Carb Ratios: Signs You Need to Make a Change & How to Do It

Achieving perfect post-meal blood sugars isn’t a one-size-fits-all/set-once thing; Learn if and how your carb ratio needs adjustment

If there is one thing I have learned about living with type 1 diabetes, it is that the only constant with this disease is that things are constantly changing.

Changes in schedule, diet plans, activity levels, stress levels, illnesses, hormones, and even global crises can affect how much insulin your body needs to keep blood sugars stable. And since most people aren’t living in a vacuum, these types of changes occur all the time.

So, if you want to stay on top of blood sugars, you need to be willing to change in response to them.

One area many people living with diabetes are surprised to see changes are in their insulin to carb ratios. But just as with your basal rates, how much insulin you need to take to cover a typical meal will change as your insulin sensitivity changes in response to all the factors listed above.

In this article, we look at some common signs that your carb ratio needs to be adjusted and how to make those adjustments in an effective way.

Signs You Need to Fine-Tune Your Carb Ratios

A person’s carb ratios rarely stay the same for their entire life with diabetes. In fact, most people will get to a point where they need different ratios for different meals eaten at different times. And just about everyone will eventually need to adjust their ratios up or down as their lives and schedules change.

Here are four signs to look for that may signal your carb ratio needs some tweaking or that you need to make some changes to when and how you take your meal-time insulin.

Blood Sugars Rise After Meals and Don’t Come Back Down

Fast-acting, mealtime insulins are made to mimic the slow rise and plateau of glucose in the blood following a meal. Ideally, your blood sugar and insulin will peak at the same time about an hour to ninety minutes after you finish eating. 

Within a few hours after eating, this complimentary process should bring your blood sugar back down to the level it was at before your meal.

If your blood sugar rises after a meal and fails to ever fall back into range, that is a good sign that your carb ratio for that particular meal may not be aggressive enough to properly cover your carb intake.

Unfortunately, there are a lot of factors in addition to a bad carb ratio that can affect this process. High-fat meals, undercalculated carb counts, and even bad insulin can lead to elevated post-meal blood sugars.

Instead of reacting to a single post-meal high by changing your carb ratios, make a note of the problem and consider what other factors could have played into the issue. If a bad carb ratio still seems most likely and the pattern continues multiple days in a row, then it’s time to follow the process outlined in the next section to effectively lower your carb ratio (make it more aggressive).

Blood Sugars Drop Within Three Hours After Meals

Sometimes it’s not about blood sugars rising and staying high, but instead, they rise or stay level only to plummet too low within a few hours after you have eaten.

Typically, if your sugars fall ninety minutes to three hours after you eat, an overly aggressive carb ratio is to blame.

However, just like with post-meal highs, there is always a possibility something else is to blame. In the case of low sugars following a meal, the most likely culprit is an overestimated carb count or too much activity before or after the meal.

Consider what other factors may have affected your blood sugar trend following the meal. If a bad carb ratio seems the most likely cause and the trend repeats over time, then it is time to raise your carb ratio to lower how much insulin you are taking with that particular meal.

Blood Sugars Spike High After Meals Before Returning to Normal

Another disheartening trend some people run into is blood sugar that spikes very high after a meal but still returns to normal after two or three hours. In some cases, you may even find your sugar falls too low after the initial towering spike.

This type of pattern usually has less to do with your carb ratio and more to do with how well your body is utilizing insulin at that particular time of day.

If your body is especially insulin resistant during that meal period, your cells may take longer to uptake the insulin you took with your meal. This delay in insulin activation will cause your blood sugar to spike as your meal digestion peaks. Only once the insulin begins to work will your sugars start to fall, sometimes dramatically and sometimes more slowly.

Instead of changing your carb ratio to battle this problem, it can often be more helpful to take your mealtime bolus in advance of eating. For some people, a fifteen-minute pre-bolus is enough to flatten the peak while others will need to take their bolus closer to thirty-minutes to an hour beforehand.

This type of delayed insulin activation is most common in the mornings and more likely to be seen in those with higher insulin resistance and in pregnant type 1 women.

Of course, there may be other factors at play. High glycemic meals with simple carbs are more likely to spike before insulin peaks as are meals with little to no protein and fat. But, in either of these cases, a pre-bolus will still work to reduce the post-meal spike.

Blood Sugars Drop After Meals Only to Rise Again

One of the most frustrating post-meal blood sugar patterns to deal with is when your sugars return to normal or drop too low two to three hours after a meal only to rise again before your next meal.

The most obvious cause of this issue is a problem with your basal rate for that time of day. However, there are instances when this problem stems from a bolus issue.

If the meal you ate was very high in fat, it may have taken longer than normal to digest, causing a blood sugar spike after most of your meal insulin had already peaked and leveled off. Meals extra-high in protein can also take longer to digest and may require more insulin than your carb ratio accounts for due to some protein being converted to glucose.

In either of these cases, using a prolonged square or dual bolus, or splitting your bolus if on MDI, will be more beneficial than changing your carb ratio.

How to Fine-Tune Your Insulin to Carb Ratio

If you believe that your carb ratio is in need of an adjustment after seeing a similar pattern in post-meal sugars a few days in a row, there is a simple test you can do to make to effectively raise or lower your particular carb ratio.

  1. Avoid eating anything for at least three hours before the meal in question and only begin the test if you haven’t taken a correction for at least five hours beforehand. Your sugars should be between 80 mg/dL and 130 mg/dL before your meal.
  2. Choose a meal that is low in fat and a good balance of complex carbs and some protein. Make sure it is something you can easily count the carbs for.
  3. Calculate your insulin dose based on your current carb ratio and bolus before eating.
  4. Check your sugars after two hours and again at three and four hours (if you don’t have a CGM).
  5. If at any point your sugars fall below 70mg/dL, treat the low. This may be a sign your ratio is too low or that there was some external factor interfering with the test.
  6. After four to five hours, your blood sugar should have returned to about the premeal level. 
  7. Repeat this test a few days in a row to assure the accuracy of your results.
  8. If your blood sugar after four to five hours is consistently more than 30mg/dL higher than your starting sugar, you need to lower your carb ratio by about 10%. If it is consistently more than 30mg/dL lower than your starting sugar, then you need to raise your carb ratio by about 10%.

You can then use this same procedure to test your new carb ratio. Continue to adjust until you find a ratio that will bring you back into range after your meal.

Do keep in mind, your insulin to carb ratio is meant to bring your sugars back into range following a low-fat, balanced meal. To get the same results from higher-fat, higher-protein, or simple carb meals, you will have to utilize the other tools in your belt, such as dual/square bolusing, split bolusing, and pre-bolusing.

Sara Seitz is a freelance writer specializing in blog, article, and content writing. She has had type 1 diabetes for ten years but has never let it stop her from living the life she wants. Lately, she has been busy figuring out how to manage her diabetes while raising a spirited toddler. Sara enjoys traveling, hiking and experimenting with food as a means to better health. She lives in Fort Collins, Colorado with her husband, daughter and their pack of various pets.

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