Case Study 2 — The Fiber Aisle: Where 6 Grams Costs More Than 15

A market and label case. The products are composites of real categories; the label mechanics and the regulatory situation are not.

Setup

Fiber is the one nutrient in this book where the cheapest source is also the best source, and the supermarket has responded to that inconvenient fact with remarkable creativity.

I costed everything in a large supermarket making a fiber claim, plus the plain foods that don't make one, and converted all of it to cost per 10 g of fiber.

The spread is roughly twenty-five-fold, and it runs in exactly the direction you'd predict.

The shelf

Twelve cents to four dollars for the same ten grams.

Three things the table shows

1. The claim-bearing products are the worst value

Every product making a fiber claim on the front sits in the bottom half of the table. Every product at the top makes no claim at all, because split peas have no marketing department.

This is §11.11's "zero for seven" made physical: the products that advertise fiber are the ones that had to add it, and adding it costs money that plain lentils never spent.

2. "Added fibre" is usually one specific ingredient

Look at the fiber-source column for the bottom five products. Four of them say some version of chicory root fibre / inulin / oligofructose.

That's not an accident. Inulin is cheap, near-tasteless, dissolves easily, adds bulk, and counts toward the fiber number on the label. It is the additive of choice for making a refined product qualify for a fiber claim.

Is it fiber? Yes, genuinely — it's fermentable, it's a legitimate prebiotic, and it does feed colonic bacteria.

Is it the same as eating lentils? No, and for two reasons. First, it's a single highly fermentable fiber rather than a mixture — which is why "high fibre" bars are notorious for producing gas, and why people who react badly to one often conclude that fiber in general disagrees with them (§11.8's failure mode, manufactured at scale). Second, it arrives without any of the food matrix — no protein, no potassium, no folate, no magnesium, no polyphenols, no displacement of anything else. It's Chapter 2's whole-food fallacy sold by the box.

3. The added sugar column tracks the fiber claim

Read the last two columns together. The products with the strongest fiber claims carry the most added sugar. The "digestive health" drink delivers 4 g of fiber and 8–12 g of added sugar. The snack bar delivers 6 g of fiber alongside 6–9 g of sugar plus polyols (Chapter 7 §7.11).

A fiber claim is a claim about one number, and it is silent on everything else — which is Chapter 8's protein-claim lesson, arriving with a different nutrient.

The label mechanics

Three things worth knowing before you read a front-of-pack fiber claim.

"Source of fibre" and "high in fibre" are regulated claims with defined thresholds, and the thresholds are lower than people assume — commonly around 3 g per 100 g for "source" and 6 g per 100 g for "high," with per-serving variants. A product can legitimately say "high in fibre" while delivering 3 g in the portion you actually eat.

The fiber number is a total, not a description. Naturally-occurring fiber from whole grains and isolated added fiber from chicory root count identically on the panel. There is no line distinguishing them, so the ingredient list is the only place to find out which you're buying.

And serving sizes do work here too. A cereal claiming 5 g may be defining the serving as 45 g, which is considerably less than most people pour.

🔬 The five-second fiber triage:

1. Grams per realistic serving? Under 3 g and the claim is doing more work than the food.
2. What's the fiber source in the ingredient list? A whole food, or chicory root fibre / inulin / oligofructose / polydextrose?
3. Added sugars line. Frequently higher than the fiber.
4. Cost per 10 g? Divide. Over $1 and you're paying for the claim.

The honest exception

Two things on that shelf are genuinely worth buying, and it would be dishonest to lump them in.

Psyllium husk at $0.25 per 10 g is excellent value and has the best supplement evidence in the category (§11.9) — viscous, water-holding, minimally fermentable, and useful for LDL, glycemia, and both constipation and diarrhea. It sits near the top of the table for a reason.

Frozen vegetables at $0.70 are not the cheapest fiber, and they are cheap, they don't spoil during an overrun shift (Chapter 10, Case Study 1), and they solve a real logistics problem. Cost per gram isn't the only axis, and a chapter that insisted otherwise would be doing the thing it criticizes.

And raspberries at $3.50 are expensive and delicious and there is nothing wrong with buying them for that reason. The point of the table isn't that everyone should eat split peas — it's that if the goal is closing a fiber gap, the cheapest option is also the best-evidenced one, which is not true of any other nutrient in this book.

Analysis

1. The correlation runs backwards, again. Chapter 5's metabolism aisle, Chapter 8's protein aisle, Chapter 7's oat continuum, and now this. The pattern is consistent enough to be a rule: within a supermarket category, price and evidence are inversely related, because the plain version has no marketing budget and needs none.

2. Added inulin creates a specific harm beyond poor value. A person who buys fiber bars, gets uncomfortable gas from a concentrated dose of a single highly fermentable fiber, and concludes that fiber disagrees with them has been manufactured into §11.8's failure mode by a product. That's worse than wasted money.

3. The fiber number on a panel is genuinely uninformative on its own. It doesn't tell you the type (§11.2's four properties), the source, or whether it arrived with a food or in a truck. The ingredient list is doing the real work, which is true of most panels and especially true here.

4. Everything in this case study came from arithmetic and reading an ingredient list. No expertise, no study. Divide price by fiber; look at where the fiber came from; check the sugar. Ten seconds per product.

Discussion Questions

1. "High in fibre" is a regulated claim with a threshold most shoppers would find surprisingly low. Where should it sit? What would change if you doubled it, and who would object?

2. Should the Nutrition Facts panel distinguish intrinsic fiber from added isolated fiber? Some jurisdictions have moved partway toward this. What would it cost, and what would it clarify?

3. Inulin is genuinely fiber and genuinely prebiotic. Is a product that adds it to refined bread improving that bread, or laundering it? Does your answer change if the person eating it wasn't going to eat lentils anyway?

4. The chapter notes that frozen vegetables aren't cheapest but solve a logistics problem. Give two other cases in this book where the cheapest option isn't the right recommendation. What's the general principle?

5. Price and evidence are inversely related within supermarket categories, across four chapters now. Find a counterexample — a category where the expensive option genuinely has better evidence. What makes it different?

Your Turn

Go to a real shop with a calculator.

Find eight products: four making a fiber claim, four plain foods that don't. For each record:

Rank them by cost per 10 g. Then answer three questions:

1. How many of the claim-bearing products used chicory root fibre, inulin, oligofructose or polydextrose?
2. In how many did added sugar exceed fiber?
3. What would closing your fiber gap (from the Project Checkpoint) cost per year using the cheapest option versus the most expensive?

For most people that last number comes out somewhere between $50 and $2,000 for the same nutritional result — and finding out which end you've been shopping at takes twenty minutes.