Military personnel and athletes have a very high energy expenditure, which is increased during certain key periods (intense training, competition and missions). Compensating for this expenditure through adequate energy intake can be complicated by physiological ingestive limits and logistical and organizational constraints (number of meals, food availability), leading these populations to regularly find themselves in an energy deficit situation (intake below requirements). If this situation persists, it could impair physical and cognitive performance, as well as major physiological functions. Among the many constraints to which military personnel and athletes are subjected (stress, sleep deprivation, travel, etc.) that can increase the risk of energy deficiency, the impact of thermal environmental constraints is very imperfectly known. Seasonal impact and travel to countries with very different thermal environments from temperate countries can lead these populations to work in cold and hot conditions for long periods.

Understanding how exposure to hot and cold alters appetite and energy intake is therefore of the high importance. Our previous "TEMPCA" study highlighted a modulation of preferences for warm or cold foods depending on the exposure environment. By being able to adapt their food intake to these preferences, subjects were able to maintain a decent energy intake.

The primary objective of this study is to determine the effect of the temperature of the food served (hot or cold) on changes in food intake during acute exposure to hot and cold. We hypothesized that adapting the temperature of the food served according to the exposure environment (hot in a cold environment and cold in a hot environment) would enable adequate levels of energy intake.

Secondary objectives are to determine the influence of the environment on the levels of interstitial glucose during the preprandial period and to investigate the impact of thermal exposure (modulation of core temperature) on the modulation of quantities consumed and energy produced by digestion (postprandial thermogenesis). Forty participants (between 18 and 40 yo, male or female, active, lean, and healthy) will carry out 3 experimental sessions in which only the thermal environment will differ: cold condition (15°C), neutral condition (25°C) and warm condition (35°C). They will be divided into two groups, the first of which will be offered a cold meal during the three sessions (Cold Meal - CM) and the second a warm meal during the three sessions (Warm Meal - WM). They will all wear the same outfit designed to be offer perfect thermal comfort at 25 °C.

Briefly, each session will start at 8:30am after eating a standardized breakfast. Body mass and ad libitum water intake will be frequently monitored to identify possible dehydration. Thermal comfort and sensation and subjective appetite will be regularly assessed using visual analog scale.

From 11:00am to 01:00pm, all participants will be isolated and all temporal cues will be removed. At 01:00pm, an ad libitum meal (warm or cold) will be served in large quantities. The dishes will be weighed before and after the meal to assess energy intake. Before and after the meal, resting metabolism will be measured during 30 min in a supine position using indirect calorimetry and food preferences for high-fat/low-fat, savory/sweet, warm/cold foods, and fluid/solid foods will be assessed using the Leeds Food Preference Questionnaire.

Inclusion Criteria:

• Active (>3 h/w of physical activites)
• Affiliated to the social security
• Usual breakfast eaters

Exclusion Criteria:

• Unusual or irregular meal pattern
• Too high dietary restrictive profile assessed by the TFEQ-21
• Bad sleepers (< 6h/night)
• Presenting a metabolic condition
• BMI lower than 18 or higher than 30
• Chronic medication (at the exception of the contraceptive pills)
• Regular smoker (more than 2 cigarettes per day)
• Regular alcohol consumer (more then 1 glass per day)
• Vegetarian
• Following a confessional diet (hallal, casher)
• Do not speak fluently French

Active, young, lean, healthy individuals and presenting normal diet and sleep patterns.

All data and will be make available for other researchers on request.

IPD will be available when an article will be published.

Any researcher that will make a demand using e-mail address of the corresponfing author. They will have access to individual and mean data and the explanation of the gathered outcomes.