PRACTICAL PLATE

The way net carbs are calculated — total carbohydrate minus fiber and sugar alcohols — rests on one big assumption: that the fiber you’re subtracting passes through you completely, contributing no calories and no rise in blood sugar. Sometimes that’s true. Sometimes it very much isn’t.

If you’ve spent any time in the low-carb aisle, you’ve seen the magic trick. A tortilla with 22 grams of carbohydrate gets a big “4g NET CARBS” splashed across the front of the package. The other 18 grams? Fiber. And fiber, the logic goes, doesn’t count.

I count total carbs, not net. Not because I’m a purist, and not because a few grams of fiber is going to ruin your day — but because “net carbs” quietly assumes something that isn’t always true, and once you understand why, you’ll read those labels differently forever.

We’ve all seen this person. Maybe we’ve been this person. The cart is full of “low carb” everything — the bread, the sauces, the dips, the tortillas, the candy bars, the drinks — and on paper they’re doing everything right. But the blood sugar’s still high. The thing they went low-carb to fix is still sitting there, unfixed. It didn’t work, and it wasn’t a willpower problem. The science behind those “net carb” numbers was never really there.

Not all fiber does the same job

Here’s the piece that “net carbs” quietly ignores: fiber is a category, not a guarantee.

When the FDA finally wrote a definition of dietary fiber in 2016, it didn’t just say “carbs you can’t digest.” For the isolated fibers manufacturers add to foods, it said they have to be non-digestible carbohydrates that also have a proven, beneficial physiological effect — things like lowering blood glucose or cholesterol. They put that bar in place specifically so that not every isolated powder a manufacturer dumped into a product could be called fiber.

Why did they need that rule? Because fibers are wildly different from one another. They vary in chemical structure, in how their molecules are linked together, and in how long their chains are — and all of that changes how they behave in your body. Some fiber genuinely sails right through. Insoluble fiber, like the cellulose in vegetables and wheat bran, is largely inert and gets essentially zero calories on the label.

Other fibers — inulin from chicory root, resistant starches (more on this later) — aren’t digested by you, but get fermented by the bacteria in your gut, which can be a benefit, but that’s a different story than “it does nothing.” It’s still not the free pass the label implies.

But let’s talk about what started this whole post: ingredients marketed as fiber that your body actually digests.

“Net carbs” isn’t a real thing (officially, anyway)

On top of all that, the label term doing the subtracting isn’t even official. “Net carbs” is a marketing term, not a nutrition standard. The American Diabetes Association is blunt about it: the term has no legal definition, isn’t used by the FDA, and isn’t recognized by the ADA — and their recommendation is to use the total carbohydrate number on the label.

The only carbohydrate figures the FDA actually regulates on the Nutrition Facts panel are total carbohydrate, dietary fiber, and sugars. “Net,” “active,” and “impact” carbs live entirely outside that box, which means no one has checked the math on the front of the package.

The poster child: isomalto-oligosaccharide

If you want the clearest example of the net-carb game, look up isomalto-oligosaccharide. For years it was the darling of “low-carb” bars, syrups, and yes, tortillas, because it let manufacturers pile up fiber grams and shrink that net number.

The problem is that it doesn’t behave like fiber. In human trials, isomalto-oligosaccharide drives a blood sugar response on par with straight dextrose (glucose) — one study even measured it higher — the opposite of passing through undigested. A 2022 analysis went further and showed that human digestive enzymes fully break it down into glucose, just slowly, and concluded it had been “misjudged” as a fiber that bypasses the small intestine — largely because the older lab tests used to measure fiber couldn’t see what was actually happening.

An ingredient sold as fiber, subtracted as fiber to advertise a low net-carb number, is actually digested by your body into glucose — and that raises your blood sugar. If you were wearing a continuous glucose monitor, a “1g net carb” product built on it could spike you like a candy bar — and people have watched exactly that happen. That’s not a hypothetical loophole.

What about resistant starch?

Resistant starch is something people sometimes bring up to defend “net carbs.” It’s the most science-flavored argument in the whole net-carb world, so it’s worth taking seriously. It also doesn’t hold up the way people think.

Start with the claim you hear most: cook your potatoes, chill them, and the resistant starch means potato salad won’t spike you like a hot baked potato. The evidence there is mixed at best. Cooling forms only a modest amount of resistant starch — in one classic measurement it rose from about 7% to 13%, leaving most of the starch fully digestible — and the potato stays a high-glycemic food either way.

