Chalkboard reading CARBS surrounded by pasta, beans, bananas, berries, potatoes, rice, oats and bread

Carbs and Blood Sugar: What People With Diabetes Need to Know

Key Takeaways

  • Sugars and most starches are broken down into glucose, which circulates in the blood to be used as energy.[1]
  • The American Diabetes Association (ADA) says there is no ideal percentage of calories from carbohydrate.[2]
  • In a large review of adults without chronic disease, the risk reduction associated with a range of outcomes was greatest at 25 to 29 g (0.9 to 1 oz) of fibre a day.[3]
  • In 153 people without diabetes, glucose peaked about 97 minutes after eating on average.[4]
  • One carb choice is about 15 g (0.5 oz) of carbohydrate, and the ADA says there is "no magic number" per meal.[5]
  • If you take insulin or other diabetes medicines, ask your GP or primary care team before you cut carbs.[2]

Carbs and blood sugar are closely linked, because the body breaks sugars and most starches down into glucose, which then circulates in the blood.[1] The amount you eat, the type and the timing all shape how high your glucose climbs. This guide is general education. If you use insulin or other glucose medicines, follow the plan your diabetes team gave you.

How do carbs affect blood sugar?

Carbs raise blood sugar because the body turns them into glucose. MedlinePlus, from the US National Library of Medicine, says sugars and most starches are broken down into glucose, which circulates in the blood for energy.[1] Fibre is the exception, since the body does not break it down.[1]

The glycemic index (GI) ranks foods on a 100-point glucose scale, and 55 or below counts as low. The 2021 international tables list over 4,000 items. Dairy products, legumes, pasta and fruits were usually low GI. Cereals, including whole-grain versions, varied widely, probably because of how they are made.[6] Two of the authors are linked to the University of Sydney GI testing service.

Don't lean too hard on one GI number. A large Lancet review found smaller or no risk reductions for low GI diets in observational data, graded low to very low certainty.[3] It covered adults without chronic disease, so it can't speak directly for people with diabetes. Our post on smart nutrition choices has more.

What is the difference between simple and complex carbs?

Sugars are the simple carbs, and starches are the complex ones.[1] The simple or complex label is only part of the story. How processed a food is matters as much. The ADA advises minimally processed, high-fibre carbohydrate, with at least 14 g (0.5 oz) of fibre per 1,000 kcal.[2] It says to minimize refined grains and sweets.[2]

Grain choice shows up in the research. A meta-analysis of 16 cohort studies followed adults without diabetes. Eating 3 servings of whole grains a day was linked with a relative risk of 0.68 for type 2 diabetes. For refined grains it was 0.95, which was not significant.[7] These are associations, and they concern who develops diabetes, not glucose control in people who already have it.

Complex carbs vs simple carbs: five foods compared

Item. What the evidence says. Practical point.
White bread.[8] The USDA lists 49.4 g (1.74 oz) carbohydrate and 2.7 g (0.10 oz) fibre per 100 g (3.5 oz).[8] Refined grains are on the ADA list of foods to minimize.[2]
Whole-wheat bread.[8][6] The USDA lists 42.7 g (1.51 oz) carbohydrate and 6.0 g (0.21 oz) fibre per 100 g (3.5 oz).[8] Cereal products, including whole-grain versions, varied widely in GI.[6] Compare the fibre on the label rather than trusting the word "wholegrain".[8][6]
Rolled oats, dry.[8] The USDA lists 67.7 g (2.39 oz) carbohydrate and 10.1 g (0.36 oz) fibre per 100 g (3.5 oz) dry weight.[8] Dry oats are denser than a cooked bowl, so measure the portion.[8]
White rice, cooked.[8][7] The USDA lists 28.2 g (0.99 oz) carbohydrate and 0.4 g (0.01 oz) fibre per 100 g (3.5 oz).[8] White rice was linked with higher type 2 diabetes risk in cohorts.[7] Keep the portion modest and add fibre-rich foods to the plate.[2][8]
Lentils, cooked.[8][6] The USDA lists 20.1 g (0.71 oz) carbohydrate and 7.9 g (0.28 oz) fibre per 100 g (3.5 oz).[8] Legumes were usually low GI.[6] Lentils bring plenty of fibre along with their carbs.[8][6]

The NHS says starchy foods should make up just over a third of what you eat.[9] UK guidelines set a fibre target of 30 g (1.1 oz) a day, yet adults average about 20 g (0.7 oz).[10]

How many carbs should a person with diabetes eat?

