Applied nutritional investigationGlycemic response to carbohydrate and the effects of exercise and protein
Introduction
Type 2 diabetes mellitus (T2DM) is a largely preventable lifestyle disease, yet remains extremely prevalent in our society. Controlling blood glucose levels is important in the prevention and management of T2DM, as chronic hyperglycemia may increase the risk for insulin resistance and T2DM, and is the main cause of diabetes-associated complications [1], [2]. Carbohydrate-containing foods have a large influence on blood glucose levels, which have been a focal point of significant research [3], [4], [5], [6].
It has been suggested that the overall glycemic index (GI) and glycemic load (GL) of the diet are independently related to the risk for developing T2DM [7], [8]. Studies have found that low GI or GL diets may result in reduced insulin release, improved glycemic control, and increased insulin sensitivity, and ultimately might help prevent T2DM; whereas high intakes of high GI and GL carbohydrates over short-term and long-term periods may produce greater insulin resistance and increase the risk for developing T2DM [7], [8], [9]. Understanding ways to control the glycemic response to carbohydrate is important in preventing T2DM and reducing the risk for complications associated with existing diabetes.
The glycemic response to carbohydrate is typically thought to be dependent on the amount and type of carbohydrate consumed [10]. However, many other factors also might influence the glycemic response, including age, sex, metabolism, exercise status, and coingestion of other macronutrients [11], [12], [13].
Exercise also might play a large role in mediating the glycemic and insulinemic responses to carbohydrates [14]. Long-term exercise training over periods of at least 12 wk has been shown to improve insulin sensitivity and reduce glycemic response [11], [13], [15], [16], [17]. However, there is some discrepancy in the literature regarding the acute effects of exercise on postprandial glycemic response. Some studies have reported impairment in glucose tolerance immediately after aerobic exercise [17], [18], [19], whereas others have observed improvements [11], [20]. The use of different exercise intensities, modes (e.g., aerobic versus resistance), durations, timing of exercise relative to feeding and methods of testing glucose tolerance (e.g., oral glucose tolerance test, frequently sampled intravenous glucose tolerance test) within these studies may be the cause of these inconsistent findings.
Another possible mechanism for reducing the glycemic response to a carbohydrate is the coingestion of protein [21]. The addition of between 5 g and 50 g of protein to a carbohydrate load has been shown to reduce the area under the blood glucose curve in both healthy and diabetic patients in a dose-dependent manner [21], [22], [23]. The proposed mechanisms by which protein mediates these effects on blood glucose are either by stimulating insulin release, and/or the presence of protein in the gut, which may slow the digestion and absorption of carbohydrates [3], [24], [25]. It is believed that the amino acid profile of proteins also might affect the insulinemic response [26], [27].
The simple combination of lifestyle and dietary strategies (adding protein to a carbohydrate meal after exercise) has the potential to significantly lower the postprandial glycemic response. The magnitude and potential interaction of these effects have not been compared within the same group of individuals. A more thorough understanding of these interactions might enable more specific and appropriate lifestyle recommendations targeted at reduced glycemic responses to possibly assist in the prevention of T2DM. This study aims to investigate the individual and combined effects of prior aerobic exercise and protein coingestion on the glycemic and insulinemic responses to carbohydrates in healthy individuals.
Section snippets
Design
The study was a randomized crossover design in which all 21 volunteers participated in four trials. These included 1) glucose ingestion at rest (RG), 2) glucose and protein ingestion at rest (RGP), 3) glucose ingestion after moderate intensity exercise (EG), and 4) glucose and protein ingestion after moderate intensity exercise (EGP). Each trial was conducted at least 5 d apart. After arriving at the laboratory in the fasted state, participants exercised or sat comfortably, then consumed a test
Results
There was no significant effect of sex on any parameters (P > 0.05). Therefore, data from both men and women are presented together (N = 21).
Discussion
This study investigated the individual and combined effects of prior exercise and protein ingestion on blood glucose and insulin responses to a carbohydrate load. The main finding was that glucose, when ingested with protein, produced a lower glycemic response than when ingested alone. However, a single prior bout of aerobic exercise did not seem to have any significant effect on the subsequent glycemic or insulinemic response to a carbohydrate. Furthermore, exercise did not appear to influence
Conclusion
The addition of protein to a glucose load significantly altered glycemic and insulinemic responses, and this effect was not moderated by changes associated with a single bout of aerobic exercise. Practically, this suggests that adding protein to a meal containing carbohydrate may reduce postprandial glycemic responses irrespective of preceding exercise.
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Shelley Roberts: Conception and design of study, generation, collection, assembly, analysis and interpretation of data, drafting or revision of manuscript, approval of final version of manuscript.
Ben Desbrow: Conception and design of study, generation, collection, assembly, analysis and interpretation of data, drafting or revision of manuscript, approval of final version of manuscript.
Gary Grant: Analysis and interpretation of data, drafting or revision of manuscript, approval of final version of manuscript.
Shailendra Anoopkumar-Dukie: Analysis and interpretation of data, drafting or revision of manuscript, approval of final version of manuscript.
Dr Michael Leveritt: Conception and design of study, generation, collection, assembly, analysis and interpretation of data, drafting or revision of manuscript, approval of final version of manuscript.
Griffith University provided material support. This research received no funding.