Blood Glucose Spikes: Glycemic Index

Tame Post-Meal BG Spikes caused by high or low GI foods

Michelle MacPhee
D-Mom, Creator & Co-Founder of Waltzing the Dragon

Have you noticed your T1D child’s blood glucose soar after pizza night? Are you fighting lows right after she eats pasta? Glycemic index may be playing a role, which may be compounded by the fat content of those foods. If the rate at which food is digesting doesn’t match the insulin action, then blood glucose can swing wildly. But the good news is that changing your strategy will reduce the swings!  Here are some practical solutions to tame those blood glucose spikes after eating high or low glycemic index (GI) foods.

Glycemic Index and Type 1 Diabetes

From all this talk (in the background information) about food that is low on the Glycemic Index (GI), it’s easy to assume that the goal is to eat only low GI foods. But that is NOT what we want you to take away from this reading. There are times when you may choose to steer your child toward low glycemic index foods, and there are times when you may want to steer them towards high glycemic index foods (more on that below).

There are also times when you want them to eat whatever your family would be eating if the diabetes dragon hadn’t complicated things so much! You may want your child to have the freedom to eat, without having to restrict her options based on the fact that she has diabetes. In those times, if you know how to respond effectively, the inescapable fact that your child has diabetes doesn’t mess things up so much (with unexpected post-meal lows, or extreme or persistent post-meal highs).

(A short but relevant tangent… individuals with type 2 diabetes are more reliant on a low-fat, low-GI, lower-carb diet than those with type 1. Type 1’s are able to eat the same things as appropriate for their peers who do not have diabetes – eating good food is good for all of us; kids with type 1 diabetes are no more restricted in eating fat, carbs, and high GI foods than anyone else is.)

Tip from the Trenches

One of my son’s favourite foods is pizza but for a long time after diagnosis I cringed whenever he asked to eat it. It would cause his blood sugars to skyrocket up to 8 hours later and it would take what seemed like forever to bring him down to a normal number.   ~Danielle

For the first two years post-diagnosis, our son’s post-pasta spikes were mystifying to us, and became just another of the multiple variables adding to the blood glucose management confusion that was muddling us up. When we started sorting out the impact of low GI foods, such as pasta, one variable was removed from the muddle, making it easier for us to sort out the other variables.   ~Michelle

The point that we are making is that an awareness of differing GI levels may help explain some seemingly inexplicable post-meal blood glucose swings. In addition, you MAY choose to use this awareness to modify your family’s eating habits and/or how you deliver insulin when eating foods with either a high or low GI value.

How Do We Reduce Blood Sugar Swings?

If you want to adjust your approach based on the glycemic index of the foods your child eats, here are a few different approaches you could try:

1. Make Your Meals Medium GI

Moderate-GI meals corresponds most closely to the insulin action curve of today’s rapid-acting insulin, thereby reducing the swings that result from meals that are primarily either high or low on the glycemic index.

A medium GI meal can be constructed either by serving mostly foods which are medium GI by nature, OR by combining low GI with high GI foods. For example, including watermelon (high GI) or sugar cookies (high GI) for dessert with a (low GI) pasta-based meal will result in a meal that is more moderate GI overall. The same is true for serving mashed potatoes (high GI) with roast beef, rich gravy (low GI) and corn (low GI).

We have not heard of any formulas nor rules of thumb that dictate what proportion of high to low glycemic index foods you need to arrive at a moderate GI meal overall, but in our own experience it seems to make sense that roughly (VERY roughly) equal proportions of high and low glycemic index foods, based on the carb content they contribute to the total meal, result in a more or less medium GI meal. For example, eating 1 (high glycemic index) sugar cookie containing 5g of carbohydrate might not make as much of an impact when combined with (low glycemic index) pasta containing 40g of carbs, compared to eating 30g of carbs in fluffy French bread (high GI), along with the same 40g of carbs from pasta; the latter is more likely to result in a moderate GI meal.

The only way to see what will work well for your child is to try a combination of foods and record the resulting blood glucose pattern. If you are still seeing a significant drop in blood glucose followed by a significant rise, you may need to increase the amount of high GI foods, or decrease the amount of low GI foods. Keep experimenting until you arrive at a balance you find acceptable.

