Diabesity 2016; 2 (1): 1- 11 doi: 10.15562/diabesity.2016.21 www.diabesity.ejournals.ca REVIEW Hyperinsulinemia: Best management practice Catherine A.P Crofts*1, Caryn Zinn1, Mark C Wheldon2, Grant M Schofield1 ABSTRACT Chronic hyperinsulinemia associated with insulin resistance is directly and indirectly associated with many metabolic disorders that contribute to significant morbidity and mortality. Because hyperinsulinemia is not widely recognised as an independent health risk, there are few studies that assess management strategies. Medication management may not address the multiple issues associated with hyperinsulinemia. Lifestyle management includes physical activity, especially high intensity interval training, and dietary management. Reducing carbohydrate quantity and increasing nutrient density are discussed with carbohydrate-restricted and Mediterranean diets conferring additional benefits to a low-fat diet. Physical activity and dietary management provide the foundation for hyperinsulinemia management and may work synergistically. Of these principles, a combination of resistance and high intensity interval training, and carbohydrate restriction provide the two most effective frontline management strategies for managing hyperinsulinemia. Keywords: Hyperinsulinemia, hyperglycemia, type 2 diabetes, insulin resistance, secretagogue, syndrome x symptomatic improvement of conditions associated Introduction with hyperinsulinemia such as polycystic ovarian Compensatory hyperinsulinemia (further syndrome (PCOS). referred to as "hyperinsulinemia") is associated, There are two main strategies for managing mechanistically and epidemiologically, with many hyperinsulinemia: maximising insulin sensitivity and chronic metabolic diseases.1, 2 The aetiology of reducing glycemic load. Insulin sensitivity can be hyperinsulinemia is likely heterogeneous2 and in the maximised via up-regulating GLUT4 or insulin earliest stages asymptomatic.3 Early management of receptors, or by preventing (further) insulin resistance. hyperinsulinemia may prevent, delay, or mitigate the Glycemic load may occur through two main pathways, severity of subsequent pathologies. Although endogenous through metabolic pathways such as hyperinsulinemia is a common co-pathology with gluconeogenesis, glycolysis, or renal reabsorption4, and impaired glycemic control, this paper focuses on the exogenous via dietary intake. management of hyperinsulinemia in the presence of There are three main mechanisms to achieve normal glucose tolerance. each of these strategies: Physical activity, diet, and There are several different states that depict medicines and other supplements. the continuum that reflects healthy insulin response through to hyperinsulinemia. It is proposed that Methodology people transition between different states, which may Literature was reviewed on hyperinsulinemia be either acute or chronic, depending on the and insulin resistance, targeting full-text English circumstances at the time, and may be subject to language studies. There was no date criterion. Articles change. The close relationship between the two were selected on the basis of having a minimum of different states of hyperinsulinemia and insulin both a plausible biological mechanism and established resistance can also be noted. This means that as well as clinical association. An academic database search targeting insulin levels directly, strategies that improve included EBSCO, Medline and Google Scholar, using insulin sensitivity, especially the up-regulation of variants of the terms “hyperinsulinemia,” “insulin glucose transporter type 4 (GLUT4), will also reduce resistance,” “type 2 diabetes,” and “metabolic hyperinsulinemia. As there are few studies that directly syndrome,” and each of these terms in conjunction assess hyperinsulinemia management strategies, this with variants of “diet,” “nutrition,” “physical activity,” review will include strategies that improve glycemic “pharmacology,” and “treatment.” References were control in the absence of evidence of increased insulin based on the authors’ judgment of relevance, secretion. It will also consider strategies that provide Corresponding Author, E-mail: [email protected]. 