Why it's so important for people with diabetes to limit their carb intake

Stacy Lu

Jul 14, 2020, 22:37 IST

Why it's so important for people with diabetes to limit their carb intake

People with diabetes should eat complex carbs from foods like whole grains.Dunkin' Donuts

Experts recommend that people with diabetes get 45% of their daily calories from carbohydrates.
People with diabetes should consume more complex carbs from high-fiber foods than simple carbs like from fruit and milk.
Limiting carbs more than the recommended 45% of daily calories may provide even better results in controlling blood sugar levels.
This article was medically reviewed by Samantha Cassetty, MS, RD, nutrition and wellness expert with a private practice based in New York City.

People with diabetes have a complicated relationship with carbohydrates. While carbs are part of a healthy diet, they can also contribute to high blood sugar levels, which makes managing diabetes much more challenging. Many experts recommend that people with diabetes limit or even drastically reduce their carbohydrate intake.

Carbs drive blood sugar levels

Compared with proteins and fat, carbohydrates have the biggest impact on blood sugar levels, which is why keeping tabs on carb intake is so important for managing diabetes.

The digestive system breaks carbs down into glucose, or blood sugar, which is a main source of energy for the body. When sugar enters the blood, the pancreas usually releases the hormone insulin, which allows cells to process and absorb that sugar. As they do, blood sugar levels fall.

However, diabetes affects how people are able to produce or use insulin. In people with type 1 diabetes, their pancreas is unable to make insulin. People with type 2 diabetes can't make enough insulin, or their cells have stopped responding to it effectively, so glucose builds up in the blood.

In both types of diabetes, this can lead to dangerously high blood sugar levels if not treated. Consistently high blood sugar levels can damage blood vessels, eyes, feet, kidneys, and the heart.

Healthy carb intake for people with diabetes

The Centers for Disease Prevention and Control recommends that people with diabetes get about 45% of their daily calories from carbohydrates. Put another way, for a 2,000 calories diet that equates to about three or four servings of carbohydrates.

For those with diabetes, eating well is not just a matter of counting grams and calories, though. Choosing nutritious foods is key, says Jennifer Smith, Director of Lifestyle and Nutrition at Integrated Diabetes Services in Madison, Wisconsin.

There are two main types of carbs:

Complex carbohydrates, which are found in foods like potatoes, whole grains, and corn, provide nutrients and fiber which take longer to digest.
Simple carbohydrates, which are found in fruit and milk, and in refined foods such found in snacks, candy, soda, and desserts.

Simple carbs hit the bloodstream quickly and can lead to a higher spike in blood sugar levels compared to complex carbs.

"If you're doing 45% carbohydrates because that's what you've been told to do, but it's all white rice and white bread and Fruit Loops, that's not healthy," Smith says. "Simple sugars have a big impact on blood sugar, while more complex carbohydrates like grains, beans, and legumes have more fiber in them, which slows blood sugar impact once your body takes it into your system."

Lower-carb diets help stabilize blood sugar levels

While the 45% rule for total daily calories from carbohydrates is a general clinical guideline, there's evidence that eating fewer carbs has better results for controlling diabetes – and the fewer, the better.

The American Diabetes Association used to recommend that people eat at least 130 grams of carbs per day, but changed their position in 2019, saying that low-carb diets are a promising way to manage diabetes.

One way to do that is by following a low-carb, high-fat ketogenic diet, which is generally defined as eating no more than 50 grams of carbohydrates per day. When the body lacks carbs, you have less glucose in the blood for energy. To survive, your body enters a state called ketosis, where the body produce ketones that allow it to use fat as an alternate source of energy in place of glucose.

People on the ketogenic diet eat mainly meat, shellfish, eggs, nuts, salad, vegetables, and cheese. The key is to consume more fat than carbs so your body uses ketones for energy, which does not spike blood glucose levels.

The diet has had impressive results in research trials and in patients, says William Yancy, associate professor of medicine and director of the Duke Diet and Fitness Center at Duke University.

"Studies have shown that if you feed people food with a large fat content, it doesn't raise their blood sugar or insulin levels hardly at all. You can see from several studies that people's blood sugar improves to the point that they can cut back on their medicines. That's really rewarding to the individual. It's empowering for our patients," he says.

Smith says at least a third of her patients with diabetes aim to take in fewer than 120 grams of carbohydrates per day. "It can take out some of the up-down swings of blood sugar management, so mentally it's much less stressful for them."

However, it may be tough for some people to follow such a restrictive diet long-term."We've seen good health with much lower carb intake in many people. If you can stick with it, it will work. But we also have to work with what people are willing to do," Smith says.

There are some risks associated with following the ketogenic diet, including dehydration or a sudden and potentially dangerous drop in blood sugar levels. People with diabetes should follow a ketogenic only under the guidance of an experienced clinician, Yancy says.