Figuring out how many carbs to eat when you have diabetes can seem confusing.

Dietary guidelines from around the globe traditionally recommend that you get around 45–60% of your daily calories from carbs if you have diabetes (1, 2).

However, a growing number of experts believe that people with diabetes should eat far fewer carbs. In fact, many recommend less than half of this amount.

This article tells you how many carbs you should eat if you have diabetes.

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Glucose, or blood sugar, is the main source of fuel for your body’s cells.

If you have either type 1 or type 2 diabetes, your ability to process and use blood sugar is impaired.

Type 1 diabetes

In type 1 diabetes, your pancreas is unable to produce insulin, a hormone that allows sugar from your bloodstream to enter your cells. Instead, insulin must be injected.

This disease is caused by an autoimmune process in which your body attacks its own insulin-producing cells, which are called beta cells. While usually diagnosed in children, it can start at any age — even in late adulthood (3).

Type 2 diabetes

Type 2 diabetes is more common, accounting for about 90% of diagnoses. Like type 1, it can develop in both adults and children. However, it isn't as common in children and typically occurs in people who are overweight or obese.

In this form of the disease, your pancreas either doesn’t produce enough insulin or your cells are resistant to insulin's effects. Therefore, too much sugar stays in your bloodstream.

Over time, your beta cells can degrade as a result of pumping out more and more insulin in an attempt to lower blood sugar. They can also become damaged from high levels of sugar in your blood (4).

Diabetes can be diagnosed by an elevated fasting blood sugar level or an elevated level of the marker HbA1c, which reflects blood sugar control over a period of two to three months (5).

Prediabetes

Before type 2 diabetes occurs, blood sugar levels are elevated but not high enough to be diagnosed as diabetes. This stage is known as prediabetes.

Prediabetes is diagnosed by a blood sugar level of 100–125 mg/dL (5.6–6.9 mmol/L) or an HbA1c level of 5.7–6.4% (5).

While not everyone with prediabetes develops type 2 diabetes, it's estimated that approximately 70% will eventually develop this condition (6).

What's more, even if prediabetes never progresses to diabetes, people with this condition may still be at an increased risk of heart disease, kidney disease, and other complications related to high blood sugar levels (6).

SUMMARY Type 1 diabetes develops from the destruction of pancreatic beta cells, while type 2 diabetes occurs from insufficient insulin or insulin resistance. Prediabetes often progresses to diabetes.

Many factors, including exercise, stress, and illness, affect your blood sugar levels.

That said, one of the largest factors is what you eat.

Of the three macronutrients — carbs, protein, and fat — carbs have the greatest effect on blood sugar. That’s because your body breaks down carbs into sugar, which enters your bloodstream.

This occurs with all carbs, such as refined sources like chips and cookies, as well as healthy types like fruits and vegetables.

However, whole foods contain fiber. Unlike starch and sugar, naturally occurring fiber does not raise blood sugar levels and may even slow this rise.

When people with diabetes eat foods high in digestible carbs, their blood sugar levels can surge. High carb intake typically requires high doses of insulin or diabetes medication to control blood sugar.

Because they’re unable to produce insulin, people with type 1 diabetes need to inject insulin several times a day, regardless of what they eat. However, eating fewer carbs can significantly reduce their mealtime insulin dosage.

SUMMARY Your body breaks down carbs into sugar, which enters your bloodstream. People with diabetes who eat a lot of carbs require insulin or medication to keep their blood sugar from rising too much.

Many studies support the use of carb restriction in people with diabetes.

Very low-carb, ketogenic diets

Very-low-carb diets typically induce mild to moderate ketosis, a state in which your body uses ketones and fat, rather than sugar, as its main energy sources.

Ketosis usually occurs at a daily intake of fewer than 50 or 30 grams of total or digestible carbs (total carbs minus fiber), respectively. This equates to no more than 10% of calories on a 2,000-calorie diet.

Very-low-carb, ketogenic diets have been prescribed for people with diabetes even before insulin was discovered in 1921 (7).

