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What is the connection between low-carb diets and blood sugar?


Updated May 21, 2014

Cut watermelon in a desert cup
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Question: What is the connection between low-carb diets and blood sugar?
Answer: Low-carb diets are all about blood sugar (blood glucose). Basically, we eat low-carb diets to keep our blood sugar normal and stable. To fully understand the connection, it's helpful to first familiarize yourself with how the body processes blood sugar.

What Do Carbohydrates Have to Do With Blood Glucose?

Everything. All foods with carbohydrate -- whether rice, jelly beans, or watermelon -- break down to simple sugars in our bodies. This is what causes our blood glucose to rise. The carbohydrate in most starchy foods (potatoes, bread) is simply a collection of long chains of glucose, which break down quickly and raise blood sugar.

What Do Our Bodies Do When Blood Sugar is High?

When our blood sugar goes up, our body responds by secreting insulin to stabilize it. The sugar is then taken out of the blood and converted into fat; insulin's primary function is facilitating the storage of extra sugar in the blood as fat.

What are the Problems with Blood Sugar Going Up?

For many people, this system works fine. Sometimes, though, people reach a point in their lives when it goes awry (or it doesn't work well from childhood). This is called insulin resistance, and one of the consequences is that there gets to be too much insulin in the blood as the body tries harder and harder to bring the sugar down.

When insulin is high, weight gain is more likely, since a main function of insulin is fat storage. Conversely, people with high insulin levels are more likely to lose weight on low-carb diets.

Keeping blood glucose normal has other health benefits, such as the prevention of heart disease and diabetes. Even non-diabetics have an increased heart disease risk with higher blood glucose levels.

Learn more about insulin resistance, diabetes, and prediabetes.

What About the Glycemic Index? Doesn't that help separate "Good" Carbs from "Bad" Carbs?

The glycemic response of the body to a carbohydrate is important. Although the glycemic index has its limitations as a tool, it can give a rough idea of how your body may respond to a given food. However, remember that serving size is also important. Eating a whole lot of a low glycemic carbohydrate food will still raise your blood glucose. This is why many people find it's easier just to limit foods with a lot of carbohydrate by following a low-carb diet.

More About the Glycemic Index, and Food Lists


Ebbeling, Cara, Leidig, Michael, Feldman, Henry, et al. "Effects of a Low–Glycemic Load vs Low-Fat Diet in Obese Young Adults." Journal of the American Medical Association. 297.19 (2007):2092-2102.

Selwin, Elizabeth, Coresh, Joseph, et al. "Glycemic Control and Coronary Heart Disease Risk in Persons With and Without Diabetes." Archives of Internal Medicine. 165/16 (2005)

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  5. Frequently Asked Questions
  6. How Do Low-Carb Diets Affect Blood Sugar

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