In humans, prolonged alterations in the circadian rhythm have been linked to cognitive impairments, premature ageing, and oncological and metabolic disorders such as diabetes and obesity. Obesity, in particular, is an ever-increasing condition with innumerable deleterious effects on human health. In recent years, studies have shown a relationship between a person's chronotype (morning or evening) and eating habits, as well as the importance of adapting these habits to physiological rhythms. Furthermore, it has been suggested that customising the caloric distribution of meals according to personal circadian rhythms may influence body weight and be one of the strategies to control overweight and obesity. In spite of the strong interest in this topic and the increasing number of observational studies conducted, there is currently a lack of intervention studies evaluating whether a low-calorie diet that takes into account the individual chronotype may be more effective than a standard low-calorie diet in the treatment of overweight and/or obesity.

Background

Society has changed enormously in recent decades and this has had a strong impact on the processes regulating circadian rhythms, in particular the sleep-wake and fasting-eating cycles. The 'normalisation' of the environment, favoured by technological progress, has in fact caused light pollution, noise pollution, excessive thermoregulation, continuous work shifts and disordered eating, leading to an uncoordinated circadian cycle with consequences on physical and mental balance. In humans, prolonged alterations of the biological clock have been linked to cognitive disorders, premature ageing, and oncological and metabolic diseases such as diabetes and obesity. Obesity, in particular, is a condition with innumerable negative effects on human health.

In recent years, a new branch of nutritional research has aroused growing interest in the scientific community: this is chrono-nutrition, which combines elements of nutritional research with elements of chronobiology and studies the impact of eating times on health. The first to use the term "chrono-dystrophy" as a chronic desynchronisation of circadian rhythms were Erren and colleagues, who in their work reported how a loss of synchronisation between environmental signals and physiological processes can lead to alterations in the communication between the central nervous system and peripheral clocks and a change in the subject's metabolism. Subsequently, numerous studies have evaluated the impact of the thirteen dimensions of eating behaviour - timing, frequency and regularity - on health, hypothesising a possible role of the individual circadian rhythm, or chronotype, on the risk of developing overweight and/or obesity. Recent data have demonstrated a relationship between a person's chronotype (morning or evening) and eating habits, as well as the importance of adapting these habits to physiological rhythms. Furthermore, it has been suggested that customising the caloric distribution of meals according to personal circadian rhythms may influence body weight and be one of the strategies to control overweight and obesity. Indeed, recent research has shown that calories ingested at different times of the day have different effects on energy utilisation, leading to differential weight loss, even in the presence of isocaloric quantities.

Despite the strong interest in this topic and the increasing number of observational studies conducted, there is currently a lack of intervention studies evaluating whether a dietary regimen can be used to control body weight. Evidence to date suggests that in order to increase the effectiveness of low-calorie diets, it may be of great interest to consider not only patients' daily energy expenditure but also their circadian preferences. Overall, chrono-nutrition could mediate the effects between sleep, diet and urbanisation, but further research is needed to elucidate the precise physiological and metabolic mechanisms underlying this phenomenon, the importance of chronotype for metabolic health and its impact on public health.

Objectives of the study

The objectives of the study are to compare the effects of a diet with a daily calorie distribution adapted to the individual chronotype with a control diet with a conventional daily calorie distribution. The primary outcome is weight change from baseline. Secondary outcomes are changes in body mass index (BMI), percentage of fat mass, biochemical parameters and gut microbiota profile.

Inclusion Criteria:

• overweight or obese condition (BMI≥25 kg/m2)
• age between 18 and 65 years
• willing to give informes consent

Exclusion Criteria:

• chronic illnesses or unstable conditions (e.g. cancer, kidney or liver disease, inflammatory-intestinal disease, cognitive decline, psychiatric disease)
• drug therapies (use of corticosteroids, antidiabetic drugs)
• pregnancy or intention to become pregnant in the next 12 months
• breastfeeding
• current or recent (last 3 months) adoption of a low-calorie diet

In this trial blinding of experimenters will not be possible as they will have to administer the chronotype diet in the intervention group