Are sleep and weight somehow connected?
Can too little sleep make weight loss more difficult?
Even worse, can insufficient sleep lead to fat and weight gain?
These are some of the questions we regularly receive from our readers and which we’ll answer in this article.
Let’s get right to it!
Sleep and weight: a consistent connection
As you will have already guessed, sleep and weight are definitely connected. This is supported by a number of high-quality studies, as well as by several scientific reviews.
The association between sleep duration and body weight is, of course, an inverse one, with research showing that people who get too little sleep suffer from higher rates of obesity.
In this systematic review and meta-analysis of a total of 24,821 children and adolescents, for example, it was found that short sleep duration in young people is significantly associated with future overweight/obesity.
Metabolic Syndrome (the name for a group of risk factors including increased blood pressure, high blood sugar, excess body fat around the waist, and abnormal cholesterol or triglyceride levels) has also been found to be linked to sleep duration.
For example, this 2014 systematic review and meta-analysis which included almost 90,000 participants, found that short sleep duration was significantly associated with risk of metabolic syndrome (MS).
According to the authors, “since obesity, hypertension and impaired fasting glucose are components of MS, it is not surprising that short sleep duration was positively associated with MS”.
Take-away point: sleep and weight are definitely connected, with research showing that insufficient sleep is positively and significantly associated with a higher risk of overweight and obesity.
How does too little sleep cause fat gain?
Overall, the scientific literature supports an association between sleep and weight, with most research showing that shorter sleep duration is correlated with increased body weight.
What is not entirely clear, however, is whether the relationship between sleep and weight is a causal one; that is whether one of the variables changes as a result of a change in the other variable.
Unfortunately, although a number of limitations in the design of studies make it difficult to know with certainty if there is, indeed, a causal relationship, we can draw some conclusions from the available experimental studies on sleep deprivation.
So here are the four proposed mechanisms by which insufficient sleep may cause weight gain.
1. Too little sleep screws up your hormones
A number of experimental studies suggest that getting too little sleep can affect the signaling systems that control hunger and satiety.
More specifically, sleep deprivation has been linked to:
- reduced levels of leptin, a hormone that influences metabolism and suppresses appetite.
- increased levels of ghrelin, a peptide that stimulates hunger.
In this 2004 study, for example, sleep restriction in healthy men resulted in an average reduction of 18% in leptin and in an increase of 28% in ghrelin, as well as in increased hunger and in cravings for carbohydrate-rich foods.
Moreover, in this 2011 study published in the American Journal of Clinical Nutrition, it was found that even as little as one night of sleep loss resulted in significantly increased levels of ghrelin (11%) as well as in increased feelings of hunger in the morning.
Take-away point: research clearly shows that insufficient sleep can reduce leptin and elevate ghrelin, which regulate satiety and hunger, thereby increasing the cravings for calorie-dense, high-fat and high-carbohydrate foods.
2. Too little sleep may increase late-night snacking
The link between sleep and increased caloric intake may only partly be explained by the effects of sleep deprivation on hormones. Instead, some researchers propose that there may also be a non-hormonal (behavioral) connection between sleep and weight.
In this 2006 viewpoint article published in Obesity Reviews, it is proposed that caloric consumption is likely proportional to the number of hours that people are awake, where the longer we are awake, the more likely we are to consume more calories because of an increased opportunity to eat.
With this line of thinking, sleeping more will, theoretically, result in reduced caloric intake, especially if going to bed earlier means that less time will be spent in sedentary activities such as watching television, where snacking on high-fat, high-carbohydrate, energy-dense foods is common.
Take-away point: sleeping less may lead to increased caloric intake, since staying up later at night represents an increased opportunity to eat and is, usually, associated with television watching and snacking on calorically-dense foods.
3. Too little sleep decreases core body temperature
Body temperature is often monitored during experiments on sleep deprivation, with research reporting a significant drop in core body temperature even with just a few hours of sleep deprivation.
Such results have been seen in animal research as far as back in 1928 and have been since confirmed multiple times since then in human research, such as in this study which concluded that “sleep-deprived humans may be more vulnerable to heat loss with reduced ability to warm even at temperatures thought to be associated with thermal comfort.”
Unfortunately, very few studies have evaluated the effects of sleep loss on thermoregulation per se. This means that it is not yet entirely clear if the decrease in body temperature is a result of thermoregulatory adjustments or merely a consequence of confounding variables.
Take-away point: sleep deprivation seems to result in a drop in core body temperature, suggesting that too little sleep may impact energy expenditure through thermoregulation.
4. Too little sleep can make you less physically active
With regards to physical activity, studies have been somewhat mixed, with some research even reporting a small increase in energy expenditure during short-term sleep deprivation.
However, other research reports that individuals who are sleep deprived in experimental settings experience a reduction in Non-Exercise Activity Thermogenesis (NEAT) during the day under free-living conditions.
This makes sense, as, although energy expenditure may increase slightly with sleep deprivation, since subjects are awake for longer and, therefore, burn more calories during that time, the sleepiness and fatigue that follow could easily result in lower levels of physical activity during the day.
In fact, cross-sectional research on children has found that insufficient sleep is linked to more time spent watching television and lower levels of participation in sports.
Take-away point: short sleep durations may slightly increase energy expenditure in the short-term, since people burn more calories when they are awake than during sleep. However, the fatigue that follows chronic partial sleep deprivation seems to lead to reductions in physical activity during the day.
Sleep and weight: putting it all together
If we put together the proposed mechanisms by which sleep and weight are linked, we can see that too little sleep can affect body weight through the energy balance equation.
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