Do Potatoes Raise Blood Sugar? UK Guide

Do potatoes raise blood sugar? Yes, as a starchy carbohydrate, potatoes are broken down into glucose relatively quickly, causing a rise in blood glucose levels. However, the extent of that rise depends on the variety chosen, how the potato is cooked, portion size, and what else is eaten alongside it. Understanding the glycaemic index and glycaemic load of different potato preparations can help people, particularly those with diabetes or prediabetes, make informed choices without needing to eliminate potatoes from their diet entirely.

Do potatoes raise blood sugar levels?

Yes, potatoes raise blood sugar because their starch is digested into glucose relatively quickly, though the rise varies by variety, cooking method, and portion size.

Yes, potatoes do raise blood sugar levels, because they are a starchy carbohydrate that the body breaks down into glucose relatively quickly. Potatoes are composed largely of starch, which is digested in the small intestine and absorbed as glucose into the bloodstream. This causes a rise in blood glucose, followed by an insulin response. The speed and magnitude of that rise depends on several factors, including the variety of potato, how it is prepared, and what else is eaten alongside it.

The glycaemic index (GI) is a scale from 0 to 100 that ranks how quickly a carbohydrate-containing food raises blood glucose compared with pure glucose.^[1][19] Many common potato preparations, such as baked or mashed white potatoes, tend to have a high GI, often above 70, though values vary considerably by variety, cooking method, and portion size.^[1][4] Diabetes UK and the University of Sydney GI database both note this variability, and GI figures should be treated as a guide rather than a fixed rule. Glycaemic load (GL), which accounts for the portion size actually consumed, is often a more practical measure for everyday eating.

For most healthy adults, moderate potato consumption as part of a balanced diet is unlikely to pose a significant concern, though individual responses vary depending on overall dietary pattern, activity level, and metabolic health. The NHS Eatwell Guide and Diabetes UK both acknowledge that starchy foods, including potatoes, can form part of a healthy diet, with portion size and preparation method mattering considerably.^[2][3] Potatoes are also a useful source of potassium, vitamin C, and dietary fibre (particularly when eaten with the skin on), according to the British Nutrition Foundation, so they need not be excluded entirely from a health-conscious diet. People on potassium-restricted diets, for example those with chronic kidney disease, should follow the specific advice of their clinician or dietitian regarding potato intake.

Why do some potatoes affect blood sugar more than others?

Varieties higher in amylopectin, such as floury types like Maris Piper, are digested faster and raise blood sugar more than waxy varieties with higher amylose content, such as Charlotte.

Different potato varieties affect blood sugar differently because they contain varying proportions of two types of starch: amylose and amylopectin. Amylopectin is a branched starch that is digested rapidly, leading to a faster and higher blood glucose rise. Amylose is a more linear starch that is digested more slowly, producing a more gradual glucose response. Varieties with a higher amylose content therefore tend to have a lower glycaemic index, though cooking method has a strong and sometimes overriding influence on the final GI of any variety.

Floury or mealy potato varieties, such as King Edward or Maris Piper, tend to have a higher GI because their starch granules break apart easily during cooking, making them more accessible to digestive enzymes. Waxy varieties, such as Charlotte or Jersey Royals, generally retain their structure better after cooking and tend to have a somewhat lower GI, though they remain a source of digestible carbohydrate and the difference between varieties can be modest. The University of Sydney GI database and the BDA Food Fact Sheet on glycaemic index provide further detail on variability by variety and preparation.

The size of the potato also matters in practical terms. A large baked potato can contain considerably more carbohydrate than a small boiled new potato, meaning the glycaemic load, and therefore the actual blood glucose impact, can be substantially higher even if the GI of the variety is similar. Eating potatoes as part of a mixed meal that includes protein, healthy fats, and non-starchy vegetables further slows gastric emptying and reduces the overall glycaemic response.

Leaving the skin on where possible is a straightforward way to preserve the fibre content of a potato, which can modestly slow digestion and moderate the glucose rise. Peeling potatoes before cooking removes this benefit, though the overall effect of the skin on GI is modest and should not be overstated.

