Eating in natural light helps with weight loss

Take note if you've come back from holiday with a few extra pounds. Science has shown that if you adjust your meals to the daylight and most active times of the day and eat food in a certain order when you sit down at the table - vegetables, fruit, protein and, lastly, carbohydrates - you can avoid accumulating fat, facilitate weight loss and prevent cardiovascular disease. These good habits are taught to us by 'chrononutrition', an emerging discipline that studies the close relationship between metabolism and the circadian clock - physical and mental changes that follow a 24-hour cycle and respond mainly to light and darkness.

"Chrononutrition takes into account the timing, frequency and regularity of intakes," say UPV/EHU researchers Iker Gómez García, Alfredo Fernández-Quintela, Jenifer Trepiana and María Puy Portillo, authors of a study that provides the keys to how health is affected by when and in what order we eat. In their study, they conclude that "restricting food intake to the hours of the day when it is light is an interesting strategy for maintaining a correct metabolic state and promoting weight loss."

Many of the physiological processes that occur in our body are conditioned by this 'circadian system'. For example, when the sun rises, the synthesis of cortisol - the wakefulness hormone - shoots up, while the synthesis of melatonin - the sleep hormone - reaches its minimum. And at night the opposite process takes place. "The production of these two hormones manages to control, without us realising it, everything from the regulation of body temperature to the balance of blood glucose concentrations," say the researchers.

But many environmental factors affect the relationship between circadian rhythms and metabolism, including artificial light, stress, shift work and jet lag when travelling. These are known as "chronodisruptors". "They contribute to the development of chronic diseases such as obesity and diabetes," they say. Following unhealthy diets, not keeping regular mealtimes, skipping meals and eating late at night leads to the disruption of circadian rhythms and, in turn, to a higher prevalence of obesity in the population. It also increases the risk of diabetes and cardiovascular disease.

"Several studies have already shown that staying awake and eating at times physiologically intended for sleep jeopardises an optimal metabolic state," they say. Not only that, but unusual eating times have been linked to alterations in the amount of energy expended throughout the day - we burn less for the same effort - changes in glucose metabolism and even disturbances in eating behaviour, as it affects appetite-stimulating hormones.

We should therefore restrict our food intake to specific time slots: to the times of the day when we are most active. This is an effective way to avoid weight gain. This habit would also "increase glucose tolerance and reduce insulin resistance".

In practice, this means eating most of the day's food at breakfast, mid-morning break and at lunch. As the evening progresses, try to keep meals as light as possible. "There is scientific evidence that eating most of the daily calories and carbohydrate-rich foods at lunchtime and in the early afternoon, avoiding a late dinner, facilitates greater energy expenditure throughout the day and is essential for the correct synchronisation of circadian clocks," they say.

On the other hand, prioritising the consumption of some food groups over others at the same meal can help us to control our weight. "Eating fibre-rich foods (vegetables and fruit) first, followed by protein foods (such as meat and fish) and leaving carbohydrates (cereals, bread, etc.) for last, could reduce post-meal sugar spikes and lower blood glucose levels. It also helps to prevent the development of diabetes."