Exercise and blood sugar

There is no doubt that exercise yields benefits across a spectrum of health: reduced blood pressure,  reduced inflammation, reduced blood coagulation, better weight control, stronger bones, less depression, reduced risk for heart attack.

Exercise also influences blood sugar. Diabetics understand this best: Exercise reduces blood sugar 20, 30, 50 or more milligrams. A starting blood sugar, for instance, of 160 mg/dl can be reduced to 80 mg/dl by jogging or riding a bicycle. (I recently had brunch at an Indian restaurant with my family. Blood sugar one-hour postprandial: 134 mg/dl. I was sleepy and foggy. I got on my stationary bike and pedalled at a moderate clip for 60 minutes. Blood sugar: 90 mg/dl.)

Could the reduction of blood sugar with exercise be THE reason that exercise and physical activity provide such substantial benefits?

Think about it. Reduced blood sugar:

1) Reduces risk for future cardiovascular events.
2) Reduces glycation of proteins, i.e., reduced glucose binding to proteins like the ones in artery walls and the lenses of your eyes.
3) Reduces blood coagulation
4) Reduces endothelial dysfunction (abnormal artery constriction that leads to atherosclerosis)

This might explain why it doesn't require high levels of aerobic activity to derive benefit from exercise, since even modest efforts (e.g., a 15-minute walk after eating) reduce blood sugar substantially.

The incredible 33-year, 18,000-participant Whitehall study tells us that a postprandial (after-eating) blood sugar of an impossibly-difficult 83 mg/dl is required to erase the excess cardiovascular risk of blood sugar. Could this simply be telling us that physical activity or exercise is required to suppress blood sugars to these low levels?

It makes me wonder if an index of the adequacy of exercise is your post-exercise blood glucose.

Comments (30) -

  • Pythonic Avocado

    3/5/2010 2:02:20 PM |

    You don't say it, but imply, that if you had not exercised, your blood sugar would have been higher than if you had not exercised. My question is how much higher? How much of the reduction is due to the exercise and how much is just normal blood sugar lowering over time? Thanks!

  • Gretchen

    3/5/2010 2:08:58 PM |

    One caveat. If you have diabetes, you may see your blood glucose levels go *up* right after strenuous exercise. This is because the body sees that as stressful, and the stress hormones cause insulin resistance.

    This is especially true if you start exercising when the BG levels are relatively low, say in the 80s. My BGs can go up to 140 if I'm moving heavy furniture or pushing a heavy mower up a steep hill. I once saw a post by a high-powered cyclist who measured the BG of his fellow racers after a race and found that they also went up to about 140. But then they came down quickly. His stayed high.

    However, later, the BG levels should go down as the body refills glycogen stores that have been deplete.

  • Anonymous

    3/5/2010 6:01:42 PM |

    I'm wondering if fasting blood sugars play a role here.  My experience confirms what you pointed out in an earlier post:  if I wake up with blood sugar of 85, then for example a banana won't take me that high 30 mins later. But if I wake up at 98, then with a banana first thing in the morning I'll hit 140 in 30 minutes, before it goes down.

    What I can't explain is why some days I wake up at 85 and other days at 98.  Could exercise be the reason? If so, then maybe the timing of exercise -- whether it's after a meal or not -- is less important than whether it happens and brings down fasting glucose, which in turn brings down Post-prandial glucose.  

    Just thinking aloud.

  • Kent

    3/5/2010 6:14:35 PM |

    If one can reduce their blood sugar down to an acceptable level of say 80-90 mg/dl by exercising after indulging in something like banannas, would this be an acceptable way of enjoying a favorite treat without negative consequinces?


  • Mole

    3/5/2010 6:19:57 PM |

    Great insight.

  • Anonymous

    3/5/2010 6:33:23 PM |

    Dr. Davis,

    Thanks for another thought provoking post.  BTW, what glucose meter do you use?


