Training your gut to absorb 90g of carbs an hour

Can you really take on 90g of carbs an hour? Yes, but almost nobody can do it off the couch. The gut is trainable like any other system, and the athletes hitting those numbers in races got there by practising for weeks in training, not by panic-buying gels the night before.

Here is the honest version. Most age-groupers massively under-fuel, then blame the product when their stomach turns. The carbs were never the problem. The bottleneck is absorption, and you fix that with deliberate, progressive practice.

Why there is a ceiling at all

Your small intestine moves glucose across the gut wall using a transporter called SGLT1. On its own, that transporter saturates at roughly 60g of carbohydrate an hour. Pour in more glucose and the extra just sits in your gut, drawing water in and giving you the bloating, cramping and worse that ruins long efforts.

The trick, established largely by Asker Jeukendrup's lab, is to use a second sugar. Fructose crosses the gut wall via a different transporter, GLUT5. Because the two pathways do not compete, combining glucose and fructose lets you absorb more total carbohydrate at the same time. A glucose:fructose mix can push exogenous carb oxidation to around 90g an hour, roughly a 50% jump over glucose alone, and in one well-known 100km time-trial study that translated to about an 8% performance improvement.

The ratio that matters

Older products used a 2:1 glucose:fructose blend. Newer research suggests something closer to 1:0.8 glucose:fructose lets you go higher still, into the 90g and beyond range, because fructose absorption is the limiting step at the top end. For most people the practical takeaway is simple: any modern dual-source product, and most homemade mixes, will get you there. Don't agonise over decimal points on the ratio. Get the total dose up first.

How long it actually takes

Gut training is not a one-session fix. Plan for weeks.

WeekTarget carbs/hrWhat you're doing1-240-50gBaseline. Practise eating on every long session.3-460gAdd a second source if you haven't.5-675gThis is where most people feel the first wobble.7-890gRace pace, race products, race timing.

Add roughly 10-15g per hour every two to three weeks. The exact pace depends on you. Some athletes tolerate big jumps; others need to creep. The principle is overload then adapt, the same as training your legs.

How to practise without wrecking sessions

A few rules that save a lot of grief:

• Train the gut on the sessions that look like your race. A marathoner practises at marathon pace on long runs. A triathlete practises on the bike where the eating actually happens. Don't only ever test fuelling on easy spins.

• Drink to the dose. High carb concentrations need enough water to clear, or they sit and ferment. If you're running gels, take water with them.

• Eat early and keep it steady. Don't wait until you feel empty. A small, regular drip is far easier on the gut than panic-feeding when you're already bonking.

• Keep a simple log of what you took and how it sat. Patterns show up fast.

Running tolerates less than cycling

A key honesty point: the gut handles fuel better on the bike than on the run. The mechanical pounding and the more upright, jostled gut of running make high doses harder. Many strong runners cap out around 60-75g an hour where a cyclist of the same fitness happily takes 90g. Swimmers and triathletes fuel mostly on the bike leg for exactly this reason. Don't assume a number that works on the turbo will work on your feet.

When 90g is overkill

You do not need 90g an hour for a 90-minute effort. Below about two hours, 30-60g an hour covers most people. The big numbers earn their keep in long road races, Ironman, ultras and marathons, where total fuel over many hours is what keeps you off the rocks. Match the dose to the duration, not to what the fastest rider in your club posts on Strava.

What it costs

Gut training itself is free. The carbs you practise with are the only cost, and you can keep that down with a homemade glucose:fructose drink mix for a fraction of branded prices. The expensive mistake is skipping the practice, blowing up on race day, and writing off a season's training over a fuelling problem you could have solved for the price of a bag of maltodextrin.

FAQ

How do I know if I'm absorbing it or just stuffing it in? If you can hold the dose for the full session without bloating, nausea or urgent toilet stops, and your energy holds, your gut is keeping up. Persistent GI distress means back off and build slower.

Can I lose the adaptation? Some of it, yes. Like any training response it fades if you stop. Keep practising through the weeks before a key event.

Do I need fructose, or can I just take more glucose? You need the second source to get meaningfully past about 60g an hour. Glucose alone hits a hard ceiling no amount of gut training moves.

In MOVE we set your hourly carb target by session length and sport, so the numbers you practise with are the numbers you'll actually need on the day. Build the gut to meet them, and fuelling stops being the thing that decides your race.