Strawberries Improve Insulin Resistance and Related Cardiometabolic Markers in Adults with Prediabetes: A Randomized Controlled Crossover Trial

Abstract

Background: Prediabetes, as a risk factor for type 2 diabetes, as well as cardiovascular disease, is a burgeoning public health concern in the United States and worldwide. Dietary supplementation of polyphenol-rich berries has been demonstrated to be a feasible nutritional intervention in improving multiple cardiometabolic risk factors in adults. However, reported clinical trials are quite heterogeneous in study findings, and focus on prediabetes is lacking.

Objectives: We examined the effects of a feasible dietary dose of strawberries (32 g freeze-dried strawberries ∼2.5 servings fresh strawberries) on glycemic control (primary) and cardiometabolic markers in adults with prediabetes in a 28-wk randomized controlled (no strawberry) crossover single-blinded study (12 wk/period).

Methods: A total of 25 adults were recruited in each period of the study, and anthropometric, clinical, and dietary data and blood samples were collected at baseline, 6 wk, 12 wk, 16 wk (washout), 22 wk, and 28 wk of the crossover study. A mixed-model analysis of variance was used to examine treatment effects accounting for the fixed effects of treatment, time, order of randomization, age, sex, ethnicity, body mass index (in kg/m²), dietary calories, and physical activity over time, as well as the baseline value for each outcome.

Results: Strawberry period significantly improved glycemic control (serum insulin, insulin resistance, fasting glucose and glycated hemoglobin) and serum total cholesterol in an adjusted model compared with control; [adjusted mean difference 95% confidence interval (CI): -6.9 μIU/mL (-3.2, -10.7) μIU/mL, -2.3 (-1.3, -3.4), -8.9 mg/dL (-4.7, -13.2) mg/dL, and -0.2% (-0.1, -0.3)%, and -7.0 mg/dL (-2.0, -12.0) mg/dL, respectively, all P < 0.05]. Strawberry period also decreased body weight, high sensitivity C-reactive protein, and interleukin-6 in the adjusted model (all P < 0.05).

Conclusions: These findings show that a 2.5-serving dose of strawberries consumed daily for 12 wk can improve prediabetes status and overall cardiometabolic profile in adults.

Keywords: glycemic control; inflammation; insulin; prediabetes; strawberry.