For endurance and ultra runners

You have already run the experiment. Nobody wrote down the result.

Every long run was a test of what your gut takes, in heat and climb and hours you will meet again on a start line. Absorb is the record you never kept, and the race plan that comes out of it.

Join the waitlist See how it works

Not open yet, as of August 2026. Two emails at most.

Same gel. Different day. Different gut.

Four studies. Four things that were not the carbohydrate.

The hour

The same three hour run at 9pm emptied slower than at 9am.

Randomised crossover in runners. More gut symptoms, and a much larger cortisol rise.
PubMed 33065594
Three days before

The runners worst hit had eaten more polyols in the days beforehand.

Field study at a 56km trail ultramarathon. Total FODMAP intake showed nothing.
PubMed 38637153
The heat

Yesterday’s dinner changed symptoms during today’s run.

Randomised double-blind crossover, 18 endurance runners, two hours at 35 degrees.
PubMed 31652404
Your head

How anxious you were on the start line tracked with how your gut went.

Prospective field study at a 56km ultramarathon, strongest in the final 24 hours.
PubMed 34897557

Running has a prescription problem. Take 60 to 90 grams an hour, as though the gel were the only variable in the room.

Absorb is the other way round. Your runs are the evidence, published guidance is a starting point, and the answer is allowed to be yours rather than the average.

The day it goes wrong, you rarely find out why

Hour eleven, a climb you have never done on tired legs, and a stomach that stops taking anything. You walk it in, or you stop. Months later you cannot remember what you had been taking, how warm it actually was, or whether the last three long runs had already been telling you something.

Injury ends some races. Fuelling and the gut end a lot of the rest, and unlike the weather it is the part you can rehearse. The problem is that rehearsing it only counts if somebody wrote down what happened.

Absorb cannot tell you why that day went wrong. It can tell you which of those conditions you had runs behind, and which you did not.

What Absorb is

Absorb is a fuelling memory and race-planning tool for endurance and ultra runners. It records what you took on during each run and how the run went, keeps the conditions that run happened in, and turns the accumulated memory into a course-specific plan, a console for your crew, and afterwards a piece of evidence that sharpens the next one.

It is not a nutrition app, a macro tracker, a training plan or a coach. It does not tell you what to eat, does not count calories, and does not claim to know why anything happened. It is built by an ultra runner in the UK, and it works from your own training history.

The evidence gap

If you are a woman, the research was not written about you

We went through the research. Not one study tracked cycles closely enough to say what works for you. On hormonal contraception, which more than half of female endurance athletes use, there is nothing at all: researchers usually leave contraception users out of the sample.

We did not set out to build a cycle feature. We went looking for the evidence, found how little of it was about women, and built you somewhere to gather your own.

See the research we cite

Studies on fuelling during exercise: 937 over 11,000 athletes
Of those athletes, about: 1 in 10 were women

Absorb never predicts a phase and never adjusts your fuelling by one. It records what you tell it, in your words, and shows you what your own runs say.

Before you log anything

On day one it will tell you about a race you ran three years ago

Connect Strava and Absorb rewinds to the morning of each race you have already finished, using only what you had logged before that start line. Then it shows you the range it would have given you, and where you actually landed.

No waiting to accumulate data. You already have the data. This is the part that tells you whether any of the rest is worth trusting, and it is free.

See how we check ourselves

Inside the range: The evidence you had held on the day.
Faster than your data supported: Either you found something on the day, or it was missing evidence.
Could not be called: Listed with the reason, never quietly dropped.

Hits and misses both. A range that only ever reports its wins is not a check on anything.

Four things it does

The first is free and you will use it every week. The next two are what you pay for. The last is why you should believe any of it.

How it works

Connect Strava, mark the point a run turned, and watch your own pattern appear. Then run a real test on yourself, backed by a citation.

Race day

Paste the race URL and get a stop list. A finish range rather than a finish time, fuelling planned per aid station, and reminders written into your GPX.

Crew

Your crew get the same plan on their own phones. No account, nothing to install, and it still reads with no signal.

Proof

We publish the races the engine missed, not only the ones it called. And why Absorb refuses to hand you a prescription.

The memory is free. The race is paid.

Logging, every insight, your racing record and the day-one check above cost nothing, and it is not a trial.

See what is free and what is paid

Founding, first 100: £100a year, forever
After that: £199a year

A founding place renews at £100, not at the list price. That is £99 a year less, every year, not just the first.

Common questions about Absorb

Which watch do I need?

Absorb works with Strava, and Strava is the only connection it needs. Garmin, COROS, Suunto, Polar and Apple Watch all sync to Strava automatically, so if your runs already appear there, Absorb can read them.

Direct connections to the watch brands are not live yet. Everything Absorb needs is already in what Strava has.

Do I have to log every run?

Absorb only asks about runs long enough for fuelling to matter. You set that length yourself when you sign up, and anything shorter is skipped without being counted against you.

If you want to log a short run anyway, you can open it and do so. A run that went fine takes two taps.

How long before Absorb tells me anything useful?

Absorb says something on your first logged run, and something worth acting on after about five. The first run gives you where it sat among your conditions. From two runs in the same condition it will name what has coincided, and it says so in careful language, because two runs is two runs.

Below two runs it says nothing at all rather than guessing.

What does Absorb cost?

Absorb keeps the part you use every week free, and it is not a trial. Logging runs, everything in insights, your race results and retrodiction cost nothing. Planning a race is the paid part: the course, the pacing, the per-stop fuelling and the crew console.

The first 100 members pay £100 a year and keep that price for as long as they stay. After that it is £199 a year, or £20.99 a month. See the full breakdown.

Is Absorb a nutrition tracker, or a coach?

Absorb is neither. It is a memory and calibration system, not a nutrition app, a macro tracker, an optimiser or a training plan. It does not count calories, does not build you a meal plan, does not tell you what to eat and does not write your week. It remembers what you did and what went with it.

It is meant to sit alongside a coach, or alongside your own judgement, as a cross-check rather than an authority.

Be there when it opens

Absorb is not open yet. Leave your email and we will tell you on the day it is.

For people aged 16 or over. We store your address and the date you agreed, and nothing else.