Counting carbs: which number matters?

Q. I'm restricting my carb intake to lower my blood sugar levels and lose weight. What number should I use to track my daily carb intake? The number of carbs listed on the nutritional label? The number of net carbs (not exactly sure what that is)? The GI number? The GL number?

A.  Let me see if I can clear up the confusion about what all these numbers mean. Each number tells you something slightly different about the quality and quantity of carbohydrates in a food. You could choose any of them as your "marker." Each has pros and cons, which I'll outline below.

Total Carbohydrates, which is the number you'll find on the nutrition facts label, represents everything that's not protein, fat, or alcohol.  It includes starches, sugars, and fiber.  You can establish a target percentage for total carbohydrates, such as 40% of total calories, or a total number of grams, say, 150g. Your actual target number will depend on whether you're going for a moderate carb, low carb, or very low carb regimen.

One of the advantages of tracking total carbohydrates is that this number is almost always available, whereas a more detailed breakdown of carbohydrates is only sometimes given.  A potential weakness is that the number includes fiber, which is a nondigestible carbohydrates.  A high-fiber food might have more total carbohydrates than a low fiber food but still be lower in digestible (i.e. real) carbs.

Net Carbs refers to the digestible carbohydrates in a food. In most cases, this means the total carbohydrates minus the fiber. In some cases, sugar alcohols--which are a nondigestible form of sugar--are also subtracted from the total.  If you are tracking net carbs, as opposed to total carbs, your target will probably be slightly lower than if you are tracking total carbs.

Tracking net carbs is a slightly more refined version of tracking carbohydrates. One advantage is that it allows or even encourages you to eat more high-fiber foods because these don't blow your carb budget. Eating low net carb foods that are high in sugar alcohols, on the other hand, can lead to digestive distress.

Glycemic Index (GI) refers to a carbohydrate food's likely effect on your blood sugar.  For example, you could choose  to avoid foods with a high GI (70+), limit foods with a moderate GI (40-70), and focus on low GI foods (<40).  This will in effect shift your diet away from sweets and refined starches and toward whole grains, fruits, and vegetables.

The advantage of paying attention to GI is that it helps you to distinguish "good" carbs, which create a gradual and sustained increase in blood sugar, from "bad" carbs, which cause sharp increase in blood sugar. Some of the disadvantages of GI are that there is a limited number of foods for which the GI is known; the GI doesn't reflect serving size in any way (one carrot has the same GI as a hundred carrots); and there is a great deal of variation in how foods affect different people, so the GI may or may not predict how you will respond to a given food.  You can read more about the GI on our GI Topic page.

Glycemic Load (GL) is the GI multiplied by the amount of carbohydrates.  In other words, the GL of one hundred carrots is about a hundred times the GL of one carrot.  You can track the GL of individual foods but it's probably more helpful to look at the GL of whole meals. You might aim to keep the GL of each meal below 25 and the GL for the entire day below 100, for example.  Again, the actual numbers will depend on just how much you want to restrict carbs.

The advantage of glycemic load is that expresses both the quality of a carbohydrate (it's potential impact on blood sugar) as well as the quantity.  I think is a more useful and accurate indicator than the raw GI. The estimated Glycemic Load (eGL) here on NutritionData.com also makes GL figures available for any food and not just the limited number of foods that have been through GI testing. Read more about the eGL on our eGL Help Page.

Total Sugar is one more option that you didn't mention.  As sugar is the form of carbohydrate that has the most dramatic impact on blood sugar and can contribute to weight gain in the form of empty calories, many people simply choose to track and limit their sugar intake.  The World Health Organization recommends limiting added sugars (which do not include the natural sugars found in fruits and dairy products) to 10% of total calories, which is about 50g a day for a 2,000 calorie diet.

One advantage to limiting added sugars is that it focuses on the foods that offer least nutritionally and often do the most damage to health.  One disadvantage is that sugar is not always listed separately on nutrition facts labels.

What's a carb counter to do?

So, to return to your question: Which of these numbers does it make the most sense to track?  It really depends on your approach.  If you have embraced a hard-core, low-carb philosophy, then you're probably going to want to track total or net carbs.  If, on the other hand, you're simply looking for a way to monitor your diet and shift it toward healthier choices, I think tracking GL or total sugars can be quite useful. 

Also, take into account your personality. If you just want a quick and dirty way to keep tabs, I'd go with total carbs, which is readily available on every nutrition facts label. If you're trying to be more exact and are willing to do a little extra leg work, then net carbs and/or GL might be valuable.

Let me know what you decide and whether this was helpful!