How cooking and cooling methods change a potato's glycaemic impact

Boiling and steaming produce a lower GI than baking or mashing, and cooling cooked potatoes in the fridge converts starch to resistant starch, meaningfully reducing their glycaemic impact.

The way a potato is cooked has a significant effect on how quickly it raises blood sugar, because heat and moisture alter the physical structure of starch granules in a process called gelatinisation. When starch gelatinises, it becomes more accessible to digestive enzymes, which speeds up glucose absorption. Evidence from the University of Sydney GI database and published nutrition research suggests that boiling and steaming tend to produce a lower GI than baking or roasting, partly because the potato retains more moisture and the starch structure remains somewhat more intact.^[9][10]

Mashing potatoes substantially increases their GI because the physical disruption of the cells exposes starch to digestion very rapidly.^[4][6] Roasting and baking at high temperatures also produce a high GI. Frying, as in chips or crisps, adds significant calories and fat (the type of fat depends on the oil used), and is often high in salt; these factors bring additional health considerations beyond blood glucose alone.

One well-documented way to reduce the glycaemic impact of potatoes is to cook and then cool them before eating. Cooling cooked potatoes in the refrigerator for several hours converts a proportion of the digestible starch into resistant starch, a form that passes through the small intestine largely undigested and acts more like dietary fibre. Peer-reviewed research has demonstrated that this process meaningfully lowers the GI of potatoes, and that reheating cooled potatoes does not fully reverse this conversion. Cold potato salad or reheated boiled potatoes that were first cooled therefore retain a lower GI than freshly cooked equivalents. This is a practical and accessible strategy for people managing blood glucose.

For food safety, cooked potatoes should be cooled quickly (within one to two hours), stored in the refrigerator, and reheated thoroughly until piping hot before eating. NHS and Food Standards Agency guidance on safe cooling and reheating of cooked foods applies here as with any cooked starchy food.

Which types of potato are safer if you have diabetes or prediabetes?

Waxy varieties such as Charlotte, Nicola, and Jersey Royals, served boiled or cold, are generally better choices for people with diabetes due to their lower glycaemic index.

Waxy potato varieties tend to be a better choice for people with diabetes or non-diabetic hyperglycaemia (prediabetes), because their lower GI generally produces a more gradual rise in blood glucose compared with floury varieties, though portion size and meal composition remain equally important. Examples of waxy varieties commonly available in the UK include Charlotte, Nicola, Jersey Royals, and Anya. These varieties hold their shape well after boiling and are well suited to salads, where they can be served cold to further reduce their glycaemic impact through resistant starch formation.

Sweet potatoes are often cited as a lower-GI alternative to white potatoes, and when boiled, they do tend to have a lower GI according to published GI databases. However, baking sweet potatoes raises their GI considerably, so preparation method remains important regardless of variety. Sweet potatoes are not dramatically lower in carbohydrate than white potatoes, so portion size still matters.

For people managing type 2 diabetes, Diabetes UK recommends focusing on portion control, preparation method, and the overall composition of the meal rather than avoiding potatoes entirely. A small portion of boiled new potatoes served with a source of protein, such as grilled fish or chicken, alongside non-starchy vegetables, is a nutritionally balanced option that limits the glycaemic impact. People with diabetes who are uncertain about how specific foods affect their individual blood glucose levels may benefit from self-monitoring of blood glucose before and approximately two hours after eating, in line with their individual care plan; NICE NG28 and Diabetes UK guidance on blood glucose targets provide further context on monitoring.^[14][15]

Importantly, people who use insulin or sulfonylureas (such as gliclazide or glipizide) should seek advice from their diabetes team or GP before making significant changes to their carbohydrate intake, as reducing carbohydrates without adjusting medication can increase the risk of hypoglycaemia (low blood sugar).

