The term 'chronobiology' comes from the Greek 'kronos' (time), 'bios' (life) and 'logos' (study). It is the science that studies the circadian rhythms (from the Latin circa diem, meaning approximately one day).
During the 24 hours of a day, your body passes through different phases of hormonal secretion, physical coordination and sleep. Depending on the time of day, your hormones metabolise certain nutrients better, and that is very interesting in terms of the success of diets.
In mammals, there is a biological clock in the hypothalamus which is synchronised with the stimuli of light and darkness. There are also clocks in peripheral tissues which can be modulated by the central clock and by food.
In the morning, the central clock alarm sounds and cortisone, the waking-up hormone, is activated; it travels through the blood to set the time schedule for tissues and organs.
In the afternoon, the body temperature rises slightly and then drops at night. This is a sign for the body clock to prepare itself for rest.
The adipose tissue shows a circadian rhythm. Its clock genes are able to regulate the rhythmic expression of the hormones which determine appetite and weight, such as adiponectin, leptin and resistin.
The degree of DNA methylation of these clock genes increases with obesity and if you eat quickly or snack between meals. These genes do not express themselves well and that also produces sleep alterations and a greater accumulation of fat around the waist. The good thing is that this methylation is reversible if you change your eating habits and you can lose kilos until you reach a healthy weight.
Chronodisruption is an alteration of the circadian rhythms which favour obesity and diabetes. It occurs frequently with age, jet lag, shift work, when you sleep with a light on or without closing the curtains, when you take your mobile phone or tablet to bed, or when you eat without taking into account hormonal rhythms.
How to take advantage of chronobiology
If for a time you stop snacking between meals, don't eat when you're bored and eat a bit more slowly, you will 'demethylate' the clock gene, which will help you to become slimmer, sleep better and be healthier.
First thing in the morning it is essential to eat foods which increase the production of tyrosine, because thisenables us to be more active physically and also intellectually. The foods which can help with this are dried fruits and nuts, cereals, fish and pulses. It is best to eat carbohydrates at lunchtime (bread, pasta, rice, potatoes) and have protein with a vegetable garnish in the evening.
If you eat your main meal of the day after 3pm, you will find it harder to lose weight. According to a study published in the International Journal of Obesity, 420 overweight people followed a Mediterranean diet for 20 weeks (they ate the same, rested the same, took the same exercise, but half of them ate their main meal of the day before 3pm) and those who ate later only lost an average of eight kilos, while the others lost 12.
Eating an evening meal after 9.30pm favours chronodisruption. Working shifts or at night alters the circadian rythms of the appetite hormones (leptin and ghrelin) and increases total calorie consumption.
Ghrelin gives a feeling of hunger and peaks three times: 8am, 12 noon and 8pm, which is why the daily meals should be eaten around these times, when the pancreas and liver are more active.