According to the American College of Sports Medicine’s flagship journal, Medicine and Science in Sports and Exercise (1), there are more than 21 million Americans with Type 2 Diabetes as of 2010 with an estimated 7 million undiagnosed. If these numbers don’t mean much, let’s give it some perspective: in 1958 there were only 1.5 million. (Granted, the US population has increased, but only from about 180 million to 310 million, not 15-fold as in the numbers of T2D.) Furthermore, due to the now-defined pre-diabetes – or sub-clinical diabetes where the precursors to diabetes are lurking if lifestyle does not change dramatically – it is estimated that 80 million Americans are at risk. Thus, some public health officials are predicting that 21-33% of Americans will have diabetes by the year 2050. The healthcare burden this portends will bankrupt the nation. To make matters worse, the preponderance of both pre-diabetes and T2D is increasing in children and adolescents as sedentary behavior, poor diet and obesity abounds.
While prevention is optimal and much is being done in the way of public health messaging, one of the best means by which to regulate blood sugar in either healthy, pre-diabetes or T2D patients is through physical exercise. Recall above where we discussed how muscles use the sugar in the blood for fuel. The more muscles you have and the more regularly they work at some critical level of effort, the easier it is to control blood sugar. In fact, one’s levels of physical activity (PA) may be a better predictor of risk for diabetes than one’s BMI (body mass index, a ratio of height to weight.)
For the sake of discussion, we should break down physical activity into three main types – activities of daily living (ADL), aerobic exercise (AE) and resistance (or strength) exercise (RE). The MSSE article reviewed the data on all these for their impact on blood sugar, insulin control and T2D risk. Not unremarkably, the evidence strongly suggests that the more active you are, the lower your post-meal and long-term blood sugar is, the better your muscles are able to use the sugar in the blood (glucose tolerance or insulin sensitivity), the lower or lesser your insulin response is to food intake, and the lower your risk for diabetes is. What is remarkable, however, is how little physical activity is required in order to affect many of these changes and benefits.
As far as ADLs is concerned, the general prescription is to ambulate (walk, run, bike, etc) for 30-60 minutes a day or close to 10,000 steps/day, or almost 4 miles/day. This does not mean you have to take walks that last that long; it means you should move around more often throughout the day and sit less often. In fact, some studies show that simply standing up for 2 minute bouts of walking every 20 minutes of sitting lowered post-meal blood sugar and insulin response to eating. (2) While walking is effective, new studies (3) demonstrate that high intensity interval training (HIIT), or sprinting, may be an even better regulator of blood sugar. Comparing training programs in two groups of sedentary women, one doing intervals of moderate intensity, the other at high intensity, the authors found that the HIIT group had slightly greater fat oxidation in the muscles, a roundabout indicator of improved glucose control. HIIT might also be more time efficient.
Between the two studies referenced here, and many more that have looked at HIIT programs compared to traditional long, slower/lower intensity programs, the general belief is that the more muscles that are contracting and the harder they contract, the better the short-term and long-term blood sugar control. The only caveat here is that large muscle groups or bigger body movements are necessary to see these effects; single joint/small muscle contractions will not elicit the disease-modifying effects one might be seeking. For these reasons, RT has been getting more looks when it comes to modifying risk factors for T2D. In fact, the preponderance of evidence shows that RT, at sufficiently high enough intensities to build muscle mass, improves blood sugar control both by using sugar to fuel contractions and by improving the insulin sensitivity of those muscles even after the workouts.
Overall, physical activity has been shown to be an effective, efficient and low-risk/low side-effects treatment and preventive for T2D. A single bout of exercise is sufficient to regulate blood sugar for the next 16-24 hours.
As such, it is recommended that exercise be partaken nearly every day for at least 30 minutes; if obesity is a factor in a patient’s disease, then 60-90 minutes of accumulated physical activity is strongly suggested. Furthermore, a combination exercise prescription of cardiovascular and RT exercise – either same or alternating days – is deemed optimal.
To conclude, physical activity of all sorts has been found to enhance blood sugar uptake by muscles during the session and for several hours thereafter. Thus, it is one of the best, least invasive means by which to prevent, regulate and, for early stage T2D, even reverse diabetes and its downstream effects on the heart, kidneys, nerves (especially of the lower extremities), and eyes. Besides its collateral benefits on the cardiovascular system, it may help reduce weight though it is essential in maintaining weight loss. And PA clearly improves quality of life, not just through its physical benefits but its effects on the brain and psyche, reducing the risk of depression which may be a factor in both the sequence of events leading to weight gain, the challenges of both weight loss and disease management, and the reduction in one’s ability to enjoy various aspects of life due to immobility, neuropathy, visual impairment, and dialysis.
For more information about diabetes, exercise, pharmaceutical management and research, please visit the American Diabetes Association site at diabetes.org
Dr. Irv Rubenstein graduated Vanderbilt-Peabody in 1988 with a PhD in exercise science, having already co-founded STEPS Fitness, Inc. two years earlier — Tennessee’s first personal fitness training center. One of his goals was to foster the evolution of the then-fledgling field of personal training into a viable and mature profession, and has done so over the past 3 decades, teaching trainers across through country. As a writer and speaker, Dr. Irv has earned a national reputation as one who can answer the hard questions about exercise and fitness – not just the “how” but the “why”.
References
1. Roberts et al, Modification of Insulin Sensitivity and Glycemic Control by Activity and Exercise. MSSE, Vol. 2013: 45(10):1868-1877
2. Dunstan et al., Breaking up prolonged sitting reduces glucose and insulin responses. Diabetes Care, 2012:35(5): 976-983
3. Astorino et al., Effect of Two Doses of Interval Training on Maximal Fat Oxidation in Sedentary Women. MSSE, Vol. 45(10), pp.1878-1886, 2013
