When it comes to all things fitness and nutrition related there is often a lot of noise in the data that can lead to conflicting opinions based on the same evidence. While so many topics are interrelated, this one will simply focus on one intervention, namely light aerobic exercise timing around meals and the benefits for blood sugar control, insulin levels, and body fat. While this certainly relates to and raises questions about different exercise interventions with higher intensities, intervals, and fasted exercise, those topics will unnecessarily bloat this article and are therefore topics for further discussion elsewhere. Read on to learn how to best time low intensity continuous exercise for blood sugar control, reducing insulin secretion, improving insulin sensitivity, and shedding body fat.
Of all the confounding factors around whether or not an exercise program will be effective or not, the topic of when exercise is performed relative to eating is not likely the first to come to mind – and that’s a shame because it can make a significant difference in the outcomes realized. In fact, this single factor may be the difference between success and failure if weight loss is the primary goal of the exercise intervention (there are still all kinds of other benefits from consistent exercise that won’t be altered by this).
Key Action Items
This may seem backwards to start with highlights, but I know time is a precious commodity, so while I’ll be digging into finer details in the main article, I wanted to start right off the bat with key information you can put into action immediately. If you’re curious about more details I welcome reading on, but if you need to just grab some take-aways – here they are!
- Light aerobic exercise effectively lowers blood sugar and insulin responses when performed shortly after eating, but not before eating.
- Even ten minutes of slow cycling with no tension can make a difference.
- Bigger meals with greater glycemic loads will likely require longer exercise bouts and/or greater intensity to adequately blunt the sugar/insulin response (moderate instead of light).
- Resistance training also works, but doesn’t appear to be as effective as aerobic exercise.
- Exercise order makes a difference. Aerobics prior to resistance training is better at decreasing blood sugar response than the other way around.
- Blood sugar response is highest 30-60 minutes after eating and for best results it appears that starting exercise before that time is best if the exercise continues into that time, but not if exercise is stopped before crossing the 30-minute post meal completion mark.
- Short 10-minute bouts are likely best when completed in the 25-50 minute post-meal timeline.
- Walking a little faster may significantly alter weight loss.
- Light to moderate aerobic activity is generally safe for healthy and diabetic participants.
Let's Dig In!
As mentioned, timing of exercise appears to be a truly important factor for those seeking blood sugar control and by extension lowered insulin peaks and overall control which supports the idea that exercising for hormonal effects is going to have a more meaningful effect on weight control than simply calories in and calories out theory.
Let’s start with stating that there are numerous studies on this topic and those that have I’ve chosen are not cherry-picked to point out a preconceived result (the opposite in fact is true, I would have expected different results based on prior learning) but have been chosen as representative of the body of evidence I’ve seen in the absence of a meta-analysis or systematic review to use as a stronger source for these conclusions.
A very fascinating study was done that backed up similar trials in showing improved glucose control from walking leisurely or briskly for thirty minutes following the completion of lunch and dinner. What made this one particularly interesting to me is that it not only showed improvements in blood markers, but went into the key end-point of weight-loss as well. The biggest drawback of this study is that it fielded only two participants, the author and her assistant. However, without changing eating, but simply walking after meals the author managed to lose approximately six and a half pounds in one month walking briskly, while her assistant was able to drop over three pounds walking more leisurely. They repeated this experiment four years later and had the same results showing that the results were consistent. This may seem like a small amount of weight loss in the age of overhyped remarkable transformations, but given the time frame this is a remarkable result in the real world. What makes this even more impressive is that neither participant was overweight to begin the trial and no dietary intervention was in play.
Some key things we see in this report include noting that thirty minutes of walking was effective for blunting blood sugar response and losing weight when done immediately upon completion of eating, but not when an hour had elapsed prior to walking which was more comparable to not exercising at all for those metrics.
A systematic review of studies on exercise following eating in diabetics done in 2018 showed that in this population the best effects for sugar control were observed with longer durations of exercise (45+ minutes) at a moderate intensity. This also pooled data to show that aerobic exercise and resistance training both are supported as effective options. A newer (2021) study strengthens this finding with some noteworthy distinctions. This one pitted five different conditions against each other: control with no exercise vs aerobic exercise for 30 minutes vs aerobics for 15 minutes followed by 15 minutes of resistance training, 15 minutes of resistance training followed by 15 minutes of aerobics, and finally 15 minutes of resistance training alone. As previously found, all exercise conditions improved glucose response, but aerobics alone had the strongest effect followed closely by aerobics and resistance combined with aerobics done first. When resistance training was done first the effect wasn’t as powerful as the other way around and actually more closely aligned with doing only 15 minutes of resistance training. It would have been interesting to see an extra arm of this study where the resistance training was also performed for 30 minutes as even the 15 minutes had a marked effect, but less than 30 minutes of other combinations.
Finally, a study that I truly appreciate for seeking to find ideal timing and minimum effective dosing showed that even 10 minutes of slow cycling with no extra tension was effective at reducing blood sugar responses when completed at the 45-minute mark, but not when completed at the 15-minute mark. I appreciate this because not having time to exercise is one of the biggest barriers to increased physical activity that most people cite, so the small time commitment to get an effect is appealing. This is even more exciting to see a decent response to such low intensity exercise as that also eliminates requiring a higher baseline fitness to put it into use. I also find this one fascinating as the delayed time to start was shown to be the more effective time interval. This seems a little contradictory based on some other findings and does leave me wondering if it’s less a matter of when the exercise was done relative to the meal, but more a matter or when the sugar was tested relative to the exercise. It would be nice to see a follow up on this with other targets including the insulin response and weight loss.
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