📘 Insulin-to-carbohydrate ratio

The insulin-to-carbohydrate ratio (ICR) tells you how many grams of carbohydrates one unit of rapid-acting insulin covers [1]. For example, a ratio of 10 means that one unit of insulin covers ten grams of carbohydrates. This ratio allows you to calculate more accurately how much insulin you need for a meal, regardless of its size. Thus, for 50g of carbohydrates with an ICR ratio of 10, you need 5 units (without correction).

The ratio varies greatly between individuals and in the same person at different times of the day [2]. Most patients need more insulin in the morning due to counter-regulatory hormones (or puberty hormones if applicable) [3]. Insulin requirement at lunch is generally 30-50% lower than in the morning. The correct ICR ratio brings your blood glucose back to the initial level two hours after the meal, without risk of hypoglycemia [4].

Count the total carbohydrates in the meal (by reading labels, weighing foods, using nutritional tables or apps), then divide by your insulin-to-carbohydrate ratio [1]. For 60g of carbohydrates with an ICR ratio of 12, you calculate 60 / 12 = 5 units. Round to the nearest half unit if using a pen or to 0.1 units with a pump.

Also consider your pre-meal blood glucose. If it's above your target, add a correction. If it's below target, reduce the dose slightly. Consider factors such as planned physical activity, fat and protein in the meal (may require extended bolus on pump) [5], alcohol consumed or another acute condition. Over time you will quickly estimate doses for meals, even without detailed calculations.

Start with reading labels. Look for "total carbohydrates" not "of which sugars" [6]. For foods without labels, weigh the portion and use nutritional tables or apps (MyFitnessPal, Foodvisor, Carbs&Cals). For homemade dishes, calculate carbohydrates from each ingredient and divide by the number of servings. Learn to visually estimate portions from frequently used foods.

Also pay attention to fiber. If it's over 5g, subtract half of it from total carbohydrates. For restaurants, many chains publish nutritional information online. Learn useful equivalences. For example, one slice of bread generally has 15g of carbohydrates, a cup of milk 12g, and a medium apple 20-25g. Accept that estimation won't be perfect [7]. Aim for ±10g accuracy for your regular meals [8].

Yes, it is normal and common for the ratio to differ throughout the day [2]. Most people need up to 50% more insulin per gram of carbohydrate at breakfast (dawn phenomenon, counter-regulatory hormones) [3]. The ICR ratio might be 8 in the morning, 12 at lunch and 10 in the evening. If meals are larger, some people need different ratios for simple versus complex carbohydrates [9].

To identify your ratios, systematically test blood glucose evolution after a meal. Eat a meal with known carbohydrates when starting blood glucose is on target and without other variables such as exercise or stress. Measure blood glucose at one hour and two hours after the meal for several days [4]. If they are above target, the ratio is too high. If you have hypoglycemia, it's too low. Adjust by two points and retest for several days.

The ratio is correct if blood glucose two hours after the meal returns to ±30 mg/dl (1.7 mmol/L) from the starting value, without hypoglycemia at three hours [4]. For more precise testing, start with blood glucose on target, eat a meal with well-calculated carbohydrates, without excessive fat or protein [5], avoid physical activity for the next four hours and don't make corrections in this interval.

Test each time of day separately, repeating the test at least three times for confirmation [10]. If blood glucose at two hours is consistently above 150 mg/dl (8.3 mmol/L), decrease the ratio by one point. If you tend to have hypoglycemia at two hours, increase the ratio. Document everything in a journal to see patterns. Don't test on atypical days (illness, major stress, menstruation).

The ratio can change over time for many reasons, such as weight changes (weight loss improves insulin sensitivity), level of physical activity (regular exercise increases sensitivity) [11], age (puberty decreases sensitivity), duration of diabetes (progressive loss of residual beta cells), concomitant medications and hormonal changes.

The season can also have an influence [12]. Some patients need less insulin in summer when they are more active. Chronic stress, illness or infections temporarily decrease insulin sensitivity. Pregnancy dramatically changes insulin requirement. Therefore, reevaluate ratios every three months or when you observe consistent patterns of postprandial hyper or hypoglycemia. Adjustments are a normal part of diabetes management.

MyFitnessPal has the largest food database, including many products and traditional dishes. Carbs&Cals offers photos with portions for visual estimation. Foodvisor uses AI for photo recognition [13]. You photograph the food and the app estimates carbohydrates. mySugr and Diabetes:M integrate carbohydrate counting with a diabetes journal and insulin bolus calculator.

For restaurants, fast-food chain apps have accurate nutritional information. Yuka scans barcodes and offers instant information. FatSecret has recipes with automatic calculation per serving. Most apps allow creating custom meals and recipes that you use frequently [14]. Choose the app that fits your style. Some prefer simplicity, others want advanced features.

Ideally, you weigh important foods for accuracy, especially in the beginning when learning portions [7]. After a few months, you will be able to visually estimate frequently used portions with acceptable error. Always weigh carbohydrate-dense foods such as bread, potatoes, pasta, rice, cereals [8]. For low-carbohydrate vegetables (under 5%), visual estimation is sufficient.

Invest in a digital kitchen scale. When eating out, use accumulated experience for estimation. Some people prefer to eat standard portions that they have memorized. Don't become obsessed with achieving perfect precision. An error of ±10g carbohydrates is acceptable for most meals [7].

Use experience with similar portions from home as reference [8]. Most restaurants serve standard portions. A slice of pizza has 30-40g, a burger 30-40g, a small portion of fries 25-30g. Ask for nutritional information at the restaurant. Many restaurants have them available. For complex dishes, mentally break down into ingredients and estimate each.

Apply the "better more than less" rule. Under-dosing insulin leads to prolonged hyperglycemia, overdosing is corrected more easily with fast carbohydrates. Photograph the food for future reference. Consider that restaurant food often has hidden sugars in sauces and dressings [7]. Measure blood glucose at two hours and adjust your estimation for next time when you eat something similar [4].

For complex dishes, break down into main ingredients and estimate carbohydrates from each [6]. For lasagna, you might consider pasta sheets + bechamel sauce + tomato sauce + cheese. Ignore ingredients with negligible carbohydrates (cheese, meat). For sauces, assume 10g carbohydrates per serving if they taste sweet. For cream soups, consider vegetables, flour and milk/cream. Fat and protein in complex dishes may require additional insulin [5].

Create a personal library of "recipes" in your app for frequent meals [14]. When cooking at home, calculate once for the entire pan and divide by servings. For pies or cakes, calculate total carbohydrates from flour, sugar, fruits and divide by number of slices. Over time, you will develop intuition for frequent combinations and won't calculate from scratch every time.