Several studies indicate that restricting carb intake to 20–50 grams of carbs per day can significantly reduce blood sugar levels, promote weight loss, and improve heart health in people with diabetes (8, 9, 10, 11, 12, 13, 14, 15, 16, 17).

In addition, these improvements often occur very quickly.

For instance, in a study in obese people with diabetes, limiting carbs to 21 grams per day for 2 weeks led to a spontaneous decrease in calorie intake, lower blood sugar levels, and a 75% increase in insulin sensitivity (16).

In a small, 3-month study, people consumed a calorie-restricted, low-fat diet or a low-carb diet containing up to 50 grams of carbs per day.

The low-carb group averaged a 0.6% decrease in HbA1c and lost over twice as much weight as the low-fat group. What’s more, 44% of them discontinued at least one diabetes medication, compared with 11% of the low-fat group (17).

In fact, in several studies, insulin and other diabetes medications have been reduced or discontinued due to improvements in blood sugar control (8, 10, 12, 13, 15, 17).

Diets containing 20–50 grams of carbs have also been shown to lower blood sugar levels and reduce the risk of disease in people with prediabetes (17, 18, 19).

In a small, 12-week study, obese men with prediabetes ate a Mediterranean diet limited to 30 grams of carbs per day. Their fasting blood sugar dropped to 90 mg/dL (5 mmol/L), on average, which is well within the normal range (19).

In addition, the men lost an impressive 32 pounds (14.5 kg), on average, and experienced significant reductions in triglycerides, cholesterol, and blood pressure, among other benefits (19).

Importantly, these men no longer met the criteria for metabolic syndrome due to reductions in blood sugar, weight, and other health markers.

Although concerns have been raised that higher protein intake on low-carb diets may lead to kidney problems, a recent 12-month study found that very-low-carb intake did not increase the risk of kidney disease (20).

Low-carb diets

Many low-carb diets restrict carbs to 50–100 grams, or 10–20% of calories, per day.

Although there are very few studies on carb restriction in people with type 1 diabetes, those that exist have reported impressive results (21, 22, 23).

In a long-term study in people with type 1 diabetes who restricted carbs to 70 grams per day, participants saw their HbA1c drop from 7.7% to 6.4%, on average. What’s more, their HbA1c levels remained the same 4 years later (22).

A 1.3% reduction in HbA1c is a significant change to maintain over several years, particularly in those with type 1 diabetes.

One of the biggest concerns for people with type 1 diabetes is hypoglycemia, or blood sugar that drops to dangerously low levels.

In a 12-month study, adults with type 1 diabetes who restricted daily carb intake to fewer than 90 grams had 82% fewer episodes of low blood sugar than before they started the diet (23).

People with type 2 diabetes may also benefit from limiting their daily carb intake (24, 25, 26).

In a small, 5-week study, men with type 2 diabetes who consumed a high-protein, high-fiber diet with 20% of its calories from carbs experienced a 29% reduction in fasting blood sugar, on average (25).

Moderate-carb diets

A more moderate-carb diet may provide 100–150 grams of digestible carbs, or 20–35% of calories, per day.

A few studies examining such diets have reported good results in people with diabetes (27, 28).

In a 12-month study in 259 people with type 2 diabetes, those who followed a Mediterranean diet providing 35% or fewer calories from carbs experienced a significant reduction in HbA1c — from 8.3% to 6.3% — on average (28).

Finding the right range

Research has confirmed that many levels of carb restriction effectively lower blood sugar levels.

Since carbs raise blood sugar, reducing them to any extent can help control your levels.

For instance, if you're currently consuming about 250 grams of carbs per day, reducing your intake to 150 grams should result in significantly lower blood sugar after meals.

That said, a severely restricted intake of 20–50 grams of carbs per day appears to produce the most dramatic results, going so far as to reduce or even eliminate the need for insulin or diabetes medication.

SUMMARY Studies demonstrate that restricting carbs may benefit people with diabetes. The lower your carb intake, the greater the impact on your blood sugar levels and other health markers.

