The forgotten factor in weight control

Weight control advice has traditionally been based on the calorie principle. The idea here is that, if we want to lose weight, we need to consume fewer calories than those we burn as part of respiration and activity. This is the basis for ‘eat less, exercise more’ weight loss advice. Of these two factors, I’ve found the dietary component to be far more important. Why exercise is usually a minor factor here is perhaps a conversation for another day.

However, there is evidence that, aside from diet and exercise, another factor that plays more than a bit part in weight control is sleep. There are a number of mechanisms through which reduced sleep time might contribute to weight gain, and these were summarised in a review published in the journal Cell Biochemistry and Function back in 2012 [1].

The review, from scientists at Federal University in Sao Paulo, Brazil, refers specifically to a range of potential mechanisms here, including:

1. Reduced insulin sensitivity

One of insulin's jobs is to assist the transfer of nutrients in the bloodstream into the cells. If insulin does not do this effectively, cells can be effectively 'starved' of fuel. If, say, brain and muscle cells are under-fuelled, the end result could be mental and physical fatigue. And an under-fuelled brain would tend to predispose to heightened hunger too.

When the body is broadly resistant to insulin's effects, then the pancreas will generally pump out more insulin in an effort to lower blood sugar levels. The problem here is that insulin has a range of biochemical effects that we'd expect to translate into increased fat accumulation in the fat tissues. Here are some of insulin's key effects in this respect:

Insulin stimulates the uptake of fat into the fat cells. Insulin activates the enzyme 'lipoprotein lipase' that catalyses the conversion of fat in the form of triglycerides into smaller molecules known as fatty acids. These fatty acids, unlike triglyceride, can make their way into the fat cells.

Insulin increases the supply of glycerol for the 'fixing' of fat in the fat cell. Insulin also facilitates the uptake of sugar into cells, where it can be converted into glycerol. In combination with fatty acids, glycerol forms triglyceride again, effectively 'fixing' fat in the fat cells.

Insulin inhibits breakdown and release from fat cells. Triglyceride in the fat cells is disassembled through the action of an enzyme known as 'hormone-sensitive lipase'. Insulin inhibits this enzyme and can therefore slow fat release from the fat cells (lipolysis).

2. Raised levels of cortisol

Cortisol is a major 'stress' hormone secreted by the adrenal glands. It's essential to life, but as with everything, too much can be a bad thing. Cortisol antagonises insulin, and may therefore contribute to 'insulin resistance' (see above). It also has the ability to predispose to fat accumulation, particularly around the midriff.

3. Raised levels of ghrelin

Ghrelin is a hormone secreted by the stomach and the pancreas. It stimulates appetite through an effect on the brain. Higher levels of this hormone may drive us to overeat.

4. Lowered levels of leptin

Leptin is a hormone secreted by fat cells. It acts on the brain to quell hunger and stimulate the metabolism. Lower levels of this hormone, as induced by short sleep duration, might therefore increase hunger and put a brake on the metabolism – not ideal for someone seeking to maintain or attain a healthy weight.

5. Fatigue

Short sleep can cause us to be tired, which might contribute to obesity by reducing overall levels of activity.

The authors of this review conclude that the:

present literature highlights the importance of getting enough good sleep for metabolic health.

My feeling is this: even if lack of sleep does not pose challenges for healthy weight control (though I believe it can), it's clear that it can have adverse effects on health. Sleep's apparent ability to help us maintain a desirable weight is one of many reasons to ensure we get enough of it.

REFERENCES:

Zimberg IZ, et al. Short sleep duration and obesity: mechanisms and future perspectives. Cell Biochem Funct. 2012;30(6):524–529