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This blog is purely informational and not meant to take the place of individual medical nutrition therapy (MNT). For serious medical conditions, ask your doctor for a referral to a dietitian. 

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Q: How do carbs affect blood sugar?

A: Carbs continue to cause confusion for many of the diet-conscious. Whether managing weight, blood sugar, or overall health, the topic of carbs can trigger anxiety in many people. Below are some key points to know about carbohydrates. Also included are images of how different types of foods affect blood sugar--and why it matters.

Carbohydrates include starch, sugar and fiber, which are found in the following types of food:

  • Legumes (such as beans and lentils) are an excellent source of plant protein, fiber, iron, calcium, and B vitamins.

  • Fruits and starchy vegetables are packed with phytonutrients like anthocyanins in blueberries, grapes and cherries; carotenoids in sweet potatoes and pumpkin; antioxidants like vitamin C in oranges. Along with fiber and other vitamins and minerals, these nutrients help the body fight disease.

  • Milk and yogurt contain a type of sugar called lactose. Dairy also provides calcium and potassium, which have been shown to help manage blood pressure. Dairy is also a good source of protein.

  • Whole grain versions of rice, quinoa, barley, farro, oats, wheat products, and other grains are good sources of fiber and B vitamins.

  • Other carbs like sweets, snacks and sugary beverages are tasty treats, but lack nutritional benefits.

Carbohydrates are one of the three major nutrients (macronutrients) in our foods. When carbs are digested, they break down into glucose (a.k.a sugar). Glucose is the primary fuel source for the brain and for exercising muscle.

The other macronutrients in food are fat, which digests into fatty acids, and protein, which digests into amino acids.

After digestion, glucose, along with other nutrients, enter the bloodstream and blood sugar rises (just like a car's fuel tank rises when you fill it with gas). The glucose travels to the cells of our muscle and organs and are either burned for energy or saved into storage. As we burn and store glucose, blood sugar levels go down.

Not all carbs are equal.

Simple sugars and refined grains are carbs that are quickly digested because they are low in fiber, fat and protein. They will break down into glucose and enter the blood stream quickly, causing a blood sugar spike. Examples of simple sugars include white or brown sugars, fruit juice and honey. Refined grains include white rice and white flour.

Carbs that are higher in fiber include fruit, starchy vegetables, beans, lentils and whole grains. Carbs that are higher in protein include milk, yogurt, beans and lentils. These types of carbs are digested more slowly, followed by a slower rise in blood sugar.

Balance matters.

The types of carbs we choose and how we balance them in a meal affect how blood sugar rises and falls after eating. The images below show how the impact of the type and combination of foods outweighs the effect of the amount of carbs.

The images below are taken from a continuous glucose monitor, a device that continuously records the rise and fall of blood sugar. I wore this device and tested how my blood sugar reacted to different types of meals. My results depicted the basic concepts of carbohydrate metabolism.

In the first picture, the data illustrates the sharp spike and fall that occurs after eating frosted cereal flakes, a combination of refined grains and simple sugar. After about 30 minutes, sugar level spiked to almost 200 mg/dL, then rapidly dropped soon after. Compare that to the breakfast smoothie made with oatmeal, a banana, low fat milk and peanut butter. With these ingredients, the smoothie is higher in fiber, fat and protein compared to the simple carbs of the cereal. Notice the lower rise of the blood sugar level. At 30 minutes, blood sugar peaked just over 150 mg/dL.

Of note, the amount of carbs in the cereal with milk is about 47 grams. The smoothie contains about 60 grams. Despite the higher amount of carbs in the smoothie, blood sugar did not rise as high.

47g carbs, <1g fiber, 10g protein, 2.5g fat

60g carbs, 7g fiber, 15g protein, 12g fat

Fat and protein also affect blood sugar.

The faster a food or meal is digested affects how quickly and how high blood sugar rises. Like fiber, both fat and protein slow digestion in the stomach. Thus, a high fiber carb combined with fat and protein will move down the digestive tract more slowly; the carbs will break down into glucose more slowly; and the glucose and other nutrients will enter the bloodstream more slowly, resulting in a slower, lower rise in blood sugar.

The image below shows the steady rise in blood sugar after eating gnocchi, or potato dumplings, combined with spinach, beets, pesto and walnuts. This meal contains about 75 grams of carbs from the potato. The walnuts and pesto add healthy fats. The nuts, spinach and beets provide fiber. The nuts, plus cheese in the dumplings, add protein to the meal. The graph below shows how the balance of carbs, fiber, fat and protein help provide a slow, steady flow of energy after the meal. Notice this meal has a higher amount of carbs than the previous examples.

75g carbs, 10g fiber, 25g protein, 46g fat

Why blood sugar matters.

Because glucose is an important fuel source for the body, the rise and fall in blood sugar affect our energy level, hunger, cravings, and food choices.

When blood sugar is low, we start to feel hunger signals. This is the signal to refuel.

Blood sugar spikes are often followed by rapid drops, which will cause us to feel hungry sooner. Drops in blood sugar can cause cravings for the types of foods that will bring our blood sugar up quickly, such as sweets and refined grains. These cravings lead to a vicious cycle of sugar spikes, drops and more cravings. This could lead to excessive snacking between meals, increased calorie intake, and excessive weight gain.

A slower, steadier rise in our blood sugar will help ward off hunger and cravings between meals. By managing blood sugar, we manage our hunger. If we can manage our hunger, we might better manage our food choices.

Spikes in blood sugar also cause spikes in insulin levels. Insulin is the hormone that helps our body convert glucose into energy. However, high insulin levels can promote weight gain. The combination of frequent spikes in insulin and weight gain can increase risk for type 2 diabetes.

So round out your meals! Check out these other posts for Ideas to add more protein to your meals

In my next post, I will answer the frequently asked question, "I have prediabetes. How do I turn it around?" If you are interested in learning more, please follow me for updates. If you know others who are interested in the complicated topic of health and nutrition, feel free to share this blog. There is more to come!


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