Carbohydrates and Diabetes: How Carbs Affect Blood Sugar and What to Eat

Carbohydrates are often the first foods my patients worry about after being diagnosed with diabetes. They may be told to stop eating bread, rice, potatoes, fruit, or even beans. In most cases, that is neither necessary nor practical.

Carbohydrates usually have the greatest immediate effect on blood sugar after a meal, but the goal is not automatically to remove them. The more useful approach is to understand how much carbohydrate you eat, where it comes from, what you eat with it, and how your own blood sugar responds.

Written by: Dr. Albana Greca, MD, MMedSc, Family Physician and Medical Author

Medically reviewed by: Dr. Ruden Cakoni, MD, Endocrinologist

Last medically reviewed: July 2026

Quick Answer

People with diabetes do not need to eliminate all carbohydrates. Choose suitable portions of minimally processed, fiber-rich foods such as beans, lentils, whole grains, whole fruit, and starchy vegetables. Count total carbohydrate when needed, use the glycemic index only as a supporting guide, and compare meals with your glucose response. There is no single carb target that is right for everyone.

carbohydrates

What Are Carbohydrates?

Carbohydrates are one of the three main macronutrients, together with protein and fat. The body breaks down many carbohydrates into glucose, which cells use for energy. Carbohydrate foods can also provide fiber, vitamins, minerals, and beneficial plant compounds.

The three main types are:

  • Starches: found in bread, rice, pasta, oats, barley, potatoes, corn, peas, beans, lentils, and many other foods.
  • Sugars: including naturally occurring sugars in fruit and milk as well as added sugars in sweets, syrups, sweetened drinks, and many processed foods.
  • Fiber: the part of plant foods that is not fully digested. Fiber can support bowel, heart, and metabolic health and generally has much less direct effect on blood glucose than digestible starch or sugar.

The old division into “simple” and “complex” carbohydrates can be misleading. Whole fruit contains simple sugars but also fiber and nutrients. Some starchy foods, including certain breads, breakfast cereals, rice products, and potatoes, may raise glucose quickly. I prefer to judge a food by its portion, fiber, degree of processing, overall nutritional value, and personal glucose effect.

How Do Carbohydrates Affect Blood Sugar?

During digestion, sugars and many starches are broken down into glucose and absorbed into the bloodstream. Insulin then helps glucose enter cells. In diabetes, the body may not make enough insulin, may not use insulin effectively, or both. This is why carbohydrate-containing meals can produce a larger or more prolonged glucose rise.

The response is not determined by carbohydrate alone. It can also change with:

  • the portion and total grams of carbohydrate
  • the food’s fiber content and physical structure
  • processing, cooking, cooling, and ripeness
  • protein and fat eaten in the same meal
  • insulin or medication dose and timing
  • physical activity before or after the meal
  • sleep, stress, illness, hormones, and time of day
  • individual digestion and insulin sensitivity

This is also why the same food may not produce exactly the same glucose reading every time.

How Many Carbs Should a Person With Diabetes Eat?

There is no universal number of carbohydrates per meal or per day for every person with diabetes. Your needs depend on your diabetes type, age, body size, activity, medicines, insulin plan, pregnancy status, kidney or digestive health, weight goals, culture, food preferences, and glucose targets.

In carbohydrate-counting systems, one carbohydrate choice is approximately 15 grams of carbohydrate. This is a counting unit, not a recommendation that everyone should eat the same number of choices.

Some people benefit from eating a relatively consistent amount of carbohydrate at similar times. People who use rapid-acting mealtime insulin may match insulin to the carbohydrate they plan to eat using a ratio prescribed by their diabetes team. Other people may manage portions successfully with the plate method and may not need to count every gram.

My practical advice: Do not copy another person’s carb target. Start with your current eating pattern, measure the portions that most affect your glucose, and review your results with your doctor or registered dietitian.

