In the modern era, food access is widely available and it is not uncommon for the time between breakfast and a late night snack to exceed 14 hours. The investigators are interested in studying whether limiting this window to 8 hours will have any beneficial effects of human health as has been demonstrated in animal models. Eight men were asked to restrict their energy intake window to between 8 am and 4 pm for two weeks whilst maintaining their habitual diet (quantity and composition). Improvements in skeletal muscle and whole-body insulin sensitivity were observed but these were potentially confounded by an average weight loss of 1 kg. Therefore an additional control group was recruited to follow a daily caloric deficit of ~400 kilocalories without changing the timing of intake.

All participants were monitored for a one week baseline period to establish their habitual physical activity and dietary patterns. This was done using food diaries, interstitial glucose monitors and a combined heart rate + accelerometer device. Participants consumed a standardised evening meal ~12h before visiting the laboratory to assess their metabolic response to a liquid test meal (1g/kg bodyweight dextrose and 0.4g/kg bodyweight protein) using the arterio-venous forearm balance model. Dual-energy X-ray absorptiometry scans, indirect calorimetry measurements and fasted and postprandial vastus lateralis biopsies were also obtained.

From the next day, participants either restricted their daily energy intake window to between 8 am and 4 pm or were prescribed a caloric deficit diet (~400 kilocalories/day) for two weeks. Physical activity, interstitial glucose concentrations and dietary patterns were monitored throughout. After this, participants visited the laboratory again to assess changes in metabolism and body composition.

Inclusion Criteria:

• Healthy male between 18 and 35 years old
• Body mass index between 18 and 27.5 kg.m^-2
• Regular breakfast consumer, 5 or more days per week
• Moderate physical activity level (PAL between 1.6 and 2)

Exclusion Criteria:

• Smoking
• Any metabolic (e.g. diabetes), endocrine (e.g. hyperthyroidism) or cardiovascular (heart or blood) abnormalities including hypertension.
• Clinically significant abnormalities on screening including ECG abnormalities
• Routine medication that may alter cardiovascular function and blood flow (e.g. blood pressure-lowering drugs or drugs that cause hypertension)
• High alcohol consumption (Routinely >4 units per day)
• Eating attitudes test (EAT-26) score > 20
• On an energy-restricted diet
• Significant body mass fluctuation in previous 3 months (>5%)