  • Anonymous

    3/5/2010 7:26:17 PM |

    When I had GD, and religiously tracked my post-prandial blood sugars, one of the highest readings I had came after I took some exercise between the end of the meal and the one hour reading.  The exercise was in the form of about 15 minutes on the mini-trampoline.  Perhaps the form of exercise makes a difference, I don't know.  I never tried that experiment again (didn't want the hopelessly conventional nurse I was required to report to to yell at me).

  • Laura

    3/5/2010 7:26:17 PM |

    I decided to test this out.  For breakfast this morning, I had roast beef in tomatoes.  My postprandial blood glucose(1 hr) was 114 (11:02 am).  After a short, moderate walk, my blood was 85 (11:22 am).


  • Jolly

    3/5/2010 8:53:31 PM |

    Does exercise *always* reduce blood sugar, or does it instead regulate blood sugar.  Richard at Free The Animal states that exercise increases his blood sugar when he is in a fasting state.  


  • shel

    3/5/2010 9:18:31 PM |

    from personal experience, i completely agree with this post.

    from everything i've read and studied, worrying about macronutrient ratios is pointless in the context of a whole food diet (my bias toward paleo) when we get adequate exercise.

    perhaps, instead of sweating about our intake of apples and tubers and sitting on our butts, we should sweat a bit and take a brisk evening walk and lift some weights.

  • King

    3/5/2010 10:30:37 PM |

    Dr.  Davis,
    This post further reinforces my view that "insulin resistance" is a nature body reaction to how much fuel (glycogen/glucose) is in the muscles and liver (if they are full, no more room) as much as other often mentioned factors.  When the muscles are full there is no place for the blood sugar to go except into fat cells under the influence of elevated insulin.  With exercise the fuel supply in the muscle is reduced so that there is room for more fuel.  This would seem to be what happened in your case.  If this is the case then the amount of muscle one uses during exercise would have a most profound effect on the blood sugar level (i.e. jogging good, weight training better).  
    Maybe your "index of the adequacy of exercise" could be used to finally provide a better objective method to rate exercise methods (instead of oxygen uptake, etc.).  This would allow for comparisons of the intensity, duration and other variables that are constantly thrown around when discussing aerobic vs. anaerobic, long distance vs. intervals, etc. (might adversely affect infomercial exercise equipment sales however)   Could it be that the height of the blood sugar spike isn't as important as the duration and the duration of the spike can be significantly reduced if exercise is part of the lifestyle and properly timed.  Also, maybe this measure could be used to better define how exercise and eating cycles should be structures for optimum health, weight loss, etc.  Are there other health indicating measurements that might benefit from this same sort of post-meal/exercise analysis?  Maybe it’s been done and I haven't stumbled across (or did and it didn't stick).  Very thought provoking post.  Thanks.

  • Sifter

    3/5/2010 10:36:11 PM |

    Interesting, but what about anaroebic exercise, i.e. weight lifting fairly heavy for moderate reps, for instance? Studies always cite 'exercise' when it is really not one monolothic activity. Could clean and pressing a 50 lb dumbbell for x time give you the same blood glucose benefit of your 15 minute walk?....

  • Drs. Cynthia and David

    3/6/2010 9:22:12 AM |

    I'm not sure it's that simple, and maybe it depends on whether you're starting fed or empty (with higher glucose levels or from baseline).  I've measured post exercise blood sugars and they're usually higher than when I started- like today, started at 95 and went to 128 after a slow 4.5 mile jog.  I interpret that as the normal action of epinephrine and glucagon to produce glucose from liver glycogen during exercise, but I was surprised to see it that high when I was intentionally keeping the intensity down.  After 45 min rest, it had come down to 101. I don't know what would happen if I had started with a high blood glucose though (I usually don't eat much before running).

    Thanks for your stimulating ideas and discussion.


  • Dr. William Davis

    3/6/2010 1:49:33 PM |

    The effects of physical activity on blood sugar are, indeed, more complex than a simple exercise, blood sugar goes down.

    However, in the specific situation of light exercise in the immediate postprandial period, there is, as a rule, a marked reduction in blood glucose.