There is no single right number. The ADA's 2026 Standards of Care say there is no ideal percentage of calories from carbohydrate, protein or fat for people with diabetes.[2] The same document says to consider reducing carbohydrate for some adults with diabetes to improve glycemia.[2]

How many carbs should a diabetic eat? It depends on you. The ADA's patient page also says there is no magic number per meal.[5] Your diabetes team can help you set a range that fits.

What low-carb trials show

Item. What the evidence says. Practical point.
ADA review of long trials.[2] Six trials of at least 12 months, with 524 adults with type 2 diabetes, found low-carb helped lipids but not glycemic management.[2] Long-term sustainability is a challenge.[2] Pick an approach you could keep up for years.[2]
BMJ 2021 meta-analysis.[11] Low-carb meant under 130 g (4.6 oz) a day. At 6 months, 57% on low-carb had an HbA1c under 6.5% (48 mmol/mol), against 31% on control diets, with medicines allowed.[11] Gains in weight and triglycerides faded by 12 months.[11] Early results are not a promise, and data beyond 12 months are sparse.[11]
Meta-analysis of 10 trials.[12] Diets under 45% of energy from carbohydrate were followed by an HbA1c difference of 0.34% (3.7 mmol/mol) in year one. At 1 year or later it was similar.[12] Any early gain may fade, so plan for the long term.[12]

The BMJ effect was smaller and not significant when no diabetes medicine was allowed. Cutting carbs can also change how much insulin or other medicine you need, so ask your GP or primary care team first. Our post on the HbA1c test explains the number these trials tracked.

How does carb counting work?

Carb counting means adding up the grams of carbohydrate in a meal. The ADA says one carb choice holds about 15 g (0.5 oz).[5] Carb counting for diabetes is a tool, not a rule.

The ADA's Standards list the plate method, carbohydrate choice and carbohydrate counting as meal planning tools.[2] Carb counting for diabetes follows three steps.

  1. Start with the carbohydrate line on food labels (in the US, Total Carbohydrate includes fibre, whereas on UK labels fibre is listed separately).[5][13]
  2. Weigh portions for a week or two until you can judge them by eye.[5][13]
  3. Use a meter or sensor to see how your own body responds. Our guide to self-monitoring covers the basics.[2][13]

For people with type 1 diabetes, counting links to insulin doses. The NHS says knowing how many carbs you eat and drink helps you manage your blood glucose and gives you more flexibility. It points to courses such as DAFNE (Dose Adjustment for Normal Eating).[13]

The DAFNE trial enrolled 169 adults with type 1 diabetes. At 6 months mean HbA1c was 8.4% (68 mmol/mol) after training and 9.4% (79 mmol/mol) in the waiting-list group. Severe hypoglycaemia stayed the same.[14] The trial was not blinded and dates from 2002.

How fast do carbs raise blood sugar?

In people without diabetes, glucose peaked about 97 minutes after a meal on average. In a study of 153 people wearing sensors, mean peak glucose per person rose from 93 mg/dL (5.2 mmol/L) before meals to 130 mg/dL (7.2 mmol/L).[4]

That group did not have diabetes and ate ordinary mixed meals. Your own peak may come later and climb higher. Stomach emptying plays a part. In 42 adults with type 1 diabetes, 36% had delayed emptying, which was associated with a longer time to peak glucose.[15] So timing varies from person to person. Checking your glucose before and after meals, as your team advises, shows your own curve.

What habits keep carbs and blood sugar steadier?

Swapping sugary drinks is a simple first step. The ADA advises replacing sugar-sweetened beverages, including any juices, with water or low-calorie or no-calorie drinks.[2] Regular cola has 10.4 g (0.37 oz) of carbohydrate per 100 g (3.5 oz), about 100 mL (3.4 fl oz), and no fibre.[8]

Build up fibre next. In the Lancet review of adults without chronic disease, the risk reduction associated with a range of outcomes was greatest at 25 to 29 g (0.9 to 1 oz) a day.[3] Staying active helps too, and our post on exercise and glucose has easy ways to start.

Pro Tip

Change one thing at a time. Swap one sugary drink for water this week. Next week, add a fibre-rich food such as lentils. Small steps are easier to keep.[2][3]

Do carbs and blood sugar need extra care with insulin or other medicines?

Yes. The ADA's Standards say alcohol can cause delayed hypoglycemia, particularly for people using insulin or insulin secretagogue therapies such as a sulfonylurea (for example gliclazide or glimepiride), so monitoring after drinking matters.[2] The same care applies when you change how many carbs you eat, because your doses may no longer match.

