While physical activity is well known for burning calories and helping to lose weight, sleep, which is much less often mentioned, is also very important. Often associated with laziness in our modern society, it has, wrongly, a bad reputation. Many studies have linked poor (or too little) sleep to a wide range of health problems, including weight gain and obesity. One of them, published in the journal Annals of Internal Medicine, showed that those studied who slept for 8.5 hours lost 55% more body fat than those who slept for 5.5 hours. The former also reported being less hungry than the latter. A similar study had already shown that subjects who slept less than 6 hours per night had a 32% gain in visceral fat compared to 13% in those who slept 6 or 7 hours per night. This type of fat is associated with heart disease, type 2 diabetes, stroke and other chronic diseases.

Why does lack of sleep promote weight gain?

Researchers suggest that a lack of sleep affects the appetite-regulating hormones, leptin and ghrelin. It has been proven that too little sleep decreases the production of leptin, which makes you feel full, while increasing the level of ghrelin, which triggers hunger. Researchers have shown that people who slept 4 hours for two consecutive days had an 18% reduction in leptin and a 28% increase in ghrelin. A later study also noted that subjects sleeping less than 6 hours craved sugary and starchy foods more than others. Lack of sleep would also affect the body's use of glucose and fat and metabolism.

It is also important to realize how much the "internal" or circadian clock helps maintain and regulate your overall health. It's how your body anticipates environmental changes and adapts them to the right moments of the day; it's what wakes you up in the morning and makes you sleepy after dark when it's working properly. It is therefore logical that if you deprive yourself of sleep or eat when your body was planning to sleep, contradictory signals are sent to your body and lead to a disruption of the internal system.

Although no study has shown that sleep deprivation directly causes weight gain, all support a relationship between the two, as well as an increased incidence of diabetes and heart disease.

Lack of sleep certainly promotes weight gain, but it is also a precursor to many other disorders. It can weaken the immune system, decrease memory and concentration, increase the risk of diabetes, hypertension and cardiovascular disease, accelerate aging or cause or worsen depression.
That said, too much sleep is not a panacea either. Sleeping more than nine hours has also been shown to be linked to a number of health problems such as weight gain, back and headaches and heart disease.

Studies suggest that the ideal amount of sleep for most adults is seven to eight hours per night, often best learned by listening to your body.