Case Study 1 — Ten Weeks of Practice: Devi's Race Plan

Devi Raghunathan is an illustrative composite carried through this book — Chapter 14 (ferritin 11), Chapter 21 Case Study 2 (RED-S on 16:8), and here. ⚠️ The gut-training principle, the transporter physiology and the failure modes are real; the person is constructed.

Setup

Her energy availability was fixed. Her iron was fixed. Her total carbohydrate was fixed.

⚠️ She still had no idea how to eat during a marathon.

Her previous in-race fuelling, verbatim:

"A gel at halfway if I remembered. Water at the stations. I don't really like the gels, they make me feel sick."

That is roughly 25 g of carbohydrate across three and a half hours — ⚠️ against §23.5's recommendation of up to 90 g per hour for an event that long.

She was taking about 3% of what the physiology permits.

And the reason wasn't ignorance. It was that she'd tried more, twice, and been sick.

⚠️ The thing nobody tells you: the gut is trainable

This is the operative fact of the whole case study.

Tolerance for carbohydrate during exercise is not fixed. ⚠️ Intestinal transporter expression — SGLT1 in particular — is upregulated by repeated exposure to high carbohydrate intakes during exercise. Gastric emptying rate adapts too.

Which means "I can't tolerate gels" is usually a statement about your current training state, not about you.

And the corollary that ends most people's racing plans: ⚠️ attempting 90 g/hour for the first time on race day is the single most reliable way to produce vomiting at kilometre 25.

Devi had done exactly that, twice, and concluded she had a sensitive stomach.

The ten-week progression

One long run a week. Nothing else changed.

Ten weeks. 25 g total → 75 g per hour.

⚠️ Week 6 is the row that matters

She failed at 60 g/hour, and the reason was not the dose.

She had been using a glucose-based gel — glucose and maltodextrin, both of which arrive at SGLT1. ⚠️ At 60 g/hour she was saturating a single transporter, and the unabsorbed carbohydrate sat in her gut drawing water in. That is what the nausea was.

Week 7 changed the source, not the amount: ⚠️ a product using a glucose-to-fructose ratio, which recruits GLUT5 as well.

Same 60 g. No symptoms.

💡 Aha moment. ⚠️ She had spent two years believing she had a sensitive stomach. She had a transporter problem.

§23.5's mechanism, experienced from the inside: unabsorbed carbohydrate in the gut is osmotically active, draws water into the lumen, and produces exactly the bloating and nausea that athletes interpret as intolerance.

⚠️ The fix was not "take less." It was "take the same amount in a form that has two doors."

The other three things we changed

1. ⚠️ She practised at race intensity, not at easy pace. Gastric emptying slows as intensity rises. Fuelling that works on an easy long run can fail at marathon pace, which is why weeks 3, 6 and 9 were run at goal pace for their final third.

2. She rehearsed the mechanics. ⚠️ Where the gel goes, how to open it running, how much water it needs, which pocket. This sounds trivial and it is where race-day plans actually fail — a gel that needs two hands, or that can't be opened with cold fingers, doesn't get taken.

3. ⚠️ She used real food where she could. Two of the five hourly feeds became a small carbohydrate-dense snack rather than a gel, because ⚠️ palatability collapses after two hours and the fifth identical sweet gel is the one that gets skipped. This is the most underrated variable in ultra-endurance fuelling and it matters in a marathon too.

The plan, final version

⚠️ Total in-race carbohydrate: ~265 g ≈ 1,060 kcal.

Against a ~450 g glycogen store and a ~2,400 kcal race cost, that closes most of the gap.

And it is the difference between the arithmetic working and not working.

What happened

She ran the race. §23.15 has the outcome — kilometre 32 didn't arrive.

⚠️ What she said afterwards is the finding:

"I kept waiting for it. I got to 35 and thought — oh. That's just what it's supposed to feel like."

And then, later:

"Two years. I was doing the training the whole time."

Analysis

1. ⚠️ She was taking about 3% of the physiologically available carbohydrate, and had concluded the problem was her stomach.

2. The gut is trainable and almost nobody is told this. ⚠️ Ten weeks of graded exposure took her from 25 g total to 75 g/hour.

3. ⚠️ Week 6's failure was a transporter problem, not a dose problem. Single-transporter carbohydrate saturates SGLT1 around 60 g/h; the unabsorbed remainder is osmotically active and produces exactly the symptoms that get read as intolerance.

4. Practice at race intensity, not easy pace. ⚠️ Gastric emptying slows as intensity rises, so a plan validated at easy pace hasn't been validated.

5. ⚠️ Palatability is a real variable. Two of five feeds were deliberately not gels, because the fifth identical sweet thing is the one that gets skipped.

6. The mechanics were rehearsed. ⚠️ Plans fail on packaging as often as on physiology.

7. And nothing about her fitness changed. ⚠️ The final block added no training adaptation. It added fuel.

Discussion Questions

1. ⚠️ "I can't tolerate gels" is usually a statement about training state. How many other self-descriptions in nutrition are actually statements about a modifiable state? Name three from earlier chapters.

2. Week 6 failed and week 7 succeeded at the same dose. ⚠️ What would Devi have concluded if she'd stopped at week 6? How many athletes do exactly that?

3. The progression took ten weeks and one session a week. ⚠️ Why is this not standard practice? Whose job is it to tell a recreational marathoner about gut training?

4. ⚠️ Two of five feeds were deliberately not gels, for palatability. Is designing around psychology a compromise or good practice? Chapter 10 §10.4 has a view.

5. She ran the same fitness for two years. ⚠️ How would you estimate what fraction of endurance underperformance is nutritional? Design the study.

6. ⚠️ The "low fibre the day before" instruction struck her as strange. Explain why it's correct, using Chapter 11 — and say when that advice would be actively wrong.

Your Turn

⚠️ If you do any session over 90 minutes, build the progression. It takes ten weeks and costs almost nothing.

Step 1 — Establish your baseline.

Longest session: _ min · Carbohydrate currently taken: _ g/h · §23.5 says: ____ g/h

Step 2 — Build the ladder. ⚠️ One long session per week. Raise the target every 2–3 weeks, not every week.

Step 3 — ⚠️ If you fail, check the source before you lower the dose.

Is my product single-transporter (glucose/maltodextrin only) or mixed (glucose + fructose)? ____

⚠️ Above ~60 g/h, a single-transporter source will fail regardless of your gut. This is the single most useful diagnostic in the chapter.

Step 4 — Practise at race intensity, at least three times. ⚠️ A plan validated at easy pace is not validated.

Step 5 — Rehearse the mechanics. ⚠️ Opening it, carrying it, how much water it needs, cold fingers, one hand.

Step 6 — And plan for palatability.

After two hours, will I still want to eat this? _ What's my non-sweet option? _

⚠️ Write the whole plan down and take it with you. Devi's is six lines and she carried it in her kit bag for eleven weeks.