Nutritionist - tell me about "Net Carbs" please

May 23, 2024 11:13 AM

Lately I am seeing this food label; "2gm Net Carbs" and then in smaller type; "14 gm Total Carbs - 12 gm Fiber = 2 gm Net Carbs." What does this mean in relation to glycemic index? Has this been the way carbs and fiber have worked forever? Is this some strange magic? Is this just a scam?
posted by leafwoman to Food & Drink (6 answers total)

Dietary fiber is (and always was) an indigestible type of carbohydrate.
posted by aubilenon at 11:22 AM on May 23 [6 favorites]

Fiber is a scientifically a carbohydrate, but your body cannot absorb it. So it has to be listed, legally, in the total carb count but the "net carbs" are the amount that your body can absorb and impact your blood chemistry.
posted by Huggiesbear at 11:27 AM on May 23 [3 favorites]

Your gut cannot directly absorb fibre, which is a form of carbohydrate. However, there are two types of fibre: insoluble, which is stuff that passes through you basically unchanged, and soluble, which forms a kind of gel in your gut. Insoluble fibre basically doesn't contribute any calories, while soluble fibre doesn't contribute any calories directly, but it is broken down by bacteria in your gut into energy that you can absorb. The net result for insoluble fibre is roughly half the caloric value of directly eating carbohydrates.

So if the fibre that is being subtracted is insoluble, then the net carbs figure is legit. If it's soluble, then it's a little more complicated. Soluble fibre is mostly broken down into short-chain fatty acids, which as the name suggests are not carbohydrates. So if you're looking at the label to see how many carbohydrates will directly be absorbed by your gut, then the net carbs figure is accurate. If you are looking to see how many calories you'll get from carbohydrates in total, including indirectly, then the number isn't really accurate.
posted by ssg at 11:27 AM on May 23 [3 favorites]

Just for some context, net carbs is often used by people who are following keto or other reduced carb diets which is why you are seeing it more and more often now.
posted by jacquilynne at 11:33 AM on May 23 [8 favorites]

I made a mistake in the comment above, it should read: "The net result for soluble fibre is roughly half the caloric value of directly eating carbohydrates."
posted by ssg at 11:34 AM on May 23 [2 favorites]

Yes to everything above! And just to build on what ssg says above, we think short-chain fatty acids (generally the result of soluble fiber broken down by gut bacteria) are extremely good for you. Thinking about them primarily as a result of the calories they "count" for would, in my estimation, be very misguided. They appear to nourish the gut microbiome and be preventative for colorectal cancer, among other good things. And as ssg says, the main reason that net carbs are listed is because of digestible carbohydrates' deleterious effect on insulin levels (raising them), which any kind of fiber is not going to do (and may well actually protect against; the jury is still somewhat out on the specifics, although see this recent interesting piece).
posted by ClaireBear at 8:44 PM on May 23 [1 favorite]