Foods’ Strange Tricks

You sit down to eat. How will your meal affect your blood glucose? If you’re on insulin, how much should you take? Turns out that counting carbohydrate will not always give you the answer. Food can affect you in strange ways.


Do you know about the pizza effect? In a blog on glycemic index, I mentioned how plain pizza had a much higher glycemic index than a deluxe pizza with all the toppings. Plain dough and sauce raises your blood glucose way faster.

What I didn’t mention was that all that carbohydrate in the deluxe pizza will get into your bloodstream eventually. You just don’t know when, unless you check your blood glucose every hour for four hours or even more. That’s because the fats and protein in the toppings slow down the absorption of carbohydrate. As a result, your blood glucose might spike two to five hours after the meal.

Other meals that combine lots of carbohydrate with fats and/or proteins could have the same effect. Jan Chait posted here five years ago about a big spaghetti fest she had with her husband. The pasta was covered with a fatty sauce, with a side of garlic bread and lots of butter. Because of the fats (the pizza effect,) her blood glucose levels were up for two days, instead of just spiking high for an hour or two.

One commenter posted on that he injected enough insulin to cover the carbohydrate in a big Chinese meal, including lots of fried food. Two hours after eating, his glucose was 171, the same as it had been before the meal. But three hours later his sugar was over 500! It took him days to get back in control.

Sometimes the pizza effect is helpful, like at bedtime. A bedtime snack that includes a small amount of fat and protein can help keep overnight levels from going too low. That way you don’t get a rebound effect in the morning.

If you’re not taking insulin, a delay in rising glucose is often a good thing. Your body will have more time to crank up its phase 2 insulin response. But that doesn’t always work. If the delayed spike happens all at once, your insulin might still be overwhelmed.

If you are taking insulin, the pizza effect is an even bigger deal. You might inject insulin to cover the first 1–2 hours after your meal, but the carbohydrate in the meal will not be in your blood yet. So you might go low. Then a couple of hours later when the glucose kicks in, the insulin will have worn off, and you’ll be way too high.

On Health Central, a person helping her son use a continuous glucose monitor (CGM) found out that he needed to take a small amount of insulin immediately, then take an extended bolus for up to six hours, to avoid spiking.

Science writer Gary Taubes wrote that high glucose numbers after a fatty meal aren’t the fault of the fat. In Taubes’ view, fats won’t cause a glucose rise without the carbohydrate. If you just ate the pizza toppings and not the crust, you’d be OK.

There may be more to the pizza effect than just delayed carbohydrate absorption, though. Studies show that eating fats can increase inflammation and insulin resistance.

Not everyone experiences the pizza effect. This comment thread features many people with diabetes saying they never experienced the effect, though they ate pizza and monitored frequently to look for it.

Chinese Restaurant Effect
The pizza effect is not the only thing that can throw you off. Dr. Richard Bernstein described what he called the “Chinese Restaurant Effect,” in which glucose levels spike far higher than a low-carb meal could have possibly caused.

Bernstein cites a person with Type 1 whose glucose went from 90 to 300 after eating a head of lettuce. Lettuce has very little carbohydrate content, so how could this happen?

Bernstein explains:

The upper part of the small intestine contains cells that release hormones into the bloodstream whenever they are stretched, as after a large meal. These hormones signal the pancreas to produce insulin in order to prevent the blood sugar rise that might otherwise follow digestion of a meal. Large meals cause greater stretching of the intestinal cells, which in turn secrete larger amounts of these hormones.

Since a very small amount of insulin released by the pancreas can cause a large drop in blood sugar, the pancreas simultaneously produces the less potent hormone glucagon to offset the potential excess effect of the insulin.

Glucagon raises blood glucose by telling the liver to break down starch into glucose. So the two hormones should balance out, but in a person with diabetes, the insulin won’t kick in, just the glucagon. So eating large amounts of anything, “even sawdust” says Bernstein, could raise your blood glucose.

Seems like it’s best not to eat big meals at all, to avoid the Chinese Restaurant Effect. To avoid the pizza effect, if you are going to eat things like pizza, keep the portions small and check your blood glucose several times in the hours following, because you don’t know when you’ll spike. Make sense?

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  • Deb

    This stuff just gets more complicated all the time (well, I guess it’s just my awareness of it). So testing two hours after a meal is not enough for some meals. Since Medicare will only let me have 1 strip per day, I guess I’ll have to go out and buy more test strips to see how these weird effects hit me. Thanks for clarifying this, David. I think.