Don't change a dose on your own. Ask your GP or primary care team first. If your glucose drops, follow the plan your team gave you. Our post on low blood sugar covers the signs and recovery steps. Low blood sugar usually means below 4 mmol/L (72 mg/dL) in the UK or below 70 mg/dL (3.9 mmol/L) in the US.[16][17] In the UK, the NHS says to call 999 if someone may have very low blood sugar and is not responding normally or is unconscious, and a glucagon injection is not available or you do not know how to use it, or they have not recovered within 10 minutes of a glucagon injection, or they have been drinking alcohol.[16] In the US, the ADA says to call 911 right away if someone is unconscious and glucagon is not available or no one knows how to use it.[17] Do not give an unconscious person food or drink.[16]

Questions to ask your diabetes team

  • How many grams (or ounces) of carbohydrate per meal suit my daily routine and medicines?[2][5]
  • I use insulin or a sulfonylurea such as gliclazide or glimepiride. How should we adjust my doses before I reduce my carbohydrate intake?[2][16]
  • Would a structured education course such as DAFNE (for type 1) or dietitian support help me match my doses to my meals?[13][14][2]
  • What pre-meal and post-meal glucose readings should I aim for when testing how a new carbohydrate food affects me?[2][4]

Frequently asked questions

Do all carbs raise blood sugar?

Almost all of them do. Sugars and most starches are broken down into glucose, which circulates in the blood. Fibre is the exception, because the body does not break it down.[1]

How many carbs should I eat at each meal?

There is no magic number. The ADA says so on its carb counting page, and one carb choice holds about 15 g (0.5 oz) of carbohydrate. Its 2026 Standards add that there is no ideal percentage of calories from carbohydrate for people with diabetes.[5][2]

Do whole grains make a difference?

In cohort studies, yes for the risk of developing type 2 diabetes. Three whole-grain servings a day were linked with a relative risk of 0.68, against 0.95 for refined grains, which was not significant. These are associations, not proof.[7]

Is a low-carb diet right for everyone with diabetes?

No. The ADA suggests considering a reduction for some adults only. Its review of 6 trials of at least 12 months found a benefit for lipids but not glycemic management. Ask your GP or primary care team first if you take insulin or other diabetes medicines.[2]

Where to go next

For more on checking your numbers, tracking your average glucose and what is in our supplement, see:

Note: If you are pregnant, breastfeeding, or considering giving any supplement or herbal product to a child, consult your healthcare provider before making any changes to your diet, supplement routine, or prescribed medications.

Disclaimer: These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Talk to your doctor before changing your diet, your activity or your medicines, and before starting any supplement.