How to Count Carbohydrates

Carb counting means adding the grams of carbohydrate in the foods and drinks you consume. It is especially important for people who use mealtime insulin, but it can also help other patients understand portions and after-meal readings.

For packaged foods

  1. Check the serving size.
  2. Find total carbohydrate, not only the sugar line.
  3. Compare the label serving with the amount you will actually eat.
  4. Multiply the carbohydrate grams if you eat more than one serving.

For example, if one serving contains 20 g of carbohydrate and you eat two servings, you have eaten approximately 40 g—not 20 g.

For foods without a label

Use a reliable food database, a dietitian-approved exchange list, or our carb counter calculator. Measuring cups or a food scale can be helpful while you learn the portions of rice, pasta, cereal, bread, fruit, and mixed dishes.

Total carbs, sugar, and net carbs

When counting for diabetes, begin with total carbohydrate. A food can contain little added sugar but still be high in starch and raise blood glucose. “Sugar-free” also does not mean carb-free.

“Net carbs” is a marketing term rather than a standardized diabetes dosing rule. Fiber and sugar alcohols vary in how they are digested and tolerated. If you use insulin, do not change your dose based only on a net-carb claim unless your diabetes team has taught you how to count that specific product.

Which Carbohydrates Are Better Choices?

I encourage foods that provide fiber and useful nutrients while limiting heavily refined products and large portions of added sugar. This does not turn any food into an unlimited food; portion size still matters.

Choose more often Why they can help Watch the portion
Beans, lentils, chickpeas Fiber, plant protein, minerals They still contain carbohydrate
Oats, barley, bulgur, quinoa, intact whole grains Often more fiber and less processing Cooked portions can become large
Whole fruit Fiber, vitamins, minerals, water Count the portion; juice is easier to overconsume
Plain milk or yogurt Protein, calcium, and other nutrients Check lactose and added sugar on the label
Potatoes, corn, peas, squash Nutrients and a practical meal option Treat them as the starch portion, not as unlimited vegetables

Foods to limit more often include sugar-sweetened drinks, large servings of fruit juice, candy, pastries, sweetened cereals, and large portions of highly refined bread, rice, pasta, chips, and similar snack foods. “Limit” does not always mean “never”; it means fit the food into a safe, realistic plan.

What Are Glycemic Index and Glycemic Load?

The glycemic index (GI) ranks carbohydrate foods by how quickly they raise blood glucose under standardized testing conditions:

  • Low GI: 55 or less
  • Medium GI: 56–69
  • High GI: 70 or more

GI does not tell you how much carbohydrate is in the portion you actually eat. Glycemic load (GL) combines GI with the amount of available carbohydrate in a serving. This can make GL more practical for comparing portions, but it is still an estimate.

GI and GL should support—not replace—carbohydrate counting, portion control, food quality, medication planning, and glucose monitoring. Values can vary by food variety, brand, ripeness, processing, cooking method, and meal combination. Breads, rice, cereals, and potatoes do not all share one GI value.

Acidic ingredients such as vinegar or lemon juice may slow the early glucose response to some mixed meals, but the effect is variable. They do not cancel the carbohydrate, replace medication, or make a large portion harmless. For a more detailed explanation, see my glycemic load chart and calculator.

Are There “Free” or Carb-Free Foods?

“Free food” is a meal-planning term, not a promise that a food has absolutely no effect. Some foods—such as plain meat, fish, eggs, and pure oils—contain little or no carbohydrate, although they may still provide calories, fat, sodium, or protein. Non-starchy vegetables usually contain small amounts of carbohydrate.

A product labeled “sugar-free” may still contain flour, starch, milk, fruit, or sugar alcohols. Always check the serving size and total carbohydrate. Several small servings can add up.

How to Build a Balanced Diabetes Plate

If you do not want to count every gram, the plate method is a practical starting point. On a roughly 9-inch plate:

  • fill half with non-starchy vegetables
  • fill one quarter with lean or plant protein
  • fill one quarter with a quality carbohydrate food
  • choose water or another unsweetened drink

Fruit or dairy may be added when it fits your personalized plan. Beans and lentils provide both carbohydrate and protein, so their place on the plate may depend on the rest of the meal.

