The overall goal of this study is to investigate the effects of a daily dietary supplement of brown seaweed (2 capsules of InSea2®) on body weight, glycemic control and insulin secretion in overweight prediabetic men and women in association with a moderate weight loss intervention.

Diets that produce lower glucose and insulin responses may reduce diabetes and cardiovascular risk. They may also facilitate weight control by promoting satiety, insulin sensitivity and optimal insulin secretion after a meal. Food ingredients may indeed reduce postprandial glucose and insulin response through an inhibition of α-amylase and α-glucosidase activity that may slow down the absorption of carbohydrates. InSea2® is a unique combination of polyphenolic extracts of brown algae (Ascophyllum nodosum and Fucus vesiculosus) which has been shown to inhibit the action of α-amylase and α-glucosidase. Preliminary data in healthy men and women have demonstrated a reducing effect on plasma insulin of a single intake of InSea2® consumed with a high-carbohydrate meal.

The main objective is to evaluate the effects of a daily dietary supplement of 500 mg (2 capsules) of brown algae extract powder (InSea2®) on body weight and blood glucose homeostasis (glucose, insulin, c-peptide) measured in the fasting state and during a 2-hour oral glucose tolerance test (OGTT) in overweight prediabetic men and women.

The secondary objectives are to assess the contribution of a daily consumption of this supplement (InSea2®) on weight loss when associated with a daily caloric restriction of 500 kcal due to individualized nutritional intervention on markers of lipid profile, blood pressure, inflammation, oxidative stress and gut barrier integrity.

The investigators expect that InSea2® lowers body weight and blood glucose homeostasis (glucose, insulin or C-peptide, as marker of insulin secretion, in the fasting state or during a 2-hour oral glucose tolerance test) in association with metabolic and inflammatory markers in the context of moderate weight loss in overweight prediabetic human subjects.

Inclusion Criteria:

• overweight (BMI > 25; waist circumference ≥ 80cm for women and ≥ 94 cm for men)
• fasting insulin (≥ 60 pmol/L)
• Impaired fasting glycemia with or without impaired glucose tolerance
• HbA1c between 5.6 and 6.4
• non-smoking
• stable weight in the past 3 months

Exclusion Criteria:

• diabetes
• chronic disease (thyroid dysfunction, hepatic or gastrointestinal disorder, uncontrolled hypertension)
• taking drugs that could affect glucose or lipid metabolism or weight and appetite
• taking dietary supplements (protein powders, fish oil, omega-3 or any marine supplements) or natural health products that could affect glucose, lipid, weight or appetite
• major surgery 3 months prior to the study
• pregnancy
• fish, seafood or iodine allergy