1Human Potential Centre & 2Biostatistics and Epidemiology, Auckland University of Technology (AUT), PO Box 92006, Auckland 1142, New Zealand. Copyright: © 2015 The Authors. This is an open-access article distributed under the terms of the Creative Commons Attribution License. Hyperinsulinemia: Best management practice … Catherine Crofts et al. completeness, and compatibility with clinical, other studies comparing aerobic to resistance training, epidemiological, pathological and biochemical criteria. which only showed improvements in glucose disposal when the results were expressed per kilo of fat-free- Physical activity mass. Physical activity is well-documented for While resistance training is believed to improving insulin sensitivity. Mechanistically this enhance cellular metabolic capacity by mechanisms occurs via GLUT4 up-regulation, increased such as GLUT4 mobilization9, potentially negative hexokinase gene transcription5, increased fuel effects by way of increased cortisol are also observed. consumption and, if sustained, decreases to insulin Crucially, fewer repetitions and longer rest periods secretion.6 Conversely, sustained physical activity can between sets elicit a lower cortisol response, which also increase glucagon, cortisol and catecholamine may be important for beginners to resistance secretion.6 These hormones can all increase training.10 Increased catecholamine and/or insulin gluconeogenesis and if unbalanced, impair rather than secretion may also be observed with resistance improve insulin sensitivity. Very intense physical training. These changes may also be exercise-dose activity stimulates insulin production, especially in the dependent and may attenuate as training adaptation presence of hyperglycemia. Without question, physical occurs. An elevated insulin response is associated with activity will be a key component for managing protein/carbohydrate supplementation. Elevated hyperinsulinemia, but the question remains whether hormonal responses may also be associated with different forms of physical activity can maximize overtraining.10 sensitivity while minimizing counter-hormones. Physical activity can be broadly divided into Aerobic exercise two main classifications that have considerable Aerobic exercise can be broadly described as overlap: resistance training and aerobic activity. The light to moderate intensity activities that can be latter has a further subset: high intensity interval performed for extended periods of time. Examples of training (HIIT). aerobic exercise include walking, jogging and swimming. There is a large body of literature on the Resistance training type and amount of aerobic activity required to Resistance training is characterized by muscles maintain health. Conventional wisdom suggests that a contracting against an external resistance causing brief minimum of 30 accumulated minutes of moderate and isolated activity of single muscle groups.7 The intensity activity (ie. brisk walking) should occur on health-benefits of resistance training are well- most days to achieve health benefits11, although the recognized. These can include decreases to HbA1c, efficacy of this volume has since been questioned.12 weight, body fat, and blood pressure.8 Other Aerobic exercise is believed to improve metabolic improvements include increases to bone mineral health via the same mechanisms as resistance training. density, and lean body mass. There are also potential A meta-analysis comparing resistance training benefits to mood and cognition, balance and falls-risk, to aerobic exercise concluded that clinically, there were and overall self-esteem. no advantages between resistance training and aerobic Resistance training may improve exercise for lowering HbA1c or impacting hyperinsulinemia through three main mechanisms: cardiovascular risk.7 However, aerobic exercise was increasing, or maintaining muscle mass, glucose modestly advantageous for lowering BMI. Resistance expenditure and enhancing the cellular metabolic training may confer greater benefit to those with capacity. It is estimated that inactive adults lose 3-8% limited mobility as many of the exercises can be of muscle mass per decade accompanied by a performed by the sedentary. reduction in resting metabolic rate8 Losing muscle mass means that glucose disposal will be harder High intensity interval training (HIIT) resulting in increased adiposity. Increased muscle mass HIIT protocols are a subset of aerobic is posited as one explanation for the improvements in exercise characterized by short, maximal-intensity, glucose disposal rates for resistance training.9 This is anaerobic exercise sessions separated by medium or because both weight lifters and long-distance runners low intensity periods for recovery. There are several show increased glucose disposal rates compared to advantages to HIIT protocols compared to controls; however, this difference remains only for the conventional aerobic exercise: time; glucose utilization long-distance runners after differences in lean-body- and cellular metabolic capacity. Lack of time is the mass are taken into account. This is consistent with biggest reason cited for not exercising.9 HIIT protocols allow for greater power output for an Diabesity 2016; 2 (1): 1-11. doi: 10.15562/diabesity.2016.21 www.diabesity.ejournals.ca 2 Hyperinsulinemia: