Abstract
BackgroundInsulin-stimulated muscle blood flow facilitates plasma glucose disposal after a meal, a mechanism that is impaired in obese, insulin-resistant volunteers. Nitrate- or flavonoid-rich products, through their proposed effects on nitric oxide, may improve postprandial blood flow and, subsequently, glucose disposal. To investigate whether a single dose of nitrate-rich beetroot juice or flavonoid-rich black tea lowers postprandial muscle vascular resistance in obese volunteers and alters postprandial glucose or insulin concentrations.MethodIn a randomised, controlled, cross-over study, 16 obese, insulin-resistant males consumed 75 g glucose, which was combined with 100 ml black tea, beetroot juice or control (water). Peripheral vascular resistance (VR), calculated as mean arterial pressure divided by blood flow, was assessed in the arm and leg conduit arteries, resistance arteries and muscle microcirculation across 3 h (every 30-min) after the oral glucose load.ResultsDuring control, we found no postprandial response in VR in conduit, resistance and microvessels (all P > 0.05). Black tea decreased VR compared to control in conduit, resistance and microvessels (all P < 0.05). Beetroot juice decreased postprandial VR in resistance vessels, but not in conduit artery and microvessels. Although postprandial glucose response was similar after all interventions, postprandial insulin response was attenuated by ~29 % after tea (P < 0.0005), but not beetroot juice.ConclusionsA single dose of black tea decreased peripheral VR across upper and lower limbs after a glucose load which was accompanied by a lower insulin response. Future studies in insulin-resistant subjects are warranted to confirm the observed effects and to explore whether long-term regular tea consumption affects glucose homeostasis.Trial registrationThe study was registered at clinicaltrials.gov on 30th November 2012 (NCT01746329).Electronic supplementary materialThe online version of this article (doi:10.1186/s12986-016-0094-x) contains supplementary material, which is available to authorized users.
Highlights
Insulin-stimulated muscle blood flow facilitates plasma glucose disposal after a meal, a mechanism that is impaired in obese, insulin-resistant volunteers
During control, we found no postprandial response in vascular resistance (VR) in conduit, resistance and microvessels
Postprandial glucose response was similar after all interventions, postprandial insulin response was attenuated by ~29 % after tea (P < 0.0005), but not beetroot juice
Summary
Insulin-stimulated muscle blood flow facilitates plasma glucose disposal after a meal, a mechanism that is impaired in obese, insulin-resistant volunteers. Impaired glucose homeostasis is strongly related to the development or progression of diabetes mellitus type 2. Skeletal muscle is the principal tissue responsible for insulin-stimulated glucose disposal and significantly contributes to the postprandial regulation of glucose concentrations [2]. Studies suggest that the skeletal blood flow response is blunted to glucose or a carbohydrate-rich meal in obese individuals [4, 5]. These observations highlight the potential clinical relevance of enhancing blood flow and thereby contributing to glucose homeostasis
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