Choose the Right GI for the job

The Glycemic Index: when to eat high vs low GI foods + the effect on blood glucose

If the goal for managing T1D is to have the right amount of insulin, at the right time, to cover the food we eat, then sometimes a high glycemic index, quick-digesting food is exactly what’s needed. But sometimes high GI foods should be avoided and slower-digesting foods should be embraced. Here we discuss which time is which, and how to choose the right glycemic index value for what your child needs in this moment.

As we discussed in The Glycemic Index Explained, the goal for managing type 1 diabetes is to match insulin action with the rate of digestion of the food, so that you have the right amount of insulin, at the right time, to cover the food eaten. With that in mind…

When Are Low GI Foods Useful?

  • If your child’s blood glucose is above target when he plans to eat, steering him toward low GI foods will allow more time to correct BG toward the target (while also lessening a further spike in blood glucose).
  • If your child uses N/NPH as background insulin, the morning injection creates a peak at lunchtime, but this peak doesn’t accommodate the fast rise in BG following the lunch meal. So having low GI foods at lunch better match the insulin action of NPH, resulting in closer-to-target blood glucose readings 1-2 hours after lunch.
  • If the usual 15-minute pre-bolus is not possible (for example, your teen rolls out of bed at the last minute and eats breakfast on the way to school), making low GI choices available may help tame the post-meal spike.
  • If a scheduled snack comes soon after a meal, and blood glucose has not had a chance to return to target range, a snack low on the glycemic index may help flatten the spike in blood glucose that would otherwise occur after the snack.

Tips from the Trenches

My son’s school snack is scheduled for 9:30am, which is only an hour and a half after he finishes breakfast. At this time, his blood glucose is often still above range – if we add a high GI snack at this time, his blood glucose is likely to shoot upward from an already-high starting point. To help mediate this, we choose to send school snacks that are either low carb, or low GI.
~Michelle

When Are High GI Foods Useful?

There are times when (slowly-digesting) low GI foods are actually counterproductive, and (quickly-digesting) high GI foods may be more appropriate:

  • High glycemic foods and drinks are most appropriate for treating low blood glucose.
  • When your child comes into a snack or meal with a blood glucose reading that is below target (but not actually low), a high GI snack may help avoid the potential low that would occur if blood glucose were to continue to drop.

Tips from the Trenches

I generally send low carb or low GI snacks for my son’s school snack. However, for days when he comes into snack-time below target, we keep a supply of high GI crackers on hand at school so he can eat these before or instead of the snack that I have sent for that day.   ~Michelle

  • Often low blood glucose is accompanied by an irresistible craving for food; after treating the low, your child may still be ravenous, and you may be unable to prevent them from eating a snack NOW, without waiting the recommended 15 minutes after the low treatment.

Tips from the Trenches

If my son eats a follow-up snack within the first 15 minutes following a low treatment, I have found that it works out best to steer him towards high GI foods, such as a white bun with jam (with insulin to cover this post-low-treatment snack). If he eats something like whole grain crackers with peanut butter (low GI), he tends to recover more slowly from the low, the irresistible hunger persists, so he tends to over-eat for the post-low snack. The result is often a bigger spike in blood glucose (low rebound) later.   ~Danielle

The above information was reviewed for content accuracy by clinical staff of the Alberta Children’s Hospital Diabetes Clinic.