When researchers put it to the test in women with elevated blood sugar, chilled potatoes shaved a little off the early glucose bump and lowered insulin, but the total glucose response was no different than hot potatoes. Potato salad still spikes you. The “chill it and it stops counting” story is mostly wishful thinking, or perhaps confirmation bias.

Then there are the bigger promises — better insulin sensitivity, lower fasting glucose, weight and gut benefits. Human trials on those exist, but results are inconsistent across the different types and doses. Reviewers have even detected publication bias in the data — a sign the positive results are partly an artifact of which studies got published. It’s an ingredient with a lot of research and not much proven, reliable payoff — nothing like the settled science some labels imply.

And here’s why none of it rescues “net carbs” anyway: resistant starch isn’t a fixed number. How much of the starch in a food actually resists digestion depends on the variety, the ripeness, and how it was cooked and cooled — a green banana is loaded with it, and the same banana ripe has almost none. A label can’t keep up with that, so the grams being subtracted as “free” are an estimate at best.

So even with the fiber that has the most research behind it, net carbs is still guessing. Total carbs isn’t.

The texture tax

There’s a practical reason I’m not chasing these products anyway, beyond the numbers: they usually taste like the compromise they are.

To hit those inflated fiber counts, manufacturers lean on isolated, added fibers and modified wheat-starch derivatives — the stuff that lets them subtract big numbers. That’s exactly why so many “low-carb” tortillas come out gummy, rubbery, or weirdly tough, and why they crack when you fold them. You’re paying a texture tax for a number on the front of the bag, and often paying more money for the privilege.

I’d rather have a real white corn tortilla, smartly, strategically.

So what do I actually do with this?

I count total carbs. It’s the honest number, it’s the regulated number, and it never requires you to take a marketer’s word for it.

Learning to eat low-carb is complicated enough on its own — new meals, new swaps, figuring out what actually fills you up. You shouldn’t need a secret code for reading the label on top of all of it.

And here’s the good news, because I don’t want this to read as fear: you don’t need those products. A low-carb diet generally lands somewhere around 100–150 grams of total carbs a day, and real food fits inside that comfortably. Two eggs scrambled in butter, some cheese, and a couple of plain corn tortillas is about 23 grams of total carbs — no fiber accounting tricks required, and it actually holds you until lunch.

When a food is genuinely built from whole ingredients, you don’t have to squint at the fiber line and wonder how much of it is really going to hit your blood sugar. Total carbs already told you the truth.

That’s the whole philosophy of Practical Plate in one label: real numbers, real receipts, real food. No magic tricks, no hacks, and no math that isn’t supported by the actual research.

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Sources

• American Diabetes Association — Get to Know Carbs (on “net carbs” having no legal definition and not being recognized by the FDA or ADA): https://diabetes.org/food-nutrition/understanding-carbs/get-to-know-carbs
• U.S. FDA — Questions and Answers on Dietary Fiber (the 2016 regulatory definition and the beneficial-physiological-effect requirement): https://www.fda.gov/food/nutrition-food-labeling-and-critical-foods/questions-and-answers-dietary-fiber
• Gastrointestinal Effects and Tolerance of Nondigestible Carbohydrate Consumption (on the heterogeneity of dietary fibers): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9776669/
• Ingestion of isomalto-oligosaccharides stimulates insulin and incretin hormone secretion in healthy adults (isomalto-oligosaccharide produced a higher glycemic response than dextrose): https://www.sciencedirect.com/science/article/pii/S1756464619306541
• New insights suggest isomaltooligosaccharides are slowly digestible carbohydrates, rather than dietary fibers (2022; human enzymes fully hydrolyze it to glucose): https://pubmed.ncbi.nlm.nih.gov/35182873/
• Effects of resistant starch on glycemic control… in patients with metabolic syndrome and related disorders: a systematic review and meta-analysis of RCTs (significant reductions in fasting glucose and insulin): https://pubmed.ncbi.nlm.nih.gov/31661295/
• Effects of the resistant starch on glucose, insulin, insulin resistance… in overweight or obese adults: a systematic review and meta-analysis (describes the evidence as controversial): https://www.nature.com/articles/s41387-019-0086-9
• Gastrointestinal Tolerance and Glycemic Response of Isomaltooligosaccharides in Healthy Adults (glucose response not significantly different from dextrose, p = 0.662): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5872719/