Effect of 6-week Strawberry Supplementation on Insulin Action (STR2)

This study is a single-center, randomized and single blinded, placebo-controlled, 6-week, parallel design study with follow-up to evaluate strawberry-associated chronic improvements in insulin action resulting in reduced whole body insulin resistance and improved glucose tolerance. This study will take approximately 11~12 weeks.

Subjects will follow an extremely limited polyphenolic diet throughout the duration of their participation in the study.

The limited diet will begin 7 days before the first study visit and end before the last study visit. Following the polyphenol-free 7-day run in period, at Week 0, subjects will be scheduled to return to the Center for sequence randomization, an Oral Glucose Tolerance Test (OGTT) as well as a Flow Mediated Dilation (FMD) procedure to measure endothelial function. Subjects will incorporate either one of tow Placebo Beverages (PBO1, n=15; PBO2, n=15) or Strawberry Beverage (STR, n=15, an optimal strawberry test dose of 40 g/d) into their diet daily for a period of 6 weeks. Subjects will consume randomly assigned beverage twice per day with their breakfast and dinner meals.

All subjects will be asked to come to the Center once a week where they will receive a week's supply of beverages. Additionally, fasting clinical and laboratory variables, anthropometrics, and vital sign measurements will be assessed at each bi-weekly visit at Week 3 and Week 5.

Participants will undergo the same procedures at the end of Week 6: fasting blood sample collection for analysis of insulin, glucose, oxidative and inflammatory markers, an OGTT to assess glucose handling, as well as a FMD procedure to assess endothelial function in response to 6 weeks of either the Placebo or Strawberry treatment.

Subjects will be required to visit the Center 4 weeks after the end of their intervention period (Week 10), at which time they will undergo their last anthropometrics and vital sign measurements, a 4 hour OGTT, and the FMD procedure.

Inclusion criteria

• Must meet ONE or MORE of the criteria (1)-(5) associated with insulin resistance along with all other criteria listed (6)-(9):

• Blood glucose concentration between140-199 mg/dL at 2hr from OGTT.
• Elevated fasting glucose (110 mg/dL≤ Fasting blood glucose <126 mg/dL)
• Elevated fasting insulin (>75th percentile cutoff of 13.13 μU/mL)
• Insulin resistance defined by the homeostasis model assessment method of insulin resistance (HOMA-IR) (glucose [in millimoles per liter] × insulin [in microunits per milliliter]/22.5) values of at least 2.5.
• Waist circumference ≥ 110 cm because many epidemiology studies have been shown that waist circumferences may be related to insulin resistance.
• Nonsmokers
• Not taking any medications that would interfere with outcomes of the study, i.e. lipid lowering medications, anti-inflammatory drugs, or dietary supplements
• 18 years of age and older
• No clinical evidence of cardiovascular, metabolic, respiratory, renal, gastrointestinal or hepatic disease

Exclusion criteria

• Pregnant and/or lactating.

• Allergy or intolerance to strawberries and dairy products.
• Current regular consumption of strawberries is > 2 servings per day.
• Fasting blood glucose ≥ 126 mg/dL. Subjects identified with elevated fasting blood glucose levels will be advised to contact their primary care physician for appropriate follow-up care.
• Taking over the counter antioxidant supplements or other supplements that may interfere with the study procedures or endpoints.
• Subjects with unusual dietary habits (e.g. pica).
• Actively losing weight or trying to lose weight (unstable body weight fluctuations of > 5 kg in a 60 day period).
• Excessive exercisers or trained athletes.
• Subjects with documented atherosclerotic disease, inflammatory disease, diabetes mellitus, or other systemic diseases.
• Addicted to drugs and/or alcohol.
• Medically documented psychiatric or neurological disturbances.
• Smoker (past smoker may be allowed if cessation is > 2 years).