Unique benefits of resistance exercise to BG level management and the importance of a low glycemic index post-exercise meal
by Adam Burrack, PhD
Today we return to practical matters of blood glucose level management with exercise for the individual with type 1 diabetes (T1D). While YOUglycemia’s primary athletic pursuits are aerobic sports, there are many and various benefits to be gleaned from resistance training (eg, weight lifting). Importantly these benefits from resistance training accumulate whether one trains for and competes in aerobic sports or not. The general benefits from resistance training fall into two broad categories: (1) metabolic and (2) structural. For people with diabetes, the primary metabolic benefit of resistance training is enhanced insulin sensitivity – due to improved muscle mass and resting metabolism – both immediately following resistance training (acute) and over time, as resistance training continues (chronic). The “structural” benefits of resistance training include improved muscle tone, improved posture, and ideally improved bone density. For best long-term health results, a combination of aerobic exercise and resistance training tend to yield the best results in fitness and performance – for both competitive athletes and non-competitive athletes.
To highlight recent research in this area we’ll take a look at work performed by Dr. Jane Yardley, currently on the faculty at the University of Alberta. In a 2012 paper published in the journal Diabetes Care, Dr Yardley and colleagues studied the effect of order of exercise modality in a combined 90-minute exercise session. Participants performed 45 minutes of both resistance (3 sets of 10 lifts, 7 different exercises) and aerobic (60% of VO2 max for 45 minutes) exercise. The clear result from this study was better stability of BG levels throughout the 90-minutes – and the following hour – if resistance exercise was performed first. When aerobic exercise was performed first, participants both “crashed” more severely during aerobic exercise and “rebounded” more severely during resistance exercise and the subsequent hour. In a related 2013 manuscript, Dr. Yardley separated resistance and aerobic exercise to separate days and tracked BG levels for 12 hours post-exercise. This study demonstrated less of a “spike” upwards in BG level following resistance training than following aerobic exercise. Dr Yardley and colleagues speculate that this lack of a “spike” in BG levels following resistance exercise may partially explain benefits to HbA1c levels described from longer-term resistance training, which has been suggested by other researchers. Taken together, these two studies demonstrate that resistance training promotes less acute changes in BG level than aerobic exercise in people with diabetes. One question that comes to mind is the fitness level of study participants, and whether these results would hold for well-conditioned aerobic athletes such as veteran marathon runners or elite-amateur cyclists.
In an exciting recent development, Dr. Yardley and colleagues have initiated a clinical trial in Canada to specifically study the benefits of resistance training in people with T1D who already perform aerobic exercise, similar to the question I raise above. We at YOUglycemia look forward to results of the READI study!
Now that we understand better how to avoid large BG level swings during aerobic exercise – moderate resistance training prior to our aerobic workout appears to blunt the BG level “crash” which can occur early during aerobic exercise – let’s take a look at how our food choices in the meal following an exercise session influence our overnight BG levels.
In a 2014 manuscript in Diabetes Care, Matthew Campbell at Northumbria University in Newcastle and collaborators studied the effect of the glycemic index of the meal following evening aerobic exercise on overnight BG levels and levels of acute inflammation. Glycemic index (GI) is a bit of a controversial subject in nutritional science: suffice to say that GI is a scale of 0-100 which estimates how quickly the sugar in a particular food item is broken down and released into the circulation. The general idea with GI is that the higher the number, the more quickly sugar gets into the circulation – causing a spike in blood sugar levels – and consequently a spike in insulin levels (for people with a functioning endocrine pancreas who can produce their own insulin). As one might imagine, it is standard advice from nutritionists to council most folks to avoid foods on the higher end of the GI scale. In the setting of a person with T1D exercising, this is particularly relevant: enhanced post-exercise insulin sensitivity combined with a large bolus of injected insulin for high-GI foods could be seen as a recipe for disaster – an overnight low BG episode following hard aerobic exercise. And indeed, this is the type of pattern that Dr. Campbell’s group observed in their 2014 study: a higher-GI post-exercise meal correlated with more severe post-exercise hyperglycemia and higher levels of inflammation. Importantly, inflammation can promote insulin resistance separately from effects of GI level of food. This leads to a straight-forward conclusion: best to avoid this mess and eat a relatively low-GI following evening aerobic exercise.
These two strings of research have two straight-forward lessons. First, as an athlete with T1D, resistance exercise is your friend – it can blunt some of the BG level swings associated with aerobic exercise – if performed prior to aerobic exercise. Second, if your schedule is such that you have to late evening aerobic workouts and cannot lift weights beforehand, best to avoid high-GI foods in the immediate post-exercise meal.