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Adjusting for GI Level

Have you noticed your child's blood glucose soar after pizza night? Are you fighting lows right after she eats pasta? Glycemicadjusting for glycemic idex index may be playing a role. You're in the right place for practical solutions...

How Do We Adjust for Glycemic Level?

From all this talk about low GI foods (see "When to Choose HiLo GI" on the previous level for critical background information), 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 foods, and there are times when you may want to steer them towards high glycemic 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.)

Tips from the trenches of type 1 diabetes
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.

tips from the trenches of type 1 diabetes

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.

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.

If you want to adjust circumstances based on the glycemic level of the foods your child eats, there are a number of different approaches you may choose to try:

1.  Construct moderate glycemic meals, 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) barley-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).

tips from the trenches of type 1 diabetesThis 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 sticky 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 food for supper, such as spaghetti, including a high glycemic 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

We have heard of no formulas nor rules of thumb that dictate what proportion of high to low glycemic 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 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) sugar cookie containing 5g of carbohydrate might not make as much of an impact when combined with (low glycemic) 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.

matching insulin to food
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 glycemic foods, or decrease the amount of low glycemic foods. Keep experimenting until you arrive at a balance you find acceptable.

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

2.  Adjust the timing of insulin based on glycemic index.

tips from the trenches of type 1 diabetes
Timing of insulin made a HUGE difference for our family. When we started “pre-bolusing” at least 15 minutes for every possible snack or meal (acknowledging that this is sometimes not possible), our son’s post-meal spikes reduced significantly (and, therefore, so did MY anxiety about those post-meal spikes!)  ~Michelle

  • 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 food arrives in the blood stream soon after eating. 
  • 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. 

Adjustments in timing of insulin may also be made based on the pre-meal
blood glucose reading: 
  • if elevated before the meal, it makes sense to leave more time between the bolus and the start of the meal; 
  • if below target before the meal, it 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 this insulin action curve to the digestion of the food. 

**Note: As mentioned above, this insulin action curve most closely matches the rate of digestion of a moderate GI meal – if eating a meal of this type, you may not need a large pre-bolus, and certainly won't need to delay bolus delivery.)

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. 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, and then making 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.

It is very important to CLOSELY MONITOR BLOOD GLUCOSE during this process, first and foremost for your child’s safety, and also for the information you glean, which will guide future decisions.

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 (for insulin pumps, and injections, respectively):

3.  Extend the meal bolus for low GI foods (Insulin Pump)

To deal with the low GI issue, if your child uses an insulin pump, some version of an extended bolus (Combo Bolus on Animas pumps, Dual Wave Bolus on Medtronic pumps, etc) 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.

tips from the trenches of type 1 diabetes

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). ~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. It is very important to CLOSELY MONITOR BLOOD GLUCOSE during this process, first and foremost for your child’s safety, and also for the information you glean, which will guide future decisions. 

Remember, the lower the first number in the extended bolus ratio, the less insulin your child is receiving up front, and therefore the more insulin she is receiving later. 
  • If you find that blood glucose is dropping quite low initially and rising too much 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 timepercentage of insulin to give with low GI foods 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. 
Again, for help in sorting all this out, consult your child’s diabetes health care team and/or pump company for guidance.

4.  Split the meal bolus for low GI foods (Injections)

If your child is not using an insulin pump, you may want to experiment with splitting or delaying the meal insulin dose.
tips from the trenches of type 1 diabetes
Before my son went on a pump, 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. 

And finally...

5.  Some foods  
require a double-whammy approach (like pizza, rich desserts and deep fried food)
matching insulin to carb with pizza
If your child eats food which is both low glycemic AND high in saturated fat,* then a double-whammy approach may be most effective. The first "wham" is to match the low GI aspect by splitting or delaying the bolus if on injections, or using an extended bolus if on a pump (see #4 and #3 above).

The second part of the equation is knowing that 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 you may also have to give more insulin 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). For more information, see The Pizza Solution under Advanced Carb Counting.

*Note: Some typical foods high in saturated fat 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.)
  • Fatty burgersEating Cheesecake with Type 1 Diabetes
  • Fatty processed meats (such as sausages)
  • Creamy sauce (those made with heavy cream or lots of butter)
  • Rich cheesecake (the full-on, high-fat variety)
  • Desserts made with a lot of real whipping cream
  • Ice cream made with heavy cream 
  • Foods/desserts made with a lot of butter
  • Foods fried in shortening, lard or bacon grease

tips from the trenches of type 1 diabetes

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. ~Danielle 
(see After Exercise for more information on combating post-exercise lows) 

Any questions? Comments? Feel free to Contact Us.

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

This material has been developed from sources that we believe are accurate, however, as the field of medicine (in particular as it applies to diabetes) is rapidly evolving, the information should not be relied upon, as it is designed for informational purposes only. It should not be used in place of medical advice, instruction and/or treatment. If you have specific questions, please consult your doctor or appropriate health care professional. 

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