How many carb grams do you use to cover a 15 minute bike trip?

How far down does 15 minutes of exercise on a bike take your blood sugar? I’d like to get an idea since I was talking with another type 1 today and bouncing was going on big time. How do you best cover the bike hikes without the glucose hitting downwards too far too fast? Take 15 grams ahead? 5 grams ahead before starting out and another 5-10 about 15 minutes later? Is there another place on this web site where I can find out? Thanks to all.

Dear Leona.

Thats a hard one to answer since it depends how much glucose you liver spews out when it is told by the hormones that you are under stress and yes exercise is stress. In my case the BG would actually go up. So in the begining when not using insulin I made a rule to bike a minimum of 1 hour to make sure that it went down.

If your liver does not spew out any glucose. Then assuming the bicycling is somewhat strenous it would burn about 10 calories a minute or 150 calories. If you take 1 gram of of carb it would provide not more that 5 calories per gram. so you would need 30 grams of carbs in a worst case senario. So your estimate of taking 15 g may be reasonable and count on the liver and a bit the muscles providing the rest.

Thanks. That’s a good reasoned reply. I appreciate your mentioning exercise as stress; it accounts for why BG may not go down, depending on time, degree of work.

Check out the Diabetic Athletes group here at TuDiabetes.

The question is impossible to answer without knowing how strenuously you’ll be riding, what your starting BG is, when you last bolused and a few other variables. Cruising for 15 minutes is one thing, climbing a hill for 15 minutes is another.

As a runner, 30 minutes of moderate paced running sometimes brings my BG down a few points, sometimes a hundred. And I always eat something before a run.

Your results are going to vary but I’d say eat about 15 grams before you start, carry some with you in case you feel low and definitely keep your meter handy so you can test a few minutes after the end of the ride. That’s the only way to find a reasonable estimate.

Two books might be helpful. One is “The Diabetic Athlete” by Sheri Colberg. Another is “Pumping Insulin” by John Walsh in which he writes about ‘ex-carbs’ (exercise carbs) and provides some charts describing how many carbs will cover various types and levels of exercise. The numbers are general guidelines, not absolute. YMMV.


Hi Leona,
I agree with Antony and Terry, it’s difficult to answer. 15-30 minutes on a bike, if I just want to go from point A to point B without going at top speed normally don’t influence my sugars at all. If I go very fast or uphill for 30min my sugars will actually rise a bit before dropping later. Longer trips, at normal speed make my sugars drop and I have to eat (usually 5g of fast and 5g of slow carbs every hour) But that’s just me, I know someone whose blood sugar starts to drop the moment he just looks at a bike.

It also depends on how used your body is to this form of exercise. You could prepare for a longer trip by lowering your basal in advance. You should also be aware that you can go low from exercise hours later, when your body starts to replenish its glucose reserves. This is especially dangerous if it happens during the night, because your liver won’t be able to give you a glucose boost and a glucagon shot won’t work either. It’s like drinking alcohol.


Thanks. I’ll pass on the book titles to her and look at the charts and the group information myself so I can be more knowledgeable in this. I knew you-all’d come up with the info I needed!