Sources & References

  1. MedlinePlus, US National Library of Medicine. Carbohydrates (accessed 23 October 2026). medlineplus.gov Funding: not applicable, this is official guidance, not a funded study.
  2. American Diabetes Association Professional Practice Committee for Diabetes. (2026). 5. Facilitating positive health behaviors and well-being to improve health outcomes: Standards of Care in Diabetes-2026. Diabetes Care, 49(Supplement_1), S89 to S131. pubmed.ncbi.nlm.nih.gov/41358898 Funding: none listed on the PubMed record. COI: Duality of interest information for each contributor is available at https://doi.org/10.2337/dc26-SDIS.
  3. Reynolds A, Mann J, Cummings J, Winter N, Mete E, Te Morenga L. (2019). Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. The Lancet, 393(10170), 434 to 445. pubmed.ncbi.nlm.nih.gov/30638909 Funding: none listed on the PubMed record. COI: no statement on the PubMed record.
  4. DuBose SN, Li Z, Sherr JL, Beck RW, Tamborlane WV, Shah VN. (2021). Effect of exercise and meals on continuous glucose monitor data in healthy individuals without diabetes. Journal of Diabetes Science and Technology. pubmed.ncbi.nlm.nih.gov/32064911 Funding: NIDDK NIH HHS; NCATS NIH HHS (grants listed on PubMed). COI: Declaration of Conflicting Interests: The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: SND, ZL, JLS, RWB, and WVT have no disclosures to report. VNS has received research grants and sits on the Advisory Board for Dexcom and Sanofi US.
  5. American Diabetes Association. Carb counting and diabetes (accessed 23 October 2026). diabetes.org Funding: not applicable, this is official guidance, not a funded study.
  6. Atkinson FS, Brand-Miller JC, Foster-Powell K, Buyken AE, Goletzke J. (2021). International tables of glycemic index and glycemic load values 2021: a systematic review. American Journal of Clinical Nutrition, 114(5), 1625 to 1632. Three authors co-wrote books on the glycemic index and receive royalties from them. Two of them oversee the University of Sydney glycemic index testing service and are non-executive directors of the Glycemic Index Foundation. The University of Sydney funded the study. pubmed.ncbi.nlm.nih.gov/34258626
  7. Aune D, Norat T, Romundstad P, Vatten LJ. (2013). Whole grain and refined grain consumption and the risk of type 2 diabetes: a systematic review and dose-response meta-analysis of cohort studies. European Journal of Epidemiology. pubmed.ncbi.nlm.nih.gov/24158434 Funding: none listed on the PubMed record. COI: no statement on the PubMed record.
  8. U.S. Department of Agriculture, Agricultural Research Service. FoodData Central (fdc.nal.usda.gov), SR Legacy, per 100 g (3.5 oz) (accessed 23 October 2026): FDC ID 174924 (white bread); FDC ID 172688 (whole-wheat bread); FDC ID 173904 (oats, dry); FDC ID 168878 (white rice, cooked); FDC ID 172421 (lentils, cooked); FDC ID 174852 (regular cola). Funding: not applicable, this is official guidance, not a funded study.
  9. NHS. Starchy foods and carbohydrates (accessed 23 October 2026). nhs.uk Funding: not applicable, this is official guidance, not a funded study.
  10. NHS. How to get more fibre into your diet (accessed 23 October 2026). nhs.uk Funding: not applicable, this is official guidance, not a funded study.
  11. Goldenberg JZ, Day A, Brinkworth GD, et al. (2021). Efficacy and safety of low and very low carbohydrate diets for type 2 diabetes remission: systematic review and meta-analysis of published and unpublished randomized trial data. BMJ. pubmed.ncbi.nlm.nih.gov/33441384 Funding: none listed on the PubMed record. COI: Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf and declare: support from Texas A&M University; BCJ receives funds from Texas A&M AgriLife Research to support investigator initiated research related to saturated and polyunsaturated fats for a separate research project, as part of his recent recruitment to Texas A&M University (support from Texas A&M AgriLife institutional funds are from interest and investment earnings, not a sponsoring organization, industry, or company); GB is author of the CSIRO Low Carb Diet Book that aims to translate clinical research outcomes of low carbohydrate diet studies for the general public in Australia, but he does not personally receive any financial royalties or funds either directly or indirectly from this publication, and any royalties received by his employment institution (CSIRO) do not contribute to his salary, nor have they been used to execute this work; no other relationships or activities that could appear to have influenced the submitted work.
  12. Snorgaard O, Poulsen GM, Andersen HK, Astrup A. (2017). Systematic review and meta-analysis of dietary carbohydrate restriction in patients with type 2 diabetes. BMJ Open Diabetes Research & Care. pubmed.ncbi.nlm.nih.gov/28316796 Funding: none listed on the PubMed record. COI: Competing interests: OS, GMP, and HKA report no competing interests. AA is a member of advisory boards/consultant for Lucozade Ribena Suntory, UK, McCain Foods Limited, USA, McDonald's, USA, NestlƩ Research Center, Switzerland, Swedish Dairy, and Weight Watchers, USA. Outside the present paper, research conducted at his department is often funded by grants from interests in the food and beverage sector. Recipient of honoraria as Associate Editor, American Journal of Clinical Nutrition, and membership of the Editorial Boards of Annals of Nutrition and Metabolism, and of Annual Review of Nutrition. Recipient of travel expenses and/or modest honoraria (under $2000) for lectures given at national and international meetings, often with support from one or more corporate sponsors. Cofounder and co-owner of the University of Copenhagen spin-out companys Mobile Fitness A/S & Flaxslim ApS, Denmark. Recipient of royalties form a number of textbooks, and popular diet and cookery books. Coinventor of a number of patents owned by UCPH, in accordance with Danish law.
  13. NHS. Living with type 1 diabetes (accessed 23 October 2026). nhs.uk Funding: not applicable, this is official guidance, not a funded study.
  14. DAFNE Study Group. (2002). Training in flexible, intensive insulin management to enable dietary freedom in people with type 1 diabetes: dose adjustment for normal eating (DAFNE) randomised controlled trial. BMJ. pubmed.ncbi.nlm.nih.gov/12364302 Funding: none listed on the PubMed record. COI: no statement on the PubMed record.
  15. Lupoli R, Creanza A, Griffo E, et al. (2018). Gastric emptying impacts the timing of meal glucose peak in subjects with uncomplicated type 1 diabetes. Journal of Clinical Endocrinology & Metabolism. pubmed.ncbi.nlm.nih.gov/29659867 Funding: none listed on the PubMed record. COI: no statement on the PubMed record.
  16. NHS. Low blood sugar (hypoglycaemia). Accessed 23 October 2026. nhs.uk Funding: not applicable, this is official guidance, not a funded study.
  17. American Diabetes Association. Hypoglycemia (low blood glucose): symptoms and treatment. Accessed 23 October 2026. diabetes.org Funding: not applicable, this is official guidance, not a funded study.
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