    Had I not exercise, my blood glucose would have more than likely stayed around the 130-140 range for a couple of hours, given the mix of foods I consumed.

  • www

    3/7/2010 3:28:39 AM |

    Dr Davis,

    If you want to keep blood glucose level low would it make sense to work out before we eat a fixed amount of food or to eat after a work out?


  • Anonymous

    3/9/2010 2:45:05 PM |

    In my experience a glass or two of wine with a meal has the result of reducing post prandial blood glucose levels - presumably it inhibits the liver's production of sugar whilst it is busy removing the alcohol out of the blood stream.  Don't take my word for it - use your meter and note the difference it makes.

    Now as to whether that's a good thing or not?  Might go a little way to explaining why moderate alcohol consumption appears to have some health benefits.

    Paul Anderson

  • Anonymous

    3/9/2010 4:03:17 PM |

    I am in good shape, lean, and generally have postprandial BG less than a 100 eating the right breafast, lunch and dinner for me.

    A good hard aerobic 45 min workout spikes me to 120 area and slowly comes down - something my meals don't do!

    I wonder if I should time this differently?

  • Orlando personal injury lawyer

    3/9/2010 8:18:10 PM |

    Thanks a lot for this explanation. I enjoyed reading this article.

  • Anonymous

    3/9/2010 9:12:45 PM |

    Hmm that's amazing but frankly i have a hard time figuring it... Sure, I see the point, but it's still abit challenging... wonder how others think about this..

  • Anonymous

    3/9/2010 9:27:13 PM |

    Well... that's very interessting but to be honest i have a hard time seeing it...  wonder what others have to say..

  • automated external defibrillator

    3/21/2010 7:48:09 AM |

    Thanks for sharing such a useful article. From personal experience i agree with you.
    Beside all you said there's something in my mind.. Isn't yoga good for blood sugar patients?

  • Anonymous

    3/28/2010 6:17:44 PM |

    For those with significant IR, your intraday, between-meal BG is mainly governed by gluconeogenesis - the formation of glucose from amino acids released by continued protein digestion.  A bout of exercise will only briefly reduce your BG to fasting levels, after which it will climb back again to higher levels due to continued protein digestion.

    So exercise can't be used in any simply way to "fix" high post-meal BGs.  Rather, it's benefit comes mainly from building more muscle mass, which then results in generally lower BGs.

  • EMR

    5/12/2010 5:33:37 AM |

    Exercise is very useful and good for the body and general health.This with a well balanced diet is a perfect solution towards good health.

  • christina

    9/8/2010 7:13:07 AM |

    I am really thankful to the author of this post for making this lovely and informative article live here for us. We really appreciate your effort. Keep up the good work. . . .


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    11/3/2010 2:32:23 PM |

    Exercise also influences blood sugar. Diabetics understand this best: Exercise reduces blood sugar 20, 30, 50 or more milligrams. A starting blood sugar, for instance, of 160 mg/dl can be reduced to 80 mg/dl by jogging or riding a bicycle. (I recently had brunch at an Indian restaurant with my family. Blood sugar one-hour postprandial: 134 mg/dl. I was sleepy and foggy. I got on my stationary bike and pedalled at a moderate clip for 60 minutes. Blood sugar: 90 mg/dl.)

  • Daniel A. Clinton, RN, BSN

    1/23/2011 4:32:16 AM |

    Jolly's post interests me. I suspect she's right. I'm sure the body moves blood sugar levels to a desirable range when under physiologic stress, be it higher or lower. Just for most Americans, that means lower.

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    1/31/2011 6:06:48 PM |

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  • J

    7/5/2011 6:26:19 PM |

    I was actually searching the web to see if I was really weird or not. (still not sure) When I exercise i often see a dramatic spike in my blood sugar. Yesterday after a 4 mile run I was 260ish and have tested into the 160's-200 on several occasions after exercising....is this as bizarre as it seems? I'm young (in my 20s), healthy, and not-diabetic.