Tip from the Trenches

This is my favourite solution, and the one I find easiest to achieve for our family. If we are having rice for supper, choosing a white basmati version (moderate GI) as the main source of carbohydrate at the meal seems to avoid the huge spike we get if my son eats regular white rice (high GI), as well as avoiding the blood glucose drop and then later spike that we get if he eats Uncle Ben’s Converted rice (low GI). Alternatively, if I am planning a low glycemic index food for supper, such as spaghetti, including a high glycemic index food, such as white French bread, seems to be helpful to bring the glycemic value of the whole meal up to a medium GI level. ~Michelle

If constructing moderate GI meals doesn’t resolve the issue, instead (or in addition) you could…

2. Adjust the Timing of Insulin Delivery Based on Glycemic Index

A standard recommendation for many individuals with type 1 diabetes is to deliver the insulin dose 15 minutes before the start of the meal. However, this timing may be adjusted to account for the glycemic index value of the foods you are about to eat.

High GI Foods

If it takes very little time for high GI foods to start raising blood glucose, then it makes sense to deliver the meal insulin (bolus) well in advance of the start of the meal or snack (longer “pre-bolus” time period), to give the insulin a chance to start working before the high glycemic index food arrives in the blood stream soon after eating.

Low GI Foods

On the other hand, if low GI foods take some time to start raising blood glucose, then it makes sense to deliver the meal bolus relatively later when eating low GI foods, perhaps even after your child has started eating, so that the insulin doesn’t start peaking before the food starts digesting.

Tip from the Trenches

Timing of insulin has made a HUGE difference for our family. When we started “pre-bolusing” at least 15 minutes whenever possible, our son’s post-meal spikes reduced significantly (and, therefore, so did MY anxiety about those post-meal spikes!) Sometimes for high GI foods we pre-bolus as much as an hour before eating (based on our previous experience with that particular food.)   ~Michelle

Adjustments in timing of insulin may also take into account the pre-meal blood glucose:

If blood sugar is elevated before the meal… makes sense to leave more time between the bolus and the start of the meal.

If blood sugar is below target before the meal… makes sense to leave less time between the bolus and the start of the meal.

What do we mean by “soon”, “later”, “less time” and “more time”? There are no universal rules that work in every case, however, to arrive at an appropriate timing balance, bear in mind that rapid-acting insulin (used as bolus insulin in most cases) starts to work about 15 minutes after delivery, and peaks about 1 hour after delivery. Your goal is to match the insulin action curve to the digestion of the food, and as mentioned above, the curve for rapid-acting insulin most closely matches the rate of digestion of a moderate GI meal.

We have found the chart on “Adjustments to bolus timing based on GI and pre-meal blood sugar” in Gary Scheiner’s book Think Like a Pancreas to have very helpful guidelines for timing.  (More info under #5 in 14 Strategies to Reduce Post-Meal Spikes.)

From there, we recommend recording: the foods eaten; the timing and amount of insulin delivered; and the resulting blood glucose pattern at different times after eating. Then you can make adjustments for future meals based on those results. If you are still seeing a significant drop in blood glucose followed by a significant rise, this may mean the insulin is peaking before the food, so you may need to decrease the pre-bolus period. Keep experimenting until you arrive at a balance you find acceptable.

In addition to modifying the GI level of the whole meal (#1, above), and/or timing insulin delivery (#2, above), to smooth out post-meal blood glucose readings you may want to split or extend the food bolus (which you can do with either injections or an insulin pump):

3. Extend the Insulin Bolus for Low GI Meals

Extending the meal bolus involves spreading out the delivery of onsulin so that, instead of being given at the same moment in time, in a single dose, the total amount of insulin is split up into more than one dose, and delivery is spread out over time. The actual process of extending the bolus looks different for injected insulin vs. insulin pumps.

a. Splitting the bolus – Injections

If your child is on injections for insulin delivery, you may want to experiment with splitting the meal insulin dose into two or more separate doses, or delaying the meal insulin dose for a period of time after the food has been eaten. Consult your child’s diabetes health care team for guidance on splitting the meal bolus to deal with low glycemic meals, but here’s what worked in our experience…

