Fat Facts: Part 2

Many people with diabetes will tell you that fat can wreak havoc on blood glucose control. Fat doesn’t turn into blood glucose the way carbohydrate does, but it does have two very real effects on blood glucose levels.


The first effect is that fat slows down digestion. In other words, eating a high-fat meal means that it takes longer for the carbohydrate in that meal to pass into the intestine. There’s then a delay in glucose entering the bloodstream. This can lead to higher blood glucose readings later on and possible low blood glucose levels shortly after you eat your meal.

The second effect is that high-fat meals make it more difficult for your insulin to work properly. This is true whether you still make your own insulin or need to inject your insulin. High-fat meals can lead to insulin resistance. If you wear an insulin pump or take fast-acting insulin before meals, you probably know about this effect first-hand: The bolus you took to cover your Big Mac and fries didn’t cut it and you have high blood glucose readings several hours after polishing off that last French fry. It’s very common to hear that people often struggle with certain meals, such as pizza or Chinese food, because they’re challenging in terms of how much insulin to take to “cover” them.

There’s no set science for figuring out how to adjust insulin boluses for high-fat meals. Much of this is figured out on a trial-and-error basis. In fact, I have a friend who, after starting on a pump, had to go to his favorite pizza place and order the same pizza five times (no great hardship there) before he learned how to bolus correctly, using the “extended wave” feature on his pump. If you’re a “pumper,” you likely will need to use the extended wave feature on your pump to handle high-fat meals. This feature allows you to bolus some insulin with your meal and then deliver more insulin after you finish your meal. Most pumps these days have this feature.

Let’s say you’re going to eat your favorite holiday meal, laden with high-fat goodies. After figuring out how much insulin you need to cover the meal, you might try bolusing half of your dose up front and then extending the other half of the dose over the next two hours. By checking your blood glucose a couple of hours after the meal and then again four to six hours after the meal, you’ll get a pretty good sense of how that worked. If your blood glucose levels are running high four to six hours later, for example, you might know next time to take less insulin before your meal and spread the rest of it out for a longer period of time. My husband, who wears a pump, finds that taking about 25% of his bolus dose before a high-fat meal and 75% over about four hours works pretty well. Everyone is different, though—hence the trial-and-error approach and the importance of blood glucose monitoring.

Speaking of pizza, a study was actually done looking at various methods of bolusing for pizza meals. The researchers found that using the “dual-wave” bolus feature on the pump, extended over eight hours, worked well in controlling “post-pizza” hyperglycemia (high blood glucose levels).

Not on a pump? You can improvise and cover high-fat meals by splitting up your injection of fast-acting insulin (such as insulin lispro [Humalog], insulin aspart [NovoLog], or insulin glulisine [Apidra]). Some people even take both fast-acting and Regular insulin (which has a slower action time) for high-fat meals.

However, talk to your health-care team before trying either of these approaches. Your physician or dietitian should be able to work with you to come up with the best strategy to handle higher-fat meals and keep you safe at the same time. Also, don’t forget to monitor your blood glucose levels and keep good records. Remember: practice makes perfect!

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  • diabeticguy

    The comments about fats in this article and the previous one are biased against fats, which are critically important nutrients vital healthy bodily functions. It is true that fats slow digestion of carbohydrates–and that is a good thing for diabetics because it means less volatility in blood sugar levels, even if it may take a extra attempt to get the pump dosing right– that is a problem with the pump, not with fats! Humans have evolved to depend on fats, including satured animal fats, while the agricultural revolution that brought us endless grain supplies is only 5000 years ago. According to latest research, the most dangerous fats are trans fats, which are artificial industrial creations- these are extremely destructive and should be eliminated from the diet. Research has NOT demonstrated that saturated fats make you fat, or cause heart disease; sat. fat is natural and required in human diets. Diabetics, research this matter on your own–adding fats has improved my control.

  • Chrissie in Belgium

    There is so much talk about counting carbs and so little about the effect of fat and protein on blood sugar values. I appreciate all discussions concerning how to correctly calculate meal boluses for meals including fat and protein. As you mention, each diabetic reacts differently. My bg values rise significantly 6 hours after a meal containing even small lean protein foods! Furthermore the bg rise does not follow a really consistent pattern in time or amount! I do not think I am the only one with this problem. Pls talk more about the effects of protein and fat on our bg values. Thank you!

  • acampbell

    Hi diabeticguy,

    Thanks for your response. The point of my previous two blogs on fat was not to imply that all fat is bad. Olive oil, canola oil, and fish oils are examples of heart-healthy fats. However, there is a wealth of evidence that links a diet high in saturated fat with heart disease. And all fats, whether they’re saturated or unsaturated, have 9 calories per gram, higher than carbs and protein. Finally, high-fat foods can present a challenge to people with diabetes in terms of blood glucose control. Again, the implication is not that high-fat foods have to be avoided, but that people must learn how to fit these foods into their eating plan while minimizing extreme high (or low) blood glucose levels later on.