What Are Net Carbs?
Carbohydrates are our bodies' preferred source of energy, and most of us would feel pretty lousy if we didn't eat at least some of them. After a steady no-carb diet of only meats and fats, a platter of french toast, or even just an apple would get us salivating. But there is also a big difference between types of carbs in terms of the way they affect our bodies.
A bowl of salad, for example, will have a much different impact on blood sugar and energy than, say, a chocolate croissant. And for those on a strict low-carb diet like keto or Atkins, being aware of not only the quality of carb, but the number of carbs being consumed, becomes very important.
That's where net carbs come in. Of the three types of carbohydrates — starch, sugar, and fiber — starch and sugar are broken down by an enzyme in the small intestine into individual sugar units, which are then absorbed into the bloodstream. This is the case whether they are 'simple' carbohydrates, like those found in fruits, honey, and milk, or the 'complex' carbs found in whole grains and starchy vegetables (via Healthline).
Calculating net carbs can be helpful for low-carb diets
Fiber, on the other hand, behaves very differently. It can be either digestible or indigestible (also known as soluble or insoluble) but in either case, it is not absorbed by the small intestine, and passes through the digestive tract relatively unchanged. Since fiber is a carbohydrate but does not get absorbed by the body, many health experts believe it can just be 'subtracted' from your total carb count, resulting in the 'net carb' count. So, in the case of a medium-sized apple, you would calculate 25.13g (total carbs) – 4.4g (fiber) = 20.73 net carbs.
Lauren Harris-Pincus, M.S., R.D.N., author of The Protein-Packed Breakfast Club, explains "The idea behind net carbs is that all carbohydrates are not treated equally by the body. Since fiber is (mostly) indigestible, subtracting the fiber grams from total carbohydrates will provide the amount of 'net carbs' or the digestible amount of carbohydrate in the food" (via Men's Health).
Sugar alcohols like xylitol are carbs too, and mimic the role of fiber in the body. They are only partially absorbed in the small intestine, and can therefore have half of their carb count subtracted from the total carbs to calculate net carbs.