Tip from the Trenches

When my son was on injections, we started the experiment with splitting injections for low GI foods by giving, for example, half of the meal insulin with the meal and the other half 2 hours later. We noted the results and tweaked the amount and timing of the split dose. Through this process of trying one thing and then adjusting based on the result, we found a nice balance for the split doses that kept my son’s blood glucose closer to his target range.  ~Danielle

b. Extending the Bolus – Insulin Pumps

To deal with the low GI issue, if your child uses an insulin pump, some version of an extended bolus (a.k.a. Combo Bolus, Dual Wave or Square Bolus, Extended Bolus) may be helpful. An extended bolus allows you to specify what portion of the total bolus you want delivered immediately (up front); then the remaining amount of the total bolus will be spread out over the time period specified. Consult your child’s diabetes health care team and/or pump company for guidance on using extended bolus functions, but here’s what worked in our experience…

Tip from the Trenches

We started the combo bolus experiment for pasta, for example, by splitting the bolus into a 50:50 combo over 3 hours (50% of the meal bolus delivered immediately (up front), and the other 50% spread out over the next 3 hours). We then tweaked the process only slightly from there.   ~Danielle

As always, to find the right balance for your child you will need to experiment with each target food and note the results for each food, adjusting future actions based on those results. Again, it's very important to CLOSELY MONITOR BLOOD GLUCOSE during this process, first and foremost for your child’s safety, and also for the information you gain, which will guide future decisions.

Remember, the lower the first number in the extended bolus ratio (the “40” in a 40:60 split, for example), the less insulin your child is receiving up front, and therefore the more insulin she is receiving later, during the extended portion of the bolus. This is key to understanding how to tweak the numbers based on the results of your experimentation:

  • If you find that blood glucose is dropping quite low initially and rising too high later, you may need to change the proportions of the extended bolus to give less insulin up front, or you may need to alter the time period over which the extended portion of the bolus is delivered. For example, if you start with an 80:20 split, and your child’s blood glucose drops significantly after eating, you may want to try a 70:30 split, or 60:40, or whatever other ratio seems appropriate based on previous results.
  • On the other hand, if your child’s blood glucose first rises significantly after a meal, and then drops significantly a few hours later, that may indicate that she is not getting enough insulin up front, and is getting too much insulin in the extended portion of the bolus. For example, if you started with a 50:50 split and blood glucose first rose significantly, then dropped significantly, you may want to try a 60:40 split, or 80:20.

When Fat Content Complicates the Issue…

When your child eats food which is both low on the glycemic index AND high in saturated fat… a double-whammy approach may be most effective.

The first “wham” deals with the low GI nature of the food as described above, by splitting or delaying the bolus if on injections or by using an extended bolus if on a pump.

The second “wham” involves giving more insulin to deal with the effects of saturated fat. Saturated fat causes insulin resistance about 6-8 hours after eating (the more saturated fat consumed, the more pronounced the insulin resistance becomes). This means that more insulin may be needed later to deal with the high fat aspect (in the form of an injected correction dose, or a Temporary Basal function on an insulin pump).

More on Dealing with Tricky Foods & High Fat Foods:

Which foods are high in saturated fat?

Some common high-fat foods, which may require a double approach to minimize post-meal spikes, include:

  • Pizza (the more cheesy the pizza, plus the greater the number of high-fat meat toppings, the more saturated fat it contains. For eating out, this varies greatly from restaurant to restaurant. In our experience, Boston Pizza tends to use much less cheese compared to Panago, and thus is lower in saturated fat, resulting in relatively less insulin resistant post-meal.)
  • Burgers
  • Nachos (the tortilla chips and the cheese may have a high fat content)
  • Cheese buns (sometimes - depends on what type and how much cheese is used)
  • Fatty processed meats (such as sausages, pepperoni, bacon, some packaged hams)
  • Creamy sauce (those made with heavy cream or lots of butter - think Fettucine Alfredo)
  • Rich cheesecake (the full-on, high-fat variety)
  • Desserts made with real whipping cream
  • Ice cream made with heavy cream; ice cream treats/bars (like Magnum, Hagen Daaz or Klondike bars)
  • Chocolate bars (sometimes)
  • Peanuts
  • Foods/desserts made with lots of butter
  • Foods fried in shortening, lard or bacon grease (which could include French Fries, Hashbrowns, Deep-Fried Fish, etc)
  • Potato Chips, Nacho chips (like Doritoes)

Tip from the Trenches

I try to use foods high in saturated fat to our benefit. I will pick up really cheesy pizza for supper after Paul’s had a big exercise day such as skiing because it counteracts the post-exercise nighttime lows.

More on combating post-exercise lows:


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