Net carbs are carbs minus fiber and sugar alcohols

Dear Doctors: I had lunch with a co-worker, and she’s on a keto diet. She says she can have only 35 grams of carbohydrates per day. The label on the candy bar she was eating said it had 26 grams of carbs, which is almost her whole carb budget. But she said it only had 6 net carbs. What does that mean?

The threshold to achieve and maintain ketogenesis is somewhere in the neighborhood of 50 or fewer grams of carbohydrates per day. However, everyone’s metabolism behaves differently, and some people find they need to restrict further than that. As a point of comparison for how those limits affect your daily diet, a medium-sized apple has 25 carbs. So does one Oreo cookie. It’s not surprising, with the rise in popularity of the keto diet, that a new food industry has arisen. It is devoted to serving low-carb needs while still slaking high-carb cravings.

And that (finally) leads us to net carbs and the candy bar your friend was eating. Net carbs refers to the amount of total carbohydrates in a food, minus the fiber content. Take that medium-sized apple we mentioned earlier. It has about 25 grams of carbs, and about 4.5 grams of fiber. Subtract the fiber, and you’re left with 21.5 net carbs. The thinking is that, because fiber doesn’t significantly affect blood-sugar levels, the grams of carbohydrates they it represents can be ignored.

Elizabeth Ko, MD and Eve Glazier, MD

The other type of carbohydrate that gets a free pass with net carbs is something known as sugar alcohols. Although portions of their structures resemble sugar and alcohol, they are neither. Rather, they are a type of carbohydrate that simulates sweetness. Because they don’t have a significant effect on blood sugar, they get deducted from total carbs. That’s how, once fiber content and sugar alcohols are accounted for, the 24 grams of carbs in your friend’s candy bar were magically reduced to 6 net carbs.

We think it's important to note that the FDA isn’t on board with the concept of net carbs. And while counting net carbs can expand the food choices of someone who is restricting sugars or carbs, they can also be an excuse to add sweets and snacks to the diet. Net carbs isn’t an exact formula. Rather than embrace this somewhat fuzzy science, we urge carb-conscious people to instead fill their plates with whole foods that are naturally high in fiber and low in sugar.

The UCLA Center for Human Nutrition is at the forefront of clinical practice and nutrition research. Learn more and schedule an appointment.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)


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