The purpose of this study is to determine if sleep restriction provokes an increase in risk factors for metabolic diseases, such as elevation of ectopic fat and decreased sensitivity to insulin. We propose to evaluate the effect of sleep restriction in a model of metabolic challenge (overfeeding) caricaturing the conditions of modern societies everyday life .

General hypothesis :

In overfeeding condition, the stress response generated by partial sleep restriction of six days will induce an accumulation of fat in the liver and a decreased insulin sensitivity of adipose tissue , liver and muscle, more pronounced that in overfeeding condition only, provoked by a deregulation of the nocturnal lipolysis .

Specific goals :

Purpose 1 : To measure the accumulation of fat in the liver (measured by nuclear magnetic resonance ) and the tissue insulin sensitivity ( measured by a test meal ) in response to a sleep restriction in overfeeding condition .

Hypothesis 1: In overfeeding condition (130 % of energy requirements ) , hepatic lipid accumulation will be higher after 6 days of sleep restriction (4 hours per night) compared to a control condition (8 hours of sleep per night ) . Decreased sensitivity to insulin in the liver, adipose tissue and the associated muscle will be associated at this ectopic fat accumulation.

Purpose 2 : To determine the alteration of lipolysis in response to sleep restriction in overfeeding condition.

Hypothesis 2: In overfeeding condition, sleep restriction will increase the concentrations of circulating fatty acids and glycerol in relation to condition of normal sleep.

Inclusion Criteria:

• Good general health
• BMI 18.5-25 kg/m2
• Blood pressure at rest less than 140/ 90 mmHg .
• Physical activity level: sedentary or light (< 3 hours of sport per week )
• Lack of sleep pathology ( including sleep apnea and insomnia )
• Regular sleep-wake cycles
• Average duration of sleep over 7h
• Circadian Typology by Horne & Ostberg questionnaire ≥ 30 and ≤ 70
• Score questionnaire Pittsburgh Sleep Quality Index ≤ 5
• Screening polysomnography showing sleep efficiency ≥ 85 % and apnea- hypopnea index and periodic leg movements < 15 / h .

Exclusion Criteria:

• Current smoking
• Family history of diabetes
• History of sleep disorders
• Circadian Typology by Horne & Ostberg [ 16-30 ] or [ 70-86 ]
• Score questionnaire Pittsburgh Sleep Quality Inde x> 5
• Polysomnography indicating a sleep efficiency <85% and apnea-hypopnea index and periodic leg movements > 15 / h.
• Consumption of more than 3 coffees a day
• Drinking alcool (more than 10g /d)
• Use of Drugs
• Medication
• Night work by shifts
• Average duration of sleep less than 7 hours per night
• Occupational Risks in sleep restriction conditions: e.g. professional drivers
• Special Diet ( vegetarianism, veganism , etc. )
• Change in weight of more than 3 kg in the last 3 months
• Consumption of more than 3 dl sugar-sweetened beverages per day ( sodas, energy drinks , fruit juice , flavored milk sugar )
• Contraindication for magnetic resonance imaging ( pacemaker , previous eye surgery, the presence of metal implant or foreign body, Claustrophobia, etc. )
• For women: pregnancy (current or desired)
• Hemoglobin level < 13.5g/dl for men and < 12.5g/dl for women
• Ferritin level < 50ug / l
• Blood donation in the last 8 weeks