Low-carb diets like keto and Atkins have created an increased focus on carbohydrates. While carbs themselves aren’t inherently bad for you (kale, for instance, contains carbohydrates), these diets argue that too many of them is what can cause you to gain weight.
And that’s why many people who try these low-carb diets focus on reducing their carb intake. Some low-carb diets even have you calculate your “net carbs.” You may have even seen these words on keto-friendly foods at the supermarket.
The term “net carbs” simply means the amount of carbohydrates in a food that your body can digest and use for energy. “It’s essentially the amount of carbohydrate that will have an effect on blood sugar levels. These digestible carbs are sugars and starches,” says Charlotte Martin, M.S., R.D.N.
Your body converts these net carbs in two ways–stored as glycogen for energy or stored as fat. If your body needs energy in that moment–say, if you’re on a long-distance run and gulp down a gel pack–those carbs will replenish your glycogen stores.
If you’ve consumed too many net carbs and are inactive, those carbs will go toward your fat stores, which may be used for energy later. So where net carbs go after you’ve consumed them depends on your overall diet and activity levels.
So what about the carbs beyond net carbs?
“The idea behind net carbs is that all carbohydrates are not treated equally by the body,” says Lauren Harris-Pincus, M.S., R.D.N., author of The Protein-Packed Breakfast Club.
“Since fiber is (mostly) undigestible, subtracting the fiber grams from total carbohydrates will provide the amount of ‘net carbs’ or the digestible amount of carbohydrate in the food,” Harris-Pincus says. You can also subtract grams of sugar alcohols, glycerine and allulose, as they do not provide many calories but are counted in the total carbohydrate total on the label.
As for sugar alcohols in particular, these guys act somewhat like a fiber and are incompletely absorbed and metabolized by the body, so they have little effect on blood sugar levels (yet some do more so than others), adds Martin.
So … How Do You Calculate Net Carbs?
First, subtract all grams of fiber from the total grams of carbohydrates.
Then consider the sugar alcohols in the product, if any.
Absorption rates of sugar alcohols vary, and therefore some have more of an effect on blood sugar levels than others. “For example, the popular sugar alcohol erythritol has a negligible effect on blood sugar levels, and therefore doesn’t count towards net carbs,” says Martin. So, in that case, you’d subtract any grams of erythritol from the total carbohydrate count as well.
“To calculate net carbs for a product containing erythritol, simply subtract the grams fiber and erythritol from the number of total carbs. For example, a food product with 20 grams total carbs, 3 grams fiber, and 4 grams erythritol would contain 13 grams net carbs,” Martin says.
Of note: Some sugar alcohols do count towards net carbs. “Maltitol, sorbitol, isomalt, and glycerin contribute about half a gram carbs per gram. So, you would only subtract half of their amount from the sugar alcohol equation,” says Martin. “For example, if there were 4 grams of maltitol instead of erythritol in the above equation, you would only subtract 2,” she explains.
Most keto product manufacturers are aware that all of this is a lot of work and therefore use only erythritol in their products. The other sugar alcohols like maltitol might be found in sugar-free or reduced-sugar versions of candies, chocolates, and ice creams. Just check the labels.
What’s more, zero-calorie sweeteners like monk fruit and stevia do not contain carbs and therefore do not have an effect on blood sugar levels or contribute to net carbs, says Martin.
Why Is Calculating Net Carbs Important?
Calculating and tracking net carbs is important for those following the keto diet because consuming too many digestible carbs can prevent you from entering and/or kick you out of ketosis.
Your body’s preferred energy source is glucose (from carb-containing foods). When you drastically reduce your carb intake (like on the keto diet), your body is forced to start turning stored fat into ketones for fuel instead.
“The only other benefit I see to being aware of net carbs is that it forces you to be more aware of your fiber intake,” says Martin. In order to calculate net carbs, you have to look at the amount of fiber on the label. And fiber, as you know, is a power nutrient.
Easy ways to increase fiber intake include adding seeds (like chia or flax) to your morning oats or smoothie, adding avocados to your meals, snacking on raspberries, and swapping some animal proteins for plant ones (plant-based proteins, like legumes, are often rich in fiber).
Is Tracking Net Carbs Healthy?
Tracking net carbs typically isn’t necessary unless you’re following a keto diet.
“It could help with blood sugar management for those who need to control their blood sugar levels; however, it’s only one piece of the blood sugar response puzzle,” says Martin.
Calculating net carbs take into account the effects that protein and fat have on the blood sugar response. For instance, protein and fat help slow digestion and can therefore help lessen the blood sugar response if part of, or paired with a carb-containing food.
So it’s up to you. And a calculator.