In this article, our expert Dr. Kieron Rooney – reviews: Effect of sleep duration on dietary intake, desire to eat, measures of food intake and metabolic hormones: A systematic review of clinical trials, led by Samira Soltanieh From the Department of clinical nutrition and dietetics, Faculty of Nutrition and Food Technology, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
1) What was the high-level summary of the research?
Individuals that have their sleep disrupted or who report naturally shorter sleep duration are more likely to also eat more. It is difficult to pinpoint exactly what they eat more of, but in general, adults seem to snack on foods with higher fat content and teenagers on higher glycemic index (GI) sweet foods.
2) What did the study try to measure?
This study sought out as many studies as possible in which a person’s sleep duration and dietary habits were investigated. They then explored if there was any association between what people ate with how long they slept.
3) How was the study undertaken?
This study is referred to as a systematic review. The authors themselves did not implement a study in which they collected data from individuals with disturbed sleep. Instead, they searched for, identified, and synthesised studies that met their inclusion criteria, which had already been conducted by other investigators.
The authors found over 700 studies and ended up identifying 50 studies that reported both food intake and sleep duration; 43 of these studies were on adults. Once the review authors had found these studies, they looked at the dietary data to see what the individuals in those studies were eating, and, how long they slept for. They also looked for any studies that reported on hunger and/or appetite and any studies that may have measured hormones believed to influence what humans eat.
4) What did the study find?
The main result the authors focused on here was total energy intake. This was reported in 30 of the 50 studies they found. Most studies – 19 of the 30 – associated short sleep duration with a tendency to overeat. While some studies showed this was a result of eating larger meals other studies reported that it was a result of more snacks being eaten throughout the day. There was no clear indicator of which – larger meals or more snacks – was likely to be common in specific people.
There was also no clear indication as to which macronutrients – fat, protein, or carbohydrate – may have been contributing to the excess energy being consumed. The authors summarised the studies and suggested the extra energy was coming from either fat or protein rather than carbohydrates, yet the results were very much 50/50 on this. A big reason for the lack of clarity here is that the review included studies that induced sleep deprivation from as short as 1 night by keeping people awake with entertainment and keeping lights on all night compared to other studies in which sleep was restricted for over a month to only 6 hours a night.
5) Is there any other research out there that supports these findings or contradicts it?
Absolutely, a 2017 systematic review was published that looked only at studies in which sleep was partially disturbed with reduced hours in bed. That review contained only 17 studies but they were so similar in design that the authors performed a meta-analysis. This is where the individual study results from each study are mathematically combined for each intervention, rather than simply being summarised such as in the present study. The smaller but more mathematically robust systematic review reported that even just partial sleep reduction of a couple of hours a night resulted in much greater energy intake with no effect on energy expenditure which was then concluded to lead to weight gain.
6) How much weight should we give this research?
This study is interesting and contains nearly three times the number of studies as the 2017 paper. However, the results of these studies are summarised rather than analysed and as such are very much open to interpretation. Despite this, this study provides a great resource for the complete repository of studies investigating the association between our diets and our sleep duration.
7) What does this mean for your work/research/industry?
For me, I think this is interesting in the context of understanding why some people may find themselves eating more processed snacks than others. The big question that still needs answering is whether or not it is the disrupted sleep that promotes individuals to snack and eat more, or it’s the eating more that then disrupts sleep.
8) What’s the key takeaway for us to take from this research?
If you are looking for simple ways to cut your intake of processed high-energy snacks – get more than 6 hours of sleep a night!
9) Will you be doing anything differently because of this research?
Not so much differently – but perhaps I will start taking more sleep history surveys in my diet intervention studies.
Dr. Kieron Rooney completed his PhD in the Department of Biochemistry, within the Faculty of Science at the University of Sydney. Kieron’s primary interest focuses on conducting research and using this research to educate others on how what we eat, influences our metabolism.