Anyone with newly diagnosed diabetes or non-diabetic hyperglycaemia (prediabetes) should seek dietary guidance from their GP or a registered dietitian, as individual responses to carbohydrate vary. If you experience persistent high blood glucose readings, or symptoms such as excessive thirst, frequent urination, or feeling unwell, contact your GP or diabetes team promptly.

How to include potatoes in a balanced, blood sugar-friendly diet

Choose waxy varieties, boil or steam rather than bake or fry, control portions, and pair potatoes with protein and non-starchy vegetables to moderate the blood glucose response.

Potatoes can be included in a blood sugar-friendly diet by applying a combination of practical strategies around variety, portion size, preparation, and meal composition. The key principles are straightforward and do not require eliminating potatoes altogether, which is neither necessary nor supported by current NHS or Diabetes UK guidance.

Useful strategies include:

• Choose waxy varieties such as Charlotte or new potatoes where possible, and leave the skin on to preserve fibre content.

• Boil or steam rather than bake, roast or fry, as these methods tend to produce a lower GI.

• Cook, cool, and reheat potatoes to increase resistant starch content and lower the glycaemic response.

• Control portion size: Diabetes UK and the BDA suggest using a hand-based or plate-model approach as a practical guide; as an illustrative example, a portion of around 150 to 180 grams of cooked potato is often cited, though individual needs vary and your dietitian or diabetes team can advise on what is right for you.

• Balance the plate: pair potatoes with non-starchy vegetables, a lean protein source, and a small amount of healthy fat to slow digestion and moderate the blood glucose rise.

• Avoid high-fat additions such as large amounts of butter, cream, or full-fat cheese, which add calories without reducing glycaemic impact meaningfully.

People who use insulin or sulfonylureas should consult their diabetes team before making significant changes to their carbohydrate intake, to avoid the risk of hypoglycaemia. If you experience persistent high blood glucose readings or feel unwell, contact your GP or diabetes team.

For people with type 2 diabetes or non-diabetic hyperglycaemia (prediabetes) who are considering broader changes to their diet or weight management, a consultation with a healthcare professional is an important first step. Bolt Pharmacy is a GPhC-registered UK online pharmacy offering online weight-management consultations, with prescriber review and pharmacist support, for those exploring clinically supervised options alongside dietary changes. Ultimately, no single food determines blood glucose control: overall dietary pattern, physical activity, and any prescribed medication work together. If you are concerned about your blood sugar levels or how your diet is affecting them, speak to your GP, who can arrange appropriate testing and refer you to a dietitian if needed.

Scientific References

1. Glycaemic index and diabetes.
2. Starchy foods and carbohydrates.
3. The Eatwell Guide.
4. Protein and fat modify the glycaemic and insulinaemic responses to a mashed potato-based meal.
5. Glycaemic index values for commercially available potatoes in Great Britain.
6. Glycaemic and satiating properties of potato products.
7. Predicting mixed-meal measured glycaemic index in healthy subjects.
8. The effects of potatoes and other carbohydrate side dishes consumed with meat on food intake, glycemia and satiety response in children.
9. Lower nocturnal blood glucose response to a potato-based mixed evening meal compared to rice in individuals with type 2 diabetes.
10. Chilled Potatoes Decrease Postprandial Glucose, Insulin, and Glucose-dependent Insulinotropic Peptide Compared to Boiled Potatoes in Females with Elevated Fasting Glucose and Insulin.
11. Relationship between Processing Method and the Glycemic Indices of Ten Sweet Potato (Ipomoea batatas) Cultivars Commonly Consumed in Jamaica.
12. Food processing methods influence the glycaemic indices of some commonly eaten West Indian carbohydrate-rich foods.
13. Type 2 diabetes – British Dietetic Association.
14. Type 2 diabetes in adults: management (NG28).
15. Blood glucose management – Type 2 diabetes in adults (NG28).
16. Adapting Medication for Type 2 Diabetes to a Low Carbohydrate Diet.
17. Cooking your food.
18. Children's food: safety and hygiene.
19. Evaluation, influencing mechanisms, regulatory strategies, and industrial standardization of glycemic index in starchy foods: An integrative framework based on starch digestion.

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