What is a Post Meal BG Spike?

Post-Meal Blood Glucose Spikes: what they are and how to find them

Michelle MacPhee
M.S. (Applied Psychology)
D-Mom, Creator/Co-Founder of WTD

A post-meal spike refers to the temporary high blood sugar that occurs soon after eating. These post-meal highs occur because of a mismatch between the rate at which food raises blood sugar, and the rate at which insulin acts to balance the BG-raising effects of that food. But what qualifies as a spike? How do I know if my T1D child's BG is spiking? Why do spikes happen? Do spikes even matter?

What number qualifies as a “spike”?

Post-meal, or “post-prandial,” blood glucose is the amount of sugar in the bloodstream after eating.

The Diabetes Canada 2018 Clinical Practice Guidelines recommend, for all children and adolescents under the age of 18 with type 1 diabetes (T1D), a pre-meal plasma glucose target of 4.0 – 8.0 mmol/L, with 2-hour post-meal target of 5.0 – 10.0 mmol/L. In their 2018 Clinical Practice Consensus Guidelines, the International Society for Pediatric and Adolescent Diabetes (ISPAD) recommends the same post-prandial target of 5.0-10.0 mmol/L.

With these recommendations in mind, anything over 10.0 mmol/L (2 hours after eating) would qualify as a “spike”. (Though as a parent, I personally wouldn’t be too concerned with an occasional post-meal BG around 10… when it’s over 12 or 14, that’s what gets me moving into solution mode.)

As parents, we realize what a tall order it can be some days to land under 10.0, especially for younger children. So if you have a preschooler with diabetes, don’t panic! If "under 10.0" is an unattainable goal for your family, you could adopt graduated post-meal glycemic targets based on your child’s age, targets that get tighter as your child gets older. In his article Strike the Spike: Controlling Blood Sugars After Eating 2, Gary Scheiner (MS, CDE) suggests from his clinical experience the following goals for post-meal glucose for children and adolescents (1-2 hours after eating):

  • <13.9 mmol/L for Preschool/Toddlers (5 years old and younger)
    i.e. rise of fewer than 8 points from the median pre-meal target of 6.0

  • <12.5 for School Age Children (6-11 years old)
    i.e. a rise of fewer than 6.5 points from before eating

  • <11.1 for Adolescents (12-18 years old)
    i.e. a rise of fewer than 5 points from before eating

Bear in mind that glycemic targets for kids should be individualized. Check with your child’s diabetes health care team, as they may adjust that target upward to meet your child’s unique needs and circumstances, particularly if she has had severe or excessive hypoglycemia or is not aware of her lows (hypoglycemia unawareness).

How do I know if BG is spiking?

To know if blood sugar is rising too high after eating, you need to find the post-meal peak, and compare it to your child’s target post-meal blood sugar goal.


According to CDE and blood glucose management expert, Gary Scheiner:

The post-meal BG peak is the net rise in blood glucose that occurs from before eating to the highest point after eating.

For a valid test, use a “typical” meal for your family, one that does not have more fat than usual (as fat can affect blood sugar significantly); the food should be consumed within 30 minutes; also, once you’ve delivered insulin and the meal has started, take no more food or insulin until the test has been completed. (A snack an hour after supper will confound the results.)

If your child wears a Continuous Glucose Monitor (CGM), your detective work to find the peak is straightforward: 3 hours after eating, simply view the glucose trace from then back to the time she started eating; note the point at which the readings plateau and then fall – this highest point of the CGM trace is the peak. Record the glucose reading and time since your child finished eating. Compare the glucose number to the recommended post-meal targets above to see if your child’s glucose is spiking (going too high) after meals. Repeat this process across multiple days and/or meals (or snacks) to discover any trends and to pinpoint the problem.

Does your child’s BG fall in the early stages of the meal, before rising?

You can obtain the same information without CGM, it just takes a little more investigation and a few more fingersticks than usual: Check BG before your child eats, at 1 hour after eating, then again at 2 and 3 hours. The highest glucose reading you find represents the BG peak for that meal. Make note of the number and the time after eating at which it occurred. Again, repeat this process across multiple days and/or meals (or snacks) to see the trends and problem areas.

  • If that all sounds like more effort than you’ve got to give right now, then just check BG at 2 hours post-meal; that will tell you if BG is spiking and give you a sense of what’s going on after meals.

  • If you really want to get precise, for a given meal you could check before eating and then every 30 minutes after eating until two consecutive drops in blood glucose occur.

If you find that on various days and/or for various meals, BG consistently rises within the first 1-2 hours post-meal (within the ranges recommended above) and then returns to target range, then all’s well, there’s no need for change. Further, occasional BG spikes are to be expected when you’re living with T1D, and will not have a significant impact on future health. But if you find that post-meal glucose is consistently higher than recommended, then it would be wise to make some changes.

Why do spikes happen? Are they really that bad?

For all of us, even those who do not have T1D, the amount of sugar in our blood increases after we eat: the food is broken down through the process of digestion, and the sugars that result from carbohydrate digestion enter the bloodstream, where they are transported to all the cells in all the tissue and organs in our body. For those without type 1 diabetes, the hormone insulin is released immediately, acting as the key to unlock the door to each cell; sugar leaves the blood stream as it moves into the cell, feeding the cell and providing the fuel to create energy.

If this sugar is moved quickly and efficiently into the cells, then blood glucose rises a bit, rides a gentle curve, and comes back down. The post-meal rise in blood sugar for those without T1D is minimal. But for our kids with diabetes, endogenous (internally-produced) insulin is missing1; we need to inject/infuse it, so the efficiency of the process takes a hit. As Gary Scheiner points out in his article Strike the Spike (New and Improved) 3, this inefficiency is “like a batter with very slow reflexes facing a pitcher who throws 98 mph fastballs: the timing is all fouled up.” Glucose piles up in the blood stream, not moving quickly enough into the cells where it can actually be used, resulting in high blood glucose (BG), which if it sticks around creates a large, wide post-meal BG spike.

Research suggests that 3-hour post-meal readings may predict the HbA1c reading more than pre-meal readings, so a key factor in managing BG effectively involves paying attention to what happens to blood sugar after our kids eat.

The higher those BG spikes, and the more often they occur, the more of a negative impact this can have on long term health, increasing the risk of diabetes-related complications. Also, in the short term, high blood glucose feels crummy, creating headaches, lack of energy, poor coordination, fuzzy brain, low mood, sadness, and poor frustration tolerance. (Sibling battles, anyone?)

But take heart! We have the power to reduce the size and frequency of post-meal spikes, and give our kids the best chance to feel good, to reach their own potential, and to protect long term health...

Notes & References:

  • In addition to the lack of insulin, individuals with type 1 diabetes are also missing the hormone amylin, which slows down the movement of food into the intestine, thereby slowing down the process of digestion and better matching the insulin timing to the rate of digestion of food. So if you think “flattening the curve” is an intricate science and art that doesn’t always turn out as it should… you’re right! Be gentle with yourself when post-meal spikes still occur despite your family’s best efforts.

  • Gary Scheiner, (2019) Strike the Spike: Controlling Blood Sugars After Eating

  • Gary Scheiner, (2010) Strike the Spike, New and Improved.