You can find more meal-building ideas in my guide to the best foods for diabetes and the low-glycemic diet plan.

Learn From Your Personal Glucose Response

A glucose meter or continuous glucose monitor can help you connect a meal with what happened afterward. If your care team has asked you to monitor around meals, record:

  • your glucose before eating
  • the food, portion, and estimated total carbohydrate
  • medicine or insulin dose and timing
  • activity, illness, stress, or unusual circumstances
  • your glucose at the time recommended by your care team

One unusual result does not prove that a food is “bad.” Look for a repeated pattern. Our guides to blood sugar levels after eating and using a blood sugar log sheet can help you review the pattern more clearly.

Important Insulin and Medication Safety

Do not sharply reduce carbohydrates or skip meals without a safety plan if you use insulin or a medicine that can cause hypoglycemia.

Eating much less carbohydrate than expected can make your glucose fall too low. Your insulin-to-carb ratio, correction factor, meal timing, and dose must be prescribed or reviewed by your diabetes team. Never copy another person’s insulin ratio.

Alcohol also requires caution. It may contribute carbohydrate depending on the drink and mixer, but it can also increase the risk of delayed hypoglycemia, especially when combined with insulin or insulin-releasing tablets. Discuss alcohol with your clinician if you drink.

Doctor’s Note from Dr. Albana Greca

I do not want my patients to fear carbohydrates. I want them to recognize the portions that affect their glucose most, choose nutritious sources more often, and use their readings as feedback. A realistic plan that you can follow safely is more useful than a very strict plan that causes low blood sugar, poor nutrition, or repeated frustration.

Frequently Asked Questions

Should people with diabetes avoid all carbohydrates?

No. Most people can include suitable portions of nutrient-rich carbohydrate foods. The amount and timing should be personalized, especially if insulin or hypoglycemia-causing medicine is used.

Which carbohydrates are best for diabetes?

Beans, lentils, whole fruit, minimally processed whole grains, and suitable portions of starchy vegetables are often good choices because they provide fiber and nutrients. Your portion and glucose response still matter.

Should I count sugar or total carbohydrate?

Start with total carbohydrate. It includes sugar, starch, and fiber and is more useful than looking only at the sugar line when estimating a food’s carbohydrate content.

Can I eat bread, rice, pasta, or potatoes?

Usually yes, but portion, type, cooking method, and meal balance matter. Measure the serving, combine it with vegetables and protein, and review your glucose response.

Is fruit too high in sugar for diabetes?

Whole fruit can fit into many diabetes meal plans. It provides fiber and nutrients, but it still contains carbohydrate. Choose an appropriate portion and be more cautious with juice and large amounts of dried fruit.

Is glycemic index more important than carb amount?

No. GI can help compare foods, but it does not account for the amount you eat. Total carbohydrate, portion, meal composition, medication, activity, and personal response are usually more practical.

Related Questions

Related Resources

References

  1. American Diabetes Association Professional Practice Committee. Facilitating Positive Health Behaviors and Well-being: Standards of Care in Diabetes—2026.
  2. American Diabetes Association. Understanding Carbs.
  3. American Diabetes Association. How to Read Nutrition Labels: Carbs, Fiber, and Total Carbohydrates.
  4. Centers for Disease Control and Prevention. Carb Counting.
  5. National Institute of Diabetes and Digestive and Kidney Diseases. Healthy Living with Diabetes.
  6. Atkinson FS, Brand-Miller JC, Foster-Powell K, Buyken AE, Goletzke J. International Tables of Glycemic Index and Glycemic Load Values 2021: A Systematic Review.

Medical disclaimer: This page is for general education and does not replace personal medical advice, diagnosis, or treatment. Speak with your healthcare professional before changing your diet, insulin, diabetes medication, or glucose-monitoring plan.