Obesity is an epidemic in Western society and is the biggest risk factor for insulin resistance and type 2 diabetes. The investigators have recently shown that exposure to hyperbaric oxygen (HBO) leads to an increase insulin sensitivity in males ubjects and that this improvement can be measured in all men, not just those with diabetes. The aim of this study is to investigate the time course of this effect and explore the mechanisms involved. The investigators suspect that insulin sensitivity as measured by hyperinsulinaemic-euglycaemic clamp will be increased within the time-frame of one 2-hour hyperbaric oxygen exposure, and that the improvement will be measurable in females as well as males.

Inclusion Criteria:

• Overweight to obese (BMI 25-35 kg/m2)
• Age >18 years (no specific upper age limit)
• Fit to enter hyperbaric chamber as assessed by hyperbaric physician.

Exclusion Criteria:

• Personal history of Diabetes
• Personal history of major psychiatric disorders
• UIse of prescribed or non-prescribed medications which may affect glucose homeostasis (e.g. steroids),
• Uncontrolled asthma,
• Current fever or upper respiratory infections
• Individuals who regularly perform high intensity exercise (>2 week),
• Pregnancy, lactation and women who are planning to become pregnant
• Current intake of >140g alcohol/week,
• Current smokers of cigarettes/cigars/marijuana,
• Current inatke of any illicit substance,
• Claustrophobia
• has donated blood within past 3 months.