This is a dose finding study in healthy overweight to obese human volunteers (BMI 25- 35) to find the level of oral supplementation with propionate that increases plasma propionate levels to 10x the current normal plasma level and use this dose of propionate in a randomised, placebo controlled double bind study. This study will compare propionate with fermentable and non fermentable carbohydrate. The outcome measures for this study will include assessments of appetite with feeding studies, measurement of insulin sensitivity using hyperinsulinaemic euglycaemic clamps and assessment of adipose tissue distribution using MRI scans and adipose tissue biopsy to determine changes in proliferation and differentiation of adipocytes.