Glycemic Load and Glycemic Index: What's the Difference and Why Does it Matter?

I was confused about the difference between these two systems so I spoke with registered dietitian Susan Weiner, who straightened me out.
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A few months ago I wrote about using the glycemic index (GI) ranking to manage weight and diabetes. Another measurement many use for weight and blood sugar management is Glycemic Load (GL). I was confused about the difference between these two systems so I spoke with registered dietitian and certified diabetes educator, Weiner, who straightened me out. This information may help you too.

(Editor's note: People with diabetes should speak to a qualified physician before starting a new diet.)

Q: What is glycemic load in very simple terms?

Susan Weiner: Glycemic load is a ranking system for carbohydrate-rich food that measures the amount of carbohydrates in a serving of food.

Foods with a glycemic load (GL) under 10 are considered low-GL foods and have little impact on your blood sugar; between 10 and 20 moderate-GL foods with moderate impact on blood sugar, and above 20 high-GL foods that tend to cause blood sugar spikes.

Q: How is glycemic load related to glycemic index?

SW: The glycemic index indicates how rapidly a carbohydrate is digested and released as glucose (sugar) into the blood stream. In other words, how quickly foods break down into sugar in your bloodstream. A food with a high GI raises blood sugar more than a food with a medium to low GI.

But the glycemic index does not take into account the amount of carbohydrate in a food. So glycemic load is a better indicator of how a carbohydrate food will affect blood sugar.

Here's a chart with carbohydrate foods' GL and GI

Q: If a food has a high glycemic index and a low glycemic load -- like graham crackers have a GI of 74 and a GL of 8.1 -- how will that affect your blood sugar?

SW: Food ranked high on the GI may represent a huge portion of a food because GI is not based on standard serving sizes. Basically, if a food is ranked high on the glycemic index it has readily available carbohydrate for quick absorption. However, the same food can have a low glycemic load because there may not actually be much total carbohydrate in a given serving of that food. A low GL is the better indicator that a food won't have much impact on blood glucose levels.

Here are two examples: Watermelon has a high GI of 72, yet a low GL of 7.21. The high GI is based on 5 cups of watermelon, not an actual serving size of 1 cup. The low GL means one serving of watermelon doesn't contain much carbohydrate, because it is actually mostly water. The low GL indicates that a serving of watermelon won't have much impact on your blood sugar.

Carrots are another example of a low GL food that many people think will raise their blood sugar a lot -- but it's not true. That's because carrots have a high GI of 71. However, what most people don't know, is that the GL for carrots is only 6. Therefore, unless you're going to eat a pound and a half of carrots in one sitting, an average serving of carrots will have very little impact on blood glucose levels. That said, juicing carrots -- which means consuming more carrots at once -- will have a greater impact on blood glucose.

Q: How can knowing the glycemic load and glycemic index of foods be used to make healthier eating choices?

SW: Everyone can benefit by eating a balanced diet of protein and fat, and foods that are lower on the GL and GI index. Foods with a lower GL and GI typically are high in fiber and nutrients and sustain your energy better throughout the day.

Also, knowing the GL of a food is a better indicator of whether that food will cause your blood sugar to spike. When your blood sugar spikes, the body releases extra insulin to bring down your blood sugar. If your body is asked to release extra insulin on a regular basis, it begins to lead to insulin resistance for many people and diabetes -- especially if diabetes is in your family.

Q: Can knowing the glycemic load of foods help people lose weight?

SW: Yes. Consuming low GL and GI foods keeps us satiated longer because these foods are more slowly broken down for glucose utilization. The result is that you feel fuller for longer.

When you consume high GL and GI foods, blood sugar levels spike which causes a short-term feeling of fullness, but then blood sugars plummet which causes you to crave food again and you ultimately end up consuming excess calories, which contributes to weight gain.

Q: If someone is trying to watch their weight, or has diabetes and wants to keep their blood sugar more stable, can you give us a sample low glycemic load menu?

SW: Here's a sample low GL menu:

2 egg omelet with ½ c. onions
Low-carb bread
1 tbs. almond butter

1 string cheese
Baby carrots

3oz. grilled chicken
1 ½ c. baby spinach
½ c. cucumber
½ c. beets
1 tbs. parmesan cheese
1 small apple

½ c. broccoli
1 tbs. light ranch dressing

3oz. salmon with mango, corn, cilantro salsa
6 spears of asparagus drizzled with extra virgin olive oil
8 oz. seltzer

4 oz. sugar-free pudding

Q: How seriously should we take all this?

SW: Some evidence suggests GL and GI diets can benefit overall health -- especially for people with diabetes, although, more conclusive research is needed to know for sure.

People who favor these rankings feel that GL and GI diets can help in the treatment and prevention of chronic diseases. Detractors note that selecting foods only by using GL and GI could cause people to choose bacon rinds over watermelon. I think we each have to decide for ourselves.

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