What is glycemic variability and why does it matter?

Glycemic variability is the amount your blood sugar changes throughout the day. Here's why we want to keep it low for optimal health.

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We expect our blood sugar levels to exhibit some fluctuation throughout the day and between days. Food, exercise, mood, and sleep can all lead to a small rise and fall. We call these changes glucose (or glycemic) variability, and it’s a normal part of our body processing glucose.

However, the degree of variability matters.

High levels of variability will leave your glucose line looking like jagged peaks and deep ravines. That is not a state we want our body to be in, and over time it can lead to significant health problems. Instead, we want to aim for low variability: flatter valleys and low rolling hills.

The biggest impact on variability typically comes from our diet. Eating foods with added sugars or high levels of carbohydrates can cause a sudden increase in glucose, which shows up as a spike on your glucose line. This causes our body to release a relatively larger amount of insulin to move that excess to glucose out of the blood and into the cells. Often, the aftermath of a spike is a blood sugar crash as your body overcorrects for that surge with so much insulin. 

(Intense exercise can also cause a sharp rise and fall, caused by a very different process of glucose being released by the liver to fuel the muscle.)  

Why Do We Want to Avoid High Variability?

Frequent spikes and the subsequent insulin surges can cause health problems over time, including insulin resistance. Blood sugar crashes can cause more immediate effects like fatigue, depression, and anxiety.

But variability itself has negative consequences as well over the long term. Studies show that these big spikes and dips in glucose can damage tissues more than elevated but stable glucose levels. Extreme glucose variability has been linked to heart disease, diabetes, and metabolic dysfunction

This kind of variability may be more prevalent among people with “normal” glucose levels than previously realized. A 2018 study reported that 16 out of 20 participants who were classified as normal on standard clinical tests experienced severe post-meal glucose spikes that reached into the prediabetic range 15 percent of the time.

High levels of variability can also be an indication that you’re becoming insulin resistant—your body is unable to use insulin efficiently to control glucose—and this is at the root of metabolic dysfunction

Standard glucose blood tests can’t capture variability, as they take a snapshot of glucose in a moment, but a continuous glucose monitor can. 

What is the Optimal Amount of Variability?

A normal average for the magnitude of glucose excursions (difference between high and low) for someone who’s not obese and doesn’t have diabetes is between 26-28 mg/dL. In contrast, a non-diabetic morbidly obese person may have a range approaching 50 mg/dL, indicating more variability. 

We recommend trying not to exceed 110 mg/dL after a meal with no more than a 30 mg/dL rise from your pre-meal levels. Research on optimal glycemic variability for people without diagnosed metabolic impairment (such as diabetes or prediabetes) is still scant, but some studies help point us to these values. One study using CGM in people without diagnosed metabolic dysfunction found that the average postprandial glucose peak was 99 mg/dL plus or minus 10.5 mg/dL, far less than the IDF’s recommendation of 140 mg/dL. Another study using CGM in a general population found most people spent 96% of their time between 70 and 140 mg/dL.

Conclusion

Eating to maintain stable glucose levels is the best way to avoid high glycemic variability. That means avoiding refined carbohydrates and added sugar, and pairing carbohydrates with fat and protein. Other lifestyle factors matter, too, including sleep, stress, exercise. Remember that long-term trends are what’s important for overall health, so aim to have more days of stable, rolling glucose than days of high glycemic variability.

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