These rules lets you match your meal carbohydrates with insulin for better post-meal readings. However, carbohydrates are also needed to raise a low blood sugar. For this, there are two helpful guides:
One gram of carbohydrate raises the blood sugar about 3, 4, or 5 points for people who weigh 200 lbs., 150 lbs., and 100 lbs., respectively.
The glycemic index, protein content, and fat content of foods can modify the speed and strength of Guide 1.
Example of Guide 1: Say you weigh 150 lb. and your blood sugar is 60 mg/dl. You plan to eat a meal in a half hour, but you want to raise your blood sugar to 100 mg/dl to be safe during this time.
To get a 40 point rise (from your current reading of 60 mg/dl to your target of 100 mg/dl), you'll need 40 points / 4 points per gram, or 10 grams of carbohydrate. Two Becton Dickinson Glucose Tablets have 10 grams of carbohydrate and would put you close to your target.
Example of Guide 2: Say you want to eat 15 grams of carbohydrate to correct a low blood sugar. If you use a fast carb like glucose tablets (glycemic index = 100), relief will be apparent in 10 to 15 minutes. If instead you use a slow carb like kidney beans (glycemic index = 33), relief may not be apparent for 2 or 3 hours, assuming your blood sugar has not dropped further during that time. Obviously, using fast carbs to raise low blood sugars is better.