in jeopardy. Moreover, a study by Arlet Nedeltcheva showed that dieters who slept for only 5.5 h/day lost more lean body mass and less fat than dieters who slept for 8.5h. They also suffered more from hunger.
Researchers have also studied the effect of insufficient sleep on next day’s activities. Even though some of them have not observed any effect, most report more sedentary time and less vigorous workouts. The discrepancy might be due to the fact that some study participants were used to insufficient sleep, or to the short duration of some studies which could not capture the full effect on people who exercise a few times a week.
There are still plenty of questions to be answered, e.g. what is the effect of habit, is there a difference between men and women, is what scientists observe in a study the same as what happens in real life etc…We do not know either what the effect of physical exercise is: regular exercise improves your sleep, which would then influence your energy balance. Nevertheless, it is a good idea to make sure you have enough sleep!
JP Chaput and MP St-Onge. Increased food intake by insufficient sleep in humans: are we jumping the gun on the hormonal explanation? Front Endocrinol (Lausanne). 2014; Jul 15;5:116. doi: 10.3389/fendo.2014.00116. eCollection 2014 (accessed 26/08/2014).
A V Nedeltcheva, J M Kilkus J Imperial et al. Insufficient sleep undermines dietary efforts to reduce adiposity. Ann Intern Med. 2010; 153(7): 435-441.
P D Penev. Update on energy homeostasis and insufficient sleep. J Clin Endocrinol. Metab. 2012; 97(6): 1792-1801.
MP St-Onge. The role of sleep duration in the regulation of energy balance: effects on energy intakes and expenditure. J Clin Sleep Med. 2013; 9(1): 73-80.