I doubt anyone would argue that sleep is fundamental to health and wellbeing. Sleep is the time where our mind and body recovers from today and prepares for tomorrow. We know poor sleep is associated with worsened immune and cognitive function. And from an athletic standpoint, we know that lack of sleep correlates with increased injury risk (see Watson, 2017), and can impair psychomotor reactions and increase perception of effort and fatigue … both of which have the potential to impact athletic performance.
Despite its importance, sleep is something many of us struggle with. Whether it is having enough time in the day to get the sleep we need, to trouble falling asleep, to trouble staying asleep when we get to bed. Work, family and social commitments plus, for athletes, the physical and mental stresses of training, travel, and competitions might all challenge the quantity and quality of sleep we can get (Gupta, Morgan and Gilchrist, 2017). And reciprocally, lack of sleep can make each of these things more challenging, physically and mentally.
And it is the same with diet. Sleep can impact our appetite and food choices, and our dietary choices can impact our sleep. So, how?
p.s. I have included mainly reviews in the references, simply to simultaneously provide info on where to read more broadly on the topic. References to the underlying research can be found reading each of these reviews.
The impact of sleep on diet
We know poor sleep is correlated with increased incidence of obesity (see Burrows, Fenton and Duncan, 2020). However, correlation is not causation. It could be that obesity causes poor sleep. Or it could be a vicious circle where poor sleep drives obesity, which drives poor sleep, which … and so on. Or both could be caused by another factor entirely, such as stress.
Having said this, sleep does seem to impact both our food preferences and how our body uses food. In ways that could result in weight gain over the long term. In many ways sleep deprivation appears to have many of the same effects on appetite and food choice as stress, which I wrote about in my previous blog.
First, appetite. Overall, studies show that reducing sleep by just 2-3 hours per night can increase the amount of ghrelin (a hormone that makes us feel hungry) and reduce the amount of leptin (a hormone that makes us feel full) in our bodies. So, we may feel hungrier and want to eat more (see Golem et al., 2014). On top of this, poor sleep seems to increase the centres in the brain that respond to food intake such that we feel a heightened sense of ‘reward’ when we eat. So, potentially leading us to overeat. And consistent with both these triggers, evidence does suggest we are more likely to eat more calories following a night of poor sleep … and more calories than would compensate for the increase in calories we burnt by being awake longer the previous day (see Golem et al., 2014; see St-Onge, Mikic and Pietrolungo, 2016).
Second, food choices. Like stress, lack of sleep seems to heighten our sense of reward not just for any old food, but for high sugar and high fat foods. And reduces our inhibitory control, i.e. our ability to resist things that trigger such feelings of ‘reward’. Consistent with this, multiple studies have now shown that we are more likely to choose such foods when sleep deprived (Greer, Goldstein and Walker, 2013; see St-Onge, Mikic and Pietrolungo, 2016; see Flanagan, 2020).
And then in terms of metabolism, chronic poor sleep seems to drive some level of insulin resistance (again, similar to stress). This means that we may not be able to use blood sugar so well for energy, may not control blood sugar levels so well, and need more sugar intake before our brain realises we have ‘enough’ so to speak (see Golem et al., 2014). On top of this, we typically eat more food later at night when we are not sleeping. And it seems that food intake close to when our body is signalling we should be about to sleep (by the rise in the hormone that helps us fall asleep, melatonin, that happens at night) also impairs how we use and tolerate sugar (see Flanagan, 2020). And this appears to be associated with weight gain. In fact, it is thought that eating through the night may be one reason that shift workers are at higher risk of weight gain even when they don’t appear to eat more food than your average ‘day shift’ worker.
The impact of diet on sleep
We are generally less certain about the impact of diet on sleep … because studies have mixed findings and there are fewer studies overall.
We often think that low calorie diets can stop us sleeping so well, both in terms of how long it takes us to fall asleep and then staying asleep with enough deep sleep. Actually, studies have shown that short term calorie restriction doesn’t seem to impair sleep so much. However, long term low calorie diets that lead to low energy availability in the body do seem to impair sleep (see studies on ‘Low Energy Availability’ in athletes and the review by Mountjoy et al. 2018).
In terms of specific foods and food groups, there is some evidence that high carbohydrate intake within a few hours of sleep time can decrease the amount of time we spend in slow wave sleep, which is the ‘deepest’ part of sleep. But also that eating high carbohydrates, particularly fast digesting high glycaemic index carbohydrates (like sugar) can reduce the time it takes us to fall asleep. So, potentially a negative and a positive to overall sleep quality there … and which is the dominant effect is not yet clear (see St-Onge, Mikic and Pietrolungo, 2016).
And then there is tryptophan and melatonin. I mentioned earlier that melatonin is the hormone that helps us fall asleep. Melatonin is made in the body from tryptophan, an amino acid. Pharmacological doses (i.e. as would be bought or prescribed in a tablet) of both tryptophan and melatonin do have a positive impact, at least on how long it takes us to fall asleep. However, foods high in these don’t necessarily have the same impact … studies in things like milk, tart cherry juice and kiwis have mixed findings! And the doses of both of these are certainly just so much lower in foods than they are in a prescription. See Frank et al., 2017 for more.
What we do know is that both caffeine and alcohol can impair sleep (Flanagan, 2020). Caffeine, because it is a stimulant that acts on parts of the brain that regulate sleep / wake. The effects are variable between individuals, as we all differ in how sensitive we are to the effects of caffeine. But you can easily give it a test … if you alter your caffeine intake do you find it easier or harder to sleep! And alcohol is a depressant that – whilst you can fall asleep quite easily – is associated with disrupted sleep patterns through the night.
Summary and future perspectives
Sleep impacts diet, and diet can impact sleep. That much appears clear. But research is equivocal and much of it is observational. More work is needed to understand the causes of these effects … because an understanding of these can help us to better understand how to tackle the issues (aside from trying to improve our sleep through strategies from improved sleep hygiene to meditation).
And from a sports nutrition perspective, there have been very few studies looking at the interaction of sleep and diet in athletes. There is a very real possibility that there may be differences between athletes and the general population, as factors such as high training volumes and timing of training may interact with sleep to impact food preferences and how the body responds to food at different times of day.
References
Burrows, T., Fenton, S., and Duncan, M. (2020). Diet and sleep health: a scoping review of intervention studies in adults. Journal of Human Nutrition and Dietetics, accessible at https://doi.org/10.1111/jhn.12709
Flanagan, A. (2020). How sleep and nutrition interact. Sigma. See https://sigmanutrition.com/sleep-nutrition/
Frank, S., Gonzalez, K., Lee-Ang, L., Young, M.C., Tamez, M., and Mattei, J. (2017). Diet and sleep physiology: public health and clinical implications. Frontiers in Neurology, 8, 393.
Golem, D.L., Martin-Biggers, J.T., Koenings, M.M., Finn Davis, K., and Byrd-Bredbenner, C. (2014). An integrative review of sleep for nutrition professionals. Advances in Nutrition, 5, 742 – 759.
Greer, S.M., Goldstein, A.N., and Walker, M.P. (2013). The impact of sleep deprivation on food desire in the human brain. Nature Communications, 4, 2259.
Gupta, L., Morgan, K., and Gilchrist, S. (2017). Does elite sport degrade sleep quality? A systematic review. Sports Medicine, 47, 1317 – 1333.
St-Onge, M.P., Mikic, A., and Pietrolungo, C.E. (2016). Effects of diet on sleep quality. Advances in Nutrition, 7, 938 – 949.
Watson, A.M. (2017). Sleep and athletic performance. Current Sports Medicine Reports, 16 (6), 413 – 418.