It is important to check blood glucose levels at least every 30 minutes during exercise
Extra carbohydrates for exercise (ExCarbs)
During most exercise (aerobic), muscles use glucose as a fuel and under normal circumstances the body makes more glucose in the liver for this to happen. With insulin use, this cannot occur if insulin levels are high as this stops the liver from being able to do this. The bottom line – carbohydrates need to be taken to balance the amount muscles are using.
One way to manage exercise is to take extra carbohydrate… but how much?
Easy Approach (based on clinical research)
Assume that muscles use glucose at a rate of up to 1 g for every kg a person weighs every hour. So for a 70 kg adult they will need to take up to 70 g of carbohydrate each hour (or 35 g every 30 minutes).
Advanced approach (actually very easy as well)
Use tables which are already on the Internet (https://www.diabetesnet.com/node/237).
These are estimated carbohydrate utilization rates per hour of activity, based on body weight. Carbohydrate intake should likely not exceed 60 grams per hour since it may promote gastric upset and hyperglycemia. Less carbohydrate intake is needed when insulin levels are lowered prior to the activity.1
1John Walsh and Ruth Roberts, Diabetesnet.com
This method is easy and works for unplanned exercise or if the exercise is more than 2-3 hours after the last insulin injection (so the bolus dose can’t be adjusted) but it may not help if weight loss is the aim.
Estimation of the ExCarbs (in grams every hour) needed to be taken with different types of exercise:
Evidence has shown that we might only be able to usefully use up to 60 g carbohydrate per hour of exercise and so if we take in significantly more than this it can lead to a high sugar after exercise. Of course, everyone is different and some really vigorous exercise might need more than this but it’s the trial and error thing again of seeing what works best for you!
We have rounded all these numbers down to 60 g but you can try more if 60 g isn’t enough.