The prevalence of Type II Diabetes (T2D) continues to rise globally, and particularly in Western nations (1).  Without proper treatment, T2D may lead to cardiovascular diseases, neuropathy, kidney failure, and death (2).

Authors: Gabriel Zieff, B.S., Andrew Borror, B.A., Claudio Battaglini, Ph.D., FACSM, Lee Stoner Ph.D., ACSM-CEP, ACSM-EIM

Department of Exercise and Sport Science, University of North Carolina at Chapel Hill

BACKGROUND

The prevalence of Type II Diabetes (T2D) continues to rise globally, and particularly in Western nations (1).  Without proper treatment, T2D may lead to cardiovascular diseases, neuropathy, kidney failure, and death (2).

The major goal of T2D treatment is the regulation of hyperglycemia (high blood sugar). Lifestyle behaviors such as eating a healthy diet and engaging in exercise can be effective strategies for mitigating hyperglycemia and improving insulin sensitivity in T2D (3, 5). In terms of exercise, muscle-contraction-mediated glucose uptake provides a means for glucose to exit the bloodstream and enter the muscle tissue independent of insulin. Specifically, repeated muscular contractions stimulate transient translocation of the GLUT-4 transporter protein to the cell-membrane to facilitate the uptake of glucose from the circulation into the muscle.

Given the importance of managing hyperglycemia in T2D, it is not surprising that glucose elevation following meals is of particular concern for this population. Thus, postprandial exercise may be a useful strategy to combat the glycemic response to a meal while preserving insulin sensitivity. Unfortunately, the optimal timing and prescription of postprandial exercise to maximally reduce postprandial hyperglycemia have not been clearly elucidated.

Recently, a systematic review was conducted to assess the effects of postprandial exercise on glucose regulation in T2D (6). This article: i) reports the outcomes of the systematic review; ii) discusses the appropriate timing, modality, intensity, and duration of exercise; and iii) addresses the practical considerations that need to be accounted for when prescribing and monitoring exercise in this population.

SYSTEMATIC REVIEW FINDINGS

The systematic review identified 12 randomized crossover trials, with a total of 135 participants (108 males, 20 females, 7 unknown), none of whom were being treated with insulin. The crossover trials included an acute exercise bout, and a non-exercise control. The exercise bouts were performed within a three-hour period following a standardized meal.

The analysis revealed that postprandial aerobic exercise (11 studies) decreased short-term glucose area under the curve (AUC) by 3.4% to 26.6% and 24-hour prevalence of hyperglycemia by 11.9% to 65% (6). Resistance training (2 studies) decreased short-term glucose AUC by 30% and 24-hour prevalence of hyperglycemia by 35% (6–8). Further, the review showed that while pre-prandial exercise also conferred beneficial effects on glucose regulation, greater improvements occurred with postprandial exercise (6-10). It is likely that when postprandial exercise is performed, maximal exercise-induced glycemic regulation is most aligned with peak blood glucose (11). In contrast, pre-prandial exercise may not allow for such coordination between exercise-induced glycemic regulation and blood glucose elevation.

Unfortunately, as far as we know, no studies have examined whether the attenuation of postprandial glucose improves clinical outcomes, such as cardiovascular events. However, the evidence from the review suggests that postprandial exercise decreases blood glucose levels to below 8.6 mmol/L for up to 24 hours, which approximately corresponds to a glycated hemoglobin (HbA_1C) level of 7% (8–10, 12–14). Chronic decreases in HbA_1C to this extent are associated with a reduced risk of cardiovascular death, non-fatal myocardial infarction, and non-fatal stroke (12). While the findings from the systematic review should be considered preliminary, the 24-hour reduction in blood glucose is potentially clinically meaningful.

APPROPRIATE TIMING, INTENSITY AND MODALITY OF EXERCISE PRESCRIPTION

Timing and Intensity: Longer duration (30 to 60 minutes), moderate-intensity, aerobic exercise in the 3-hour period following a meal seems to most consistently result in improved glucose regulation among individuals with T2D (6). Lower intensities and shorter durations of exercise were not as effective in promoting glucose regulation (6). A likely explanation is that a driving factor behind the glucoregulatory effects of postprandial exercise is total energy expenditure.

Modality: While less evidence exists regarding the glucose improvement related to postprandial resistance training, the available evidence does suggest resistance training and moderate-intensity aerobic exercise are similarly effective (6).

CONSIDERATIONS FOR EXERCISE PRESCRIPTION

The American College of Sports Medicine (ACSM) recommends accumulating 150 minutes of moderate intensity or 60 minutes of vigorous intensity aerobic exercise per week. It also recommends performing 2 to 3 non-consecutive days of resistance training per week at intensities between 50% to 80% of 1-repetition maximum (1-RM) and targeting all major muscle groups using a scheme of 1 to 4 sets of 8 to 15 repetitions per exercise. We recommend that the current ACSM guidelines, which are similar to those provided by the American Diabetes Association (ADA), be adhered to. However, we suggest that exercise be performed within three hours of the largest meal of the day. We also suggest that several other minor modifications to these guidelines be considered, as discussed below.

With regards to ACSM guidelines, the findings of the systematic review lead to several important considerations. First, while the ACSM recommendations for aerobic exercise are stated in terms of cumulative minutes of exercise achieved per week, due to the transient (≈ 18 to 48 hours) nature of contraction-mediated glucose uptake, we suggest that no more than two days should occur without engaging in aerobic exercise (15). In line with this we suggest that, between aerobic and resistance exercises, only one “rest-day” be taken each week. In terms of resistance training, we suggest that a moderate-intensity range of 50% to 60% 1-RM be maintained to prevent large increases in blood pressure and minimize delayed-onset muscle soreness. These recommendations will help to optimize safety and compliance. Lastly, clinicians should aim to help individuals with T2D work up to a duration of 60 minutes of exercise (regardless of aerobic or resistance) at least 6 days per week to maximize energy expenditure.

It is important to note that these guidelines are ideals and rigid adherence to them may be unrealistic. Therefore, the most important underlying themes of lifestyle-based glycemic regulation should be prioritized. In particular, strategies for relapse prevention should be prioritized. For example, if the prescribed exercise following the largest meal cannot be achieved for a given day, engagement in any form of physical activity, such as taking the dog for a walk or gardening, should be encouraged.

CONCLUSION

Postprandial hyperglycemia is a significant problem for individuals with T2D. The current evidence indicates that postprandial exercise may help reduce hyperglycemia, thus preventing the progression of T2D and associated complications. Although the optimal intensity and timing of initiation are not clear, energy expenditure seems to be an important factor.

Based on this, we suggest that clinicians and fitness professionals help individuals with T2D adhere to the current ACSM and ADA guidelines. However, we suggest that a greater emphasis be placed on meeting these recommendations during the three-hour period following the largest meal of the day.

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