High‐glucose mixed meals impair microvascular function: the attenuating effect of exercise

Dietary habits have a major impact on human health. High-sugar food intake has been associated with increased risk of developing coronary heart disease (Huang et al. 2014). Therefore, increased intake of dietary sugars, particularly those added to processed foods or used in the preparation of foods and beverages, has become a growing worldwide health concern. Postprandial hyperglycaemia has been shown to impair macrovascular endothelial function (Loader et al. 2015). High-glucose mixed-meal ingestion has also been demonstrated to impair muscle microvascular blood flow for up to 2 h postprandially in healthy people (Parker et al. 2020a). This observation was associated with higher blood glucose and insulin levels. Evidence suggests that the most likely mechanism for these vascular impairments is the reduced bioavailability of nitric oxide as a result of its interaction with oxygen-derived species, specifically anion superoxide, which is elevated after acute hyperglycaemia (Loader et al. 2017). On the other hand, moderate exercise has been demonstrated to be an effective intervention to improve vascular function in conditions of reduced vasodilatory capacity (Hurley et al. 2019). The effect of postprandial hyperglycaemia on microvascular function has gained attention since microcirculation is critical in the control of blood flow and tissue perfusion, and microvascular dysfunction may explain the occurrence of cardiovascular disease without apparent macrovascular dysfunction. However, the majority of studies to date have focused on showing the negative impacts of a high-glucose meal on microvascular function without determining interventions to prevent dysfunction. There are now data showing that prior exercise can improve muscle microvascular blood flow and mitigate microvascular impairments induced by a high-glucose mixed-meal ingested 3 h post-exercise; moreover, this effect, was demonstrated to be present up to 24 h post-exercise, although to a lesser extent. In this issue of The Journal of Physiology, Parker and colleagues (Parker et al. 2021) add to the evidence by investigating the effects of prior exercise on muscle microvascular blood flow following a high-glucose mixed-meal ingestion at 3 h and 24 h post-exercise in eight healthy young males using a randomized crossover design. The participants performed a single bout of moderate graded cycling exercise test until volitional exhaustion and used three experimental conditions: (1) a meal with no prior exercise, (2) a meal 3 h after exercise and (3) a meal 24 h after exercise. Microvascular blood flow of the vastus lateralis muscle was measured by real-time contrast enhanced ultrasound at 0 min (pre-meal), and at 60 and 120 min postprandially. They reported that muscle microvascular blood flow decreased at 60 min and 120 min following high-glucose mixed-meal ingestion compared to the pre-meal timepoint, irrespective of the experimental condition. More importantly, however, the study demonstrates that compared to the control condition (without exercise), muscle microvascular blood flow was elevated by ∼74% in the 3 h post-exercise condition prior to ingesting the meal, indicating the lasting effects of acute exercise on muscle microvascular blood flow. Furthermore, this elevation in microvascular blood flow persisted throughout the high-glucose postprandial period at 60 min (∼112%), and 120 min (∼223%) postprandially, and was also elevated at 120 min postprandially in the 24 h post-exercise condition (∼132%). This effect was accompanied by increased postprandial glycaemia and delayed insulin responses. Therefore, despite the fact that high-glucose meal ingestion reduces muscle microvascular blood flow, prior moderate-intensity cycling exercise improves it to values above those observed when no prior exercise was performed. However, some limitations of the study should be pointed out. Firstly, only male volunteers were included, making it difficult to know whether similar effects would have been observed in females as well. Secondly, the participants in the current study were self-reported to be untrained but recreationally active, with levels of weekly physical activity ranging from low to high. Microvascular function may vary based on training status, and therefore, results cannot necessarily be extrapolated to all training levels. Notwithstanding these limitations, this study adds to the growing body of evidence about the benefits of moderate intensity exercise for protecting microvascular function from the negative implications of habitual consumption of high-sugar foods on cardiovascular health. Furthermore, the data highlight the importance of exercise in the control and prevention of microvascular dysfunction induced by acute hyperglycaemia, and raise awareness of the importance of preventing cardiovascular diseases and/or other health problems, such as diabetes and obesity, by combining regular exercise and healthy eating habits. The author declares no competing interests in relation to this article. Sole author. No funding sources supported the preparation of this article.