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Glycemic Index (GI)
The glycemic index (GI) is a numerical scale (from 0 to 100) that ranks carbohydrate-containing foods based on how quickly they raise blood glucose levels after consumption.
• Low GI (0–55): Foods that cause a slow and gradual rise in blood sugar.
• Example: Lentils, apples, and whole-grain bread.
• Medium GI (56–69): Foods that cause a moderate increase in blood sugar.
• Example: Brown rice, bananas, and sweet potatoes.
• High GI (70–100): Foods that cause a rapid spike in blood sugar.
• Example: White bread, sugary drinks, and baked potatoes.
Glycemic Load (GL)
The glycemic load (GL) takes into account both the GI of a food and the amount of carbohydrates in a serving. It provides a more accurate picture of a food’s impact on blood sugar levels.
• Low GL (0–10): Minimal impact on blood sugar.
• Example: Carrots (low-carb food with high GI but low GL).
• Medium GL (11–19): Moderate impact on blood sugar.
• Example: Basmati rice.
• High GL (20+): Significant impact on blood sugar.
• Example: White rice, sugary cereals.
Differences Between GI and GL
Aspect Glycemic Index (GI) Glycemic Load (GL)
Definition Measures how quickly carbs affect blood sugar. Combines GI with the amount of carbs in a serving.
Focus Speed of blood sugar rise. Total blood sugar impact per serving.
Calculation Based on 50g of carbs from the food. Accounts for actual portion size.
Practicality Less precise in real-world eating. More realistic and useful for meal planning.
Examples Watermelon (high GI but low carb). Watermelon (low GL due to small carb load).
Key Takeaway
• Use GI to understand how fast carbs affect your blood sugar.
• Use GL to assess the real impact of a food portion on your blood sugar.
For managing blood sugar, both measures are useful, but GL is generally more practical.
The glycemic load (GL) provides a more accurate picture of a food’s impact on blood sugar levels because it considers both the quality and quantity of carbohydrates consumed. Here’s why:
1. Incorporates Portion Size
• The glycemic index (GI) measures how fast a food raises blood sugar, but it is based on 50 grams of carbohydrates from that food, which may not reflect real-world portion sizes.
• GL, on the other hand, adjusts for actual serving size, giving a clearer picture of the total impact on blood sugar.
Example: Carrots
• GI: ~71 (high, based on 50g of carbs).
• GL: ~6 (low, because a typical serving of carrots has only ~10g of carbs).
Insight: Despite having a high GI, carrots have a low GL, meaning they’re unlikely to cause a significant blood sugar spike when consumed in normal amounts.
2. Reflects Total Carbohydrate Content
• GI only measures the speed at which carbohydrates convert to glucose. It ignores how much carbohydrate is actually present in a serving.
• GL accounts for the amount of carbs, showing the total glucose load on the body.
Example: Watermelon
• GI: ~80 (high).
• GL: ~5 (low, due to small carb content in a typical serving).
Insight: Foods with high GI but low carbohydrate density, like watermelon, have a low GL, making them less likely to cause large blood sugar spikes.
3. Practical for Meal Planning
• GL is more realistic for meal planning because it evaluates both quality (GI) and quantity (portion size) of food.
• GI alone can mislead by labeling foods as “bad” based solely on how quickly they spike blood sugar, even if the spike is minor due to low carb content.
Key Takeaway
• GI helps to identify how quickly foods raise blood sugar.
• GL tells you the actual blood sugar impact based on real portions, making it more accurate and practical for dietary decisions, especially for diabetics and those managing blood sugar levels.
Here are examples of foods where the glycemic index (GI) and glycemic load (GL) differ significantly due to portion size and carbohydrate content:
1. Watermelon
• GI: ~80 (High)
• GL: ~5 (Low, for a 120g serving)
• Reason: Watermelon has a high GI because its sugars are quickly absorbed, but it has low carbohydrate density, so the actual blood sugar impact per serving is small.
2. Carrots (Boiled)
• GI: ~71 (High)
• GL: ~6 (Low, for an 80g serving)
• Reason: Carrots have a high GI due to their natural sugars, but the total carbohydrate content per serving is very low, resulting in a low GL.
3. Pumpkin
• GI: ~75 (High)
• GL: ~3 (Low, for a 120g serving)
• Reason: Despite its high GI, pumpkin is mostly water and contains very few carbohydrates per serving, leading to a low GL.
4. Parsnips
• GI: ~85 (High)
• GL: ~4 (Low, for a 70g serving)
• Reason: Parsnips have a high GI due to fast-digesting carbs, but the small portion size typically consumed keeps the carbohydrate intake low.
5. Beetroot (Boiled)
• GI: ~65 (Medium)
• GL: ~5 (Low, for an 80g serving)
• Reason: Beets have a moderate GI but are low in total carbohydrates, so the GL is minimal when consumed in regular servings.
1. Cherries
• GI: ~62 (Medium)
• GL: ~6 (Low, for a 120g serving)
• Reason: Cherries have natural sugars that cause a moderate GI, but their low carbohydrate content keeps the GL low in typical servings.
2. Grapefruit
• GI: ~50 (Low)
• GL: ~4 (Low, for a 120g serving)
• Reason: Despite having a slightly higher GI than some fruits, grapefruit has low carb density, resulting in a very low GL per serving.
3. Peas (Green, Boiled)
• GI: ~51 (Low)
• GL: ~4 (Low, for an 80g serving)
• Reason: Green peas contain starch, which gives them a low GI, but their low carbohydrate content per serving ensures a minimal impact on blood sugar.
4. Sweet Corn (Boiled)
• GI: ~60 (Medium)
• GL: ~8 (Low, for an 80g serving)
• Reason: While sweet corn has a moderate GI, the actual carbohydrate amount in a serving is relatively low, so the GL remains manageable.
5. Hummus
• GI: ~28 (Low)
• GL: ~2 (Very Low, for a 30g serving)
• Reason: Hummus has a low GI due to its protein and fiber content, and its low carb density keeps the GL extremely low, even in larger portions.
Key Takeaway
These examples show that GL considers portion size, providing a more realistic measure of a food’s actual impact on blood sugar, unlike GI, which only evaluates how quickly glucose enters the bloodstream. Foods with high GI but low GL can often be eaten in moderation without causing significant blood sugar spikes.
