Keto made easy

How to Read a Nutrition Label for Keto

Quick answer: Look at the serving size, then total carbohydrate. That's the most reliable carb number on a US label. The dietary fiber line doesn't tell you how much of the fiber your body can partly use, and sugar alcohols vary in how much they affect you, so "net carbs" (total minus fiber and sugar alcohols) is an estimate. Count total carbs when you're starting out or stalled, and check the ingredient list for hidden starches.

In this article

What the carb lines on a US label actually mean

Under the FDA's Nutrition Facts rules, "Total Carbohydrate" includes the dietary fiber. The "Dietary Fiber" line counts intact non-digestible plant carbohydrates plus isolated or synthetic ones the FDA has found beneficial (FDA, Questions and Answers on Dietary Fiber). Notice what's missing: the FDA page doesn't use the term "net carbs" at all. Net carbs is a keto-world calculation, not a label category.

Sugar alcohols (erythritol, maltitol and others) may also appear on the label. They're the other thing net-carb counting subtracts.

Why net carbs are a guess

KetoDick's explanation is the clearest version of the problem. US labels list dietary fiber as one number. They don't split it into soluble fiber, which he says partly digests and affects glucose, and insoluble fiber, which passes through without being digested (1vyxuWlxT5M). Without that split, you can't know how much of the fiber to subtract.

Sugar alcohols have the same problem. They vary in how digestible they are, and above certain amounts some will get an insulin response (ffwBPoKxlDI). Subtracting all of them assumes they all behave like the most inert one.

He showed a fiber-supplement label that does break down soluble and insoluble fiber, so it can be done; most American food labels just don't (1vyxuWlxT5M). See soluble vs insoluble fiber for what each type does.

How to read a label, step by step

  1. Check the serving size. Every number on the label is per serving. If you'll eat two, double everything.
  2. Read total carbohydrate first. That's the number you count when starting out or stalled. His 2018 beginner rule is 50 g of total carbs, partly for this reason (UygKGoP_BtA).
  3. Look at the dietary fiber line. A lot of fiber is a good sign about the food. Just don't assume all of it is free.
  4. Look for sugar alcohols. If the "net carb" claim depends on a big sugar-alcohol number, treat it with suspicion.
  5. Read the ingredient list. He singles out maltodextrin, a bulking agent with a high glycemic index, as a hidden carb to watch for (ffwBPoKxlDI). Sweet sauces, pasta sauces and drinks are other places he says carbs hide (carbs-hidden).
  6. Read protein as grams on the label. "100 g of protein" means 100 g as listed on labels, not 100 g of meat (cTGYIFOTPl8).
  7. Sanity-check with weight. An ounce is about 28 grams, so an ounce of food can't carry more than about 28 g of carbs. He uses that to take the fear out of a few chips at a party (xyEZL0HuejI).
  8. Decide: total or net. If you're new, stalled, or just want it simple, count total. If you're adapted and the fiber comes from real vegetables, a little discount is reasonable; he says he counts total but discounts avocados and green beans a little (xyEZL0HuejI).

A worked example

His example: a bar with 30 g of carbohydrate and 20 g of dietary fiber. You don't know if that's 20 g of insoluble fiber or 20 g of soluble fiber, so the carbs that count could be anywhere from 10 to 30 (ffwBPoKxlDI).

Reading Carbs counted Assumes
Net carbs (30 − 20) 10 g All 20 g of fiber does nothing
Total carbs 30 g All 20 g of fiber counts
Somewhere between 10–30 g What really happens, which the label can't tell you

Against a 20 g day, that bar is either half your budget or more than all of it. That's why he steers struggling people to total carbs: it removes the vague category from the count (ffwBPoKxlDI).

What the research says

The definitions back up the confusion. The National Academies separate "dietary fiber" (intrinsic and intact in plants) from "functional fiber" (isolated, with a physiological benefit) (NASEM, Dietary Reference Intakes, 2005). The international Codex definition calls dietary fibre carbohydrate polymers of 10 or more units that aren't broken down in the human small intestine, and leaves 3–9-unit carbohydrates to national authorities (Codex Alimentarius, CXG 2-1985). So what goes on the fiber line depends on whose definition you use, and none of these bodies defines "net carbs."

Here's where his account and the definitions differ. He describes soluble fiber as partly digested with a glycemic effect (1vyxuWlxT5M). The Codex definition says fibre isn't broken down in the small intestine, and a major review describes gut bacteria fermenting fiber into short-chain fatty acids (acetate, propionate and butyrate) (Koh et al., 2016), rather than it being digested like sugar. Both point the same practical way, though: the fiber line can't be treated as a clean subtraction.

There's no highly cited study on net-carb counting itself in the evidence pages, so there's no research number for how "wrong" net carbs are on average.

KetoDick's take

His bottom line on fiber-heavy foods is generous. If you're worried about counting a food's carbs because it has a lot of fiber, those are the right carbs to be eating (1vyxuWlxT5M). A cough drop has no fiber and no net-carb story to tell. A salad does.

If you use insulin and count carbs to dose it, don't change how you count (total versus net) without talking to your diabetes care team, since that number feeds directly into your dose.

Key takeaways