Exercise, the Healthiest Snack! Study Shows More Than 10% Reduction in 3h Post-Prandial Blood Glucose Levels W/ Intense Exercise (Cardio + Weights) Before Each Meal

That's how your healthy "exercise snack" could look like - just make sure your boss knows that you're doing it to make sure you stay healthy and don't miss a day at the office ;-)

Do you think about having a Snickers® bar right now? Why don't you go and work out instead? Sounds crazy? I know, but a recent study from the School of Physical Education at the faculty for Sport and Exercise Sciences of the University of Otago says: "Dosing exercise as brief, intense ‘exercise snacks’ before main meals is a time-efficient and effective approach to improve glycaemic control in individuals with insulin resistance." (Francois. 2014)

Now the obvious questions are (1) what exactly is a "brief, intense exercise snack" and (2) what can you expect from having it before a meal?

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To answer these questions we have to take a closer look at the experimental protocol the scientists used. In order to investigate whether three small doses of intense exercise before meals (aka ‘exercise snacking’) would result in better postprandial blood glucose control than a single bout of (energy-matched) prolonged, continuous, moderate-intensity exercise in individuals with insulin resistance, Francois et al. had their, 16 volunteers who met the inclusion criteria of being aged 18–55 years and not being medicated for blood glucose or high blood pressure participate in all of the following experimental conditions:

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  Traditional continuous exercise (CONT) -- Participants com pleted one 30 min bout of treadmill walking at a moderate intensity (60% HRmax) 30 min before their evening meal (dinner) in accordance with current physical activity guide lines (WHO. 2010). Every 5 min, HR (Polar S810i; Polar Electro, Kempele, Finland) was measured, a rating of perceived exer tion (RPE, using the BORG 6-20 scale) was made and the work rate was adjusted accordingly.
• Exercise snacking (ES) -- Six 1 min work bouts, consisting of walking at 90% HRmaxwith 1 min recovery (slow walk) between each, were completed 30 min before breakfast, lunch and dinner. The total energy cost for CONT and ES were matched (based on metabolic calculations inV˙O2max test). The exercise was undertaken on an incline treadmill, with HR and RPE measured at the end of each interval.
• Composite exercise snacking (CES) -- Six 1 min work bouts alternating between walking and resistance-based exercise were performed, with 1 min recovery between each bout, 30 min before breakfast, lunch and dinner. The total number of 1 min work bouts balanced the ES regime. The resistance based exercise bouts were undertaken using resistance bands (as many reps as possible within 60 s), and walking was at 90% HRmax on an incline treadmill, with HR and RPE measured at the end of each interval. The resistance-band exercises worked the musculature of the arms, back and core. All exercise sessions included a 5min warm-up period and a 3 min cool-down period at a self-selected intensity on a treadmill.

To ensure an equal playing ground for all three types of "snacks", the timing of the three meals was identical between the three exercise trials.

Table 1: Total daily macronutrient intake for the participants’first experimental trial (Francois. 2014)

"For their first trial, participants consumed their habitual diet under free-living conditions while completing a 5-day dietary log. The diet was then replicated for the second and third trials, so that timing, composition and quantity of all food and drink consumed were matched between the three trials. Subsequent dietary analysis (Kai-culator Enhanced 2010 Food Composition Database v0.43; Dunedin, New Zealand) for the main days of interest is shown in Table 1. Physical activity levels for the three trials were monitored using pedometers and activity logs." (Francois. 2014)

As you can see in Figure 1, the exercise snacking protocols lowered the mean postprandial glucose (PPG) following breakfast (by 1.0±0.9 mmol/l [mean ±SD]) and dinner (by 0.5±0.8 mmol/l) but not following lunch (−0.0±0.7 mmol/l). Previous studies with somewhat more intense regimen showed improvement irrespective of the time of the day (Devlin. 1985), though. If you don't stick to running 1.2k, but hop on a treadmill for 3-5 sets of 1 min all out running or a tabata style workout, you should see improvements on every meal.

Figure 1: The 3 h PPG AUC for breakfast (a), lunch (b) and dinner (c) on the exercise day for CONT, ES and CES trials. Data are means ± SD,n=9. *p<0.05 for ES vs CONT for breakfast and dinner PPG AUC (Francois. 2014)

The interaction between meal and exercise was, as the scientists point out, quadratic-by-time (p=0.05), with the highest PPG concentration, and reduction with exercise, observed in the morning and evening, and the lowest after lunch. In contrast, CONT had no effect on 3 h mean PPG at any time point (bearing in mind that CONT also served as a control condition for breakfast PPG and lunch PPG on the exercise day).

Figure 2: Over the whole 24h the reduction in blood glucose was most pronounced in the "composite" exer- cise snacking trial, where the subjects performed a combination of aerobic and resistance exercise ~30 min be- fore their three meals (Francois. 2014)

Bottom line: If you snack, you better do it intensely. Intensely as in "heavy", not as in "super sweet". So forget about the initially mentioned snickers or whatever other dietary snack may have been on your mind. Grab some resistance bands and get out and run to the next best green area to show the slackers why you're lean and fit and not fat and sick ;-)

Before you get all fired up for the idea of "exercise snacking", I would yet like to remind you that it may not be feasible before each and every of your meals. So, be careful not to obsess about being able to eat only after a mini-workout, ah... exercise snack. Why? Well, it's a pretty short way from dedication to obsession and "having to work out before every meal" is a first and huge step towards an eating disorder that will make your life more miserable, but not of healthier | Comment on Facebook.

References:

• Devlin, J. T., and E. S. Horton. "Effects of prior high-intensity exercise on glucose metabolism in normal and insulin-resistant men." Diabetes 34.10 (1985): 973-979.
• Francois, Monique E., et al. "‘Exercise snacks’ before meals: a novel strategy to improve glycaemic control in individuals with insulin resistance." Diabetologia (2014): 1-9.
• World Health Organization. "Global recommendations on physical activity for health." (2010).