Glycemic Index and Type 1 Diabetes: What You Need to Know

Managing Type 1 Diabetes (T1D) as a family means learning a lot about food, insulin, and blood glucose (BG). One helpful tool is the glycemic index (GI). Knowing about the GI won’t replace carb counting or insulin dosing, but it can explain why blood sugars sometimes rise quickly and other times more slowly.

This guide is to help you understand the glycemic index and make food choices that support steadier blood sugar, energy, and confidence in managing T1D.

What is the Glycemic Index?

The glycemic index ranks carbohydrate foods by how fast they raise blood glucose:

• High GI Foods (70 or above): absorbed quickly -> fast spikes

• Medium GI Foods (56-69): moderate, steady rise

• Low GI foods (55 or below): slower absorption -> gradual rise

Carb Amount vs. Glycemic Index

It’s important to know that:

The amount of carbohydrate eaten has a larger effect on blood glucose than the GI of the food.

For example:

• A small portion of white rice (high GI) may raise BG less than a big portion of pasta (low GI), simply because the pasta has more total carbs

• Carb counting remains the main factor for working out insulin doses

GI is an extra layer of information- helping you understand the speed of BG changes, not the size of the rise alone.

Why is GI Useful for Families with T1D?

Insulin has to be injected or pumped, it doesn’t always match how fast or slow carbs are absorbed. Knowledge of the GI is useful for understanding how carbohydrate containing foods affect blood sugar levels.

• High GI Foods may raise BG before insulin is fully working -> spikes

• Low GI foods usually raise BG more gradually -> easier to stay in range

• Medium GI foods sit in between and can often be good for everyday meals

Examples of Foods by GI

High GI Food (fast spikes)

• White bread, bagels

• Cornflakes, Rice Krispies, Coco Pops

• White rice, jasmine rice

• Chips, fries

• Pretzels

• Watermelon, pineapple

• Cakes, biscuits, sweets, sugary drinks

Medium GI Foods (moderate rise)

• Wholemeal bread

• Weetabix

• Basmati rice

• Couscous

• New potatoes

• Sweetcorn

• Raisins, mango

• Ice cream

Low GI Foods (gentler rise)

• Seeded/ rye bread

• Porridge oats, muesli

• Pasta (al dente)

• Brown rice, quinoa

• Lentils, chickpeas, kidney beans

• Apples, pears, berries, cherries, oranges

• Carrots, sweet potato, broccoli

• Milk and yoghurt (unsweetened)

• Nuts and seeds

How Food Combinations Change GI

The GI of a single food changes when eaten as part of a meal:

• High GI + Low GI = medium overall effect

  • Example: White bread with peanut butter

• Protein, fibre, and fat slow digestion and reduce the GI effect

  • Example: An apple juice spikes BG quickly, but an apple with cheese raises it more slowly

GI is Just One Part of a Healthy Diet

• Carb quantity matters most for BG levels and insulin dosing

• GI shows how quickly those carbs act

• Other nutrients (protein, fibre, fat, vitamins, minerals) are essential for growth, development, and long-term health

Key Takeaways for Families

• Carb amount affects BG more than GI

• High GI = quick BG rise (useful for hypos or quick energy)

• Medium GI = steady rise, good for daily meals

• Low GI = gradual rise, good for daily meals

• Mixing food and including protein, fibre, and fat can lower the GI effect

• GI is one tool- not the full picture. Balanced nutrition is the goal.

Final Thought

Being GI aware can help children and teens with T1D feel more in control of their blood sugars, but it works best alongside carb counting, insulin timing, and a balanced diet.