Educational

A protein bar advertising "3 g net carbs" can contain 25 grams of carbohydrate. The claim is legal, the arithmetic is documented on the packet, and the number that reaches your bloodstream is neither of those things.

Understanding how that gap gets manufactured makes this whole category readable.

How net carbs are calculated, and where it breaks

Net carbs means total carbohydrate minus fibre, and often minus sugar alcohols. For genuine fibre, the subtraction is sound — it isn't digested and doesn't raise blood glucose.

Two ingredients break the logic.

Sugar alcohols are not glucose-neutral. Erythritol is close, passing through largely unmetabolised. Maltitol is not — it has a glycemic index somewhere in the 35 to 52 range depending on the form, which is comparable to some whole foods. A bar sweetened with maltitol and marketed as low-carb is delivering meaningful carbohydrate that the net-carb figure subtracted entirely.

Isomalto-oligosaccharides, usually labelled IMO or "prebiotic fibre syrup," are the bigger problem. They're declared as fibre and counted as fibre, and independent testing has repeatedly found they're substantially digestible in humans, producing a real glucose response. A bar built on IMO syrup can behave like a bar built on sugar.

The way to read one of these labels is to ignore the net-carb claim entirely, look at total carbohydrate, and then check the ingredient list for maltitol and IMO. If either is prominent, treat the total as closer to the truth than the net.

What protein bars actually land at

Measured honestly, most mainstream protein bars carry a glycemic load somewhere between 10 and 20 — comparable to a slice of bread or a small bowl of cereal.

The ones built on dates, syrups and puffed rice are the highest. The ones built on nuts, seeds and whey with minimal binder are genuinely low, and they're identifiable in about five seconds from the ingredient list: whole ingredients you recognise, no syrup in the first three, no maltitol.

The category to be most careful with is bars marketed for diabetes or keto specifically, since those carry the strongest incentive to engineer the label rather than the food.

Powders are usually the simpler product

Plain protein powders are mostly straightforward, and unflavoured versions especially so.

Whey isolate is close to pure protein, with 1 to 2 g of carbohydrate per scoop. Whey concentrate carries a little more lactose, 3 to 5 g. Casein digests slowly, which makes it a reasonable evening option. Plant blends — pea, rice, hemp — usually run 3 to 8 g of carbohydrate and need blending to cover the amino acid profile properly.

Where powders get complicated is the additives: flavoured versions with added sugars, "mass gainer" formulations that are mostly maltodextrin, and meal-replacement shakes carrying 20 to 40 g of carbohydrate per serving.

Maltodextrin deserves a specific warning. It has a glycemic index around 85 to 105, which is at or above glucose itself, and it appears in a lot of products as a bulking agent and thickener.

The whey preload trick

One genuinely interesting finding: whey protein taken shortly before a meal reduces the glucose response to that meal.

Trials have measured meaningful reductions in postprandial glucose in people with type 2 diabetes when a small amount of whey was consumed 10 to 30 minutes beforehand. The mechanism combines slowed gastric emptying with a stimulated incretin response — the same effect that makes dairy insulinotropic.

It's a small effect with a plausible mechanism, similar in scale to eating vegetables first. Worth knowing if you already use whey; not worth buying it for.

Do you need any of it

Protein requirements are higher than the standard RDA for several groups: older adults, people doing resistance training, and people losing weight — particularly on a GLP-1, where preserving muscle becomes a live concern. Targets around 1.0 to 1.6 g per kilogram of body weight come up frequently in that literature.

Powders are a convenience for hitting those numbers, not a requirement. Greek yogurt, eggs, cottage cheese, milk, tinned fish and legumes deliver the same protein with fewer questions attached and generally cost less per gram.

Where powder genuinely helps is appetite. If you can't face another meal — common on a GLP-1, common when unwell, common after surgery — a shake gets protein in when food won't go.

A word on quality

Supplements aren't regulated to the standard of food or medicine, and independent testing has repeatedly found heavy metal contamination in protein powders, with plant-based products tending to test worse because plants take up what's in the soil.

Third-party certification programmes exist and are worth looking for on the tub. For daily use over years, that's a reasonable thing to care about.

Ready-to-drink shakes

The bottled shakes sold as meal replacements are their own category, and they split cleanly in two.

The high-protein, low-carbohydrate ones — typically 20 to 30 g of protein and under 5 g of carbohydrate — are a reasonable convenience product. The ones marketed for weight gain, recovery, or as general nutrition drinks frequently carry 30 to 45 g of carbohydrate, often as maltodextrin, and land at a glycemic load comparable to a dessert.

The nutritional drinks prescribed or recommended for older adults and people recovering from illness sit in that second group, which is deliberate — they're designed to deliver energy to someone who isn't eating enough. That's the right product for that job and the wrong one for a routine snack.

The short version

Ignore the net-carb claim. Read total carbohydrate, then check for maltitol and IMO. Prefer plain powders over flavoured ones and whole food over both.

And if a bar contains 20 g of carbohydrate, it's a snack with carbohydrate in it, which is fine — just not a free one, however the front of the wrapper describes it.