To date, the optimal timing for pasta consumption remains uncertain. Based on recent evidence in the field of chrono-nutrition, it is speculated that eating pasta at dinner may have a negative impact on cardio-metabolic health. Carbohydrate intake during a period of minimal glucose tolerance could potentially alter the glycaemic profile and increase the risk of overweight and obesity. Conversely, other studies indicate that consuming carbohydrates at dinner may enhance sleep efficiency and quality. Thus, the aim of this study is, for the first time, to evaluate whether there are discernible differences between consuming pasta at lunch or dinner for the human health.

Background:

Pasta plays an indisputable role in the Mediterranean diet pyramid. Indeed, it is an excellent source of carbohydrates that can be part of a varied, balanced, and healthy diet. Despite this, more and more people are avoiding it because they consider it too caloric and associate it with weight gain, especially if eaten in the evening.

While it is known with certainty that the consumption of pasta, in the right quantities, is associated with positive health effects, there is limited information on the optimal time to consume it. The most common hypothesis is that it is better to consume it at lunch, as metabolism undergoes a physiological and progressive reduction as the evening approaches. Furthermore, recent findings in the field of chrono-nutrition have highlighted that glucose tolerance is high during the day and minimal during the night, suggesting that consuming a high amount of carbohydrates in the evening may predispose to weight gain and a worsened cardio-metabolic profile. On the other hand, according to some studies, consuming carbohydrates in the evening may ensure good sleep quality, as they are an excellent source of tryptophan, an amino acid that promotes serotonin production, also known as the sleep hormone.

Recently, some studies on animal models have suggested that the timing of carbohydrate consumption could also impact the composition and functionality of the gut microbiota. For example, it has been observed that the production of short-chain fatty acids (SCFA) fluctuates throughout the day under the control of the host's circadian rhythms. Considering that SCFA are produced from carbohydrates and are fundamental regulators for many metabolic processes, it could be extremely interesting to explore the relationship between "when carbohydrates are consumed" and microbial functionality.

In conclusion, to date, studies that have evaluated the timing of carbohydrate consumption are limited and rely on physiological and chrono-biological assumptions rather than experimental evidence. Consequently, it is not known whether consuming pasta at lunch or dinner, in the right quantities, may have effects on human weight and health.

Objective of the study:

The aim of this study is to assess, for the first time, whether there is a difference between consuming pasta at lunch or dinner in terms of sleep quality, anthropometric parameters, cardiovascular risk factors, composition and functionality of the gut microbiota in a sample of normal-weight subjects. Additionally, individual chronotype will be taken into consideration, a construct indicating when a subject is most active during the day, as recent studies have highlighted its impact on dietary habits, especially in terms of "meal timing," and human health.

Inclusion Criteria:

• normal weight condition (BMI=18.5-24.9 kg/m2)
• age between 18 and 65 years
• willing to give informed consent

Exclusion Criteria:

• subjects who were involved in night work, planned long-distance jet travel during the study period, had irregular sleeping schedules or were taking any drugs known to affect sleep or metabolism
• presence of current chronic illness or unstable condition (e.g., cardiovascular disease, chronic liver disease, inflammatory bowel disease)
• current or recent (past 2 months) use of antibiotics or probiotics
• pregnancy or intention to become pregnant in the next 12 months
• breastfeeding

In this study it will not be possible to blind the experimenters and participants. Blinding will be impossible for the experimenters, as they will provide the food plan with the dietary intervention. Blinding will also not be possible for the participants, who will have to eat pasta only at dinner for 3 months and only at lunch for the same period of time.