Many tasty, nutritious, low-carb foods raise blood sugar levels only minimally. These foods can be enjoyed in moderate to liberal amounts on low-carb diets.

However, you should avoid the following high-carb items:

  • Breads, muffins, rolls, and bagels
  • Pasta, rice, corn, and other grains
  • Potatoes, sweet potatoes, yams, and taro
  • Legumes like peas, beans, and lentils (except green beans, snow peas, and peanuts)
  • Milk and sweetened yogurt
  • Most fruit, except for berries
  • Cakes, cookies, pies, ice cream, and other sweets
  • Snack foods like pretzels, chips, and popcorn
  • Juice, soda, sweetened iced tea, and other sugar-sweetened drinks
  • Beer

Keep in mind that not all of these foods are unhealthy. For example, fruits and legumes can be highly nutritious. Yet, they’re not optimal for anyone trying to manage their blood sugar levels by eating fewer carbs.

SUMMARY On a low-carb diet, you should avoid foods like beer, bread, potatoes, fruit, and sweets.

Low-carb diets have consistently been shown to lower blood sugar and improve other health markers in people with diabetes.

At the same time, certain higher-carb diets have been credited with similar effects.

For example, some studies suggest that low-fat vegan or vegetarian diets may lead to better blood sugar control and overall health (29, 30, 31, 32).

In a 12-week study, a brown-rice-based vegan diet containing 268 grams of carbs per day (72% of calories) lowered participants’ HbA1c levels more than a standard diabetes diet with 249 grams of total daily carbs (64% of calories) (32).

An analysis of 4 studies found that people with type 2 diabetes who followed a low-fat, macrobiotic diet consisting of 70% carbs achieved significant reductions in blood sugar and other health markers (33).

The Mediterranean diet likewise improves blood sugar control and provides other health benefits in individuals with diabetes (34, 35).

However, it's important to note that these diets weren’t directly compared with low-carb diets, but rather with standard, low-fat diets often used for diabetes management.

In addition, more research on these diets is needed.

SUMMARY Studies suggest that certain higher-carb diets may aid diabetes management. Still, research is needed.

Although studies have shown that many different levels of carb intake may help control blood sugar, the optimal amount varies by individual.

The American Diabetes Association (ADA) used to recommend that people with diabetes get around 45% of their calories from carbs.

However, the ADA now promotes an individualized approach in which your ideal carb intake should take into account your dietary preferences and metabolic goals (36).

It’s important to eat the number of carbs at which you feel best and can realistically maintain in the long term.

Therefore, figuring out how many carbs to eat requires some testing and evaluating to find out what works best for you.

To determine your ideal carb intake, measure your blood sugar with a blood glucose meter before a meal and again one to two hours after eating.

To prevent damage to blood vessels and nerves, the maximum level your blood sugar should reach is 139 mg/dL (8 mmol/L).

However, you may want to aim for an even lower ceiling.

To achieve your blood sugar goals, you may need to restrict your carb intake to less than 10 grams, 15 grams, or 25 grams per meal.

Also, you may find that your blood sugar rises more at certain times of the day, so your upper carb limit may be lower for dinner than for breakfast or lunch.

In general, the fewer carbs you consume, the less your blood sugar will rise and the less diabetes medication or insulin you'll require to stay within a healthy range.

If you take insulin or diabetes medication, it’s very important to speak to your healthcare provider before reducing your carb intake to assure appropriate dosage.

SUMMARY Determining the optimal carb intake for diabetes management requires testing your blood sugar and making adjustments as needed based on your response, including how you feel.

If you have diabetes, reducing your carb intake may be beneficial.

Multiple studies have shown that a daily carb intake of 20–150 grams, or 5–35% of calories, not only leads to better blood sugar control but may also promote weight loss and other health improvements.

However, some individuals can tolerate more carbs than others.

Testing your blood sugar and paying attention to how you feel at different carb intakes can help you find your own personal range for optimal diabetes control, energy levels, and quality of life.