  • Margret

    Medicare only covers 1 test strip/day??? Holy crap. If I don’t die before then, I’m certainly going to have some major health issues after I go on Medicare. That, or I won’t be able to afford food because I’ll be buying test strips off the shelf, trying to maintain my health.

    Good info on the pizza and Chinese Restaurant effects.

  • John Rollins


    An earlier article on reduced cost glucose meters and strips at Walmart comes to mind. Maybe that could fit your budget if you want to increase the frequency of your blood sugar tests.

  • whatnext

    My advice is to NOT EAT the pizza. I have been avoiding carbs since my Type 2 “pre-diabetic” diagnosis 8 years ago. I am not on any medication or insulin. When I eat pizza, I eat just the toppings. You get the Pizza “experience” without the blood sugar mayhem. I don’t understand why every Diabetic doesn’t follow a Low-Carb eating style. For me, all it took was seeing my readings after eating carbs. I swore off bread, other grains,many fruits and starchy vegetables.I test a lot to gauge the effect of food on my readings, and I have adjusted my diet accordingly.Of course, it’s not very easy, but it’s doable, and it WORKS.

  • David Spero RN

    Deb, if you can only afford one strip a day, it doesn’t make much sense to test at all. In my opinion, it would be better to save up for a few days, then use three or four to monitor your after-pizza sugars, or whatever it is you’re trying to find out.

  • Ferne

    Medicare will pay for more than 1 strip a day if your doctor orders it. My doctor ordered twice a day for me and I have to keep a log for a month every 6 months that is sent to Medicare. If a log is not kept and sent in Medicare will not pay.

  • Daniel Stevens

    Wow! Great article. I’ve been researching on the Internet for months re ‘the pizza affect’. I’m a massively suffer from this strange affect. I was an insulin injection type 1 diabetic for 15 years with Hba1c’s of 6.3 for years, however I fell into the brittle diabetic category and moved onto a pump over the last 3 months.
    Theres a few things That have amazed me since the move to my pump. The first is how little a Hba1c test really tells the doctor what’s going on. I’ve been eating pizza for many years. When I ws injecting I had to double what my normal dose was, and check up to 5 hours later usually finding it still would plateau fairly high. The second, even though I thought I knew my diabetes, my body and how to control my Hba1c very well. I didn’t. I didn’t. I was lucky!
    Thanks again for a good article. I feel safer having read it.

    Dan Stevens

  • Steve

    Whatnext –
    I follow a low-carb diet by limiting the amount of carbs I eat, focusing on vegetables and some fruits. But, I believe carbs are necessary to provide fuel and I maintain a fairly high level of cardio exercise. Marathoners say they run so they can eat pasta – sort of the same thing for me. Moderation in all things. Cheers.

  • PrickThis

    Quite a booming industry some diseases (dysfunctions) have become.

  • Anon Coward

    “Pizza and Blood Sugar Control: (Not Quite) Easy As Pie” – Gary Scheiner, MS, CDE – T1U »

  • Ollie Tucker

    I was taking Lantus insulin in the evening for over a year. Then I turned vegetarian, almost vegan, and went off my insulin because it was making blood glucose levels too low. My problem is that even though my bg level stays great all day, I have a high fasting bg in the mornings upon waking. it is always 120 to 145. I take metformin 1000mg in am and evening. Don’t know how to control the morning high. Don’t want Dr to put me back on insulin. I eat a very, very healthy diet. Lots of dark green leafy vegies, no meat, protein from beans, nuts, seeds and grain products but am also watching carb intake. My Ac1 was just taken and it was 6.4. Am I in trouble???

  • David Spero RN

    Ollie, I’m not sure — you should ask your MD or DE, but this certainly sounds like dawn phenomenon. I’d be interested what other think, but I’ll bet if you took your evening metformin later, or split it in two doses and talk half sometime in the middle of the night, that would solve your problem. A tablespoon of vinegar at bedtime might do it, too.

  • Cynthia

    For those worried about the 1 strip a day provided by Medicare. Check out the meter and strips that are Walmart’s brand. Cost less than my husband’s co-pay on the name brands.

  • Sabrina

    Reli-on prime..its a $16 monitor and $9 for 50 strips!

  • Sherry Ledet Thornburg

    I’m new to all this wish the diabetes of America nutritionist would have told me about this instead of just saying fats bad. Alittle more explanation would have been helpful.

  • John Debba

    I’m 100% sure the dietician instructed Sherry on carbs affecting blood sugar