How to Practise Gut Training Runs Properly

The gel that feels fine at 10 km can feel very different at 32 km. That is why you need to practise gut training runs, not simply carry nutrition and hope for the best on race day. Your muscles may be ready to work, but if your stomach cannot tolerate the carbohydrate, fluid and electrolytes required to sustain that work, your race plan is compromised.

Gut training is the deliberate process of teaching your digestive system to handle race-level fuelling under running stress. It is not about forcing down more than you can manage. It is about building tolerance progressively, testing the details and arriving on the start line with a protocol you trust.

Why gut training matters for endurance performance

At marathon pace, and particularly in the later stages of a long-course triathlon or ultramarathon, digestion is under pressure. Blood flow is prioritised towards working muscles and cooling. Impact, heat, nerves, concentrated drinks and an overly ambitious intake can all contribute to nausea, bloating, reflux or an urgent need for the loo.

The answer is not automatically to fuel less. Under-fuelling can mean fading pace, poor decision-making and a far harder final hour. For events lasting beyond around 90 minutes, carbohydrate taken during exercise helps preserve available energy and supports sustained output. The challenge is to match what your gut can absorb with what the event demands.

A trained gut can become more comfortable with regular carbohydrate intake during exercise. That does not make every athlete identical. Body size, pace, heat exposure, fluid losses, product format and individual history all matter. But a consistent process removes guesswork.

How to practise gut training runs

Treat fuelling practice as a planned part of training, just like intervals or long-run progression. A relaxed 45-minute easy run is rarely the best place to test a high-carbohydrate race strategy. Use long runs, race-pace blocks and selected brick sessions where the duration and intensity create a meaningful test.

Set a realistic carbohydrate target

Start with the demands of your target event. Many athletes racing for two to three hours can perform well with 30-60 g of carbohydrate per hour. For longer events, or where intensity remains high, experienced athletes may work towards 60-90 g per hour. Intakes above this range can be appropriate for some athletes, but they require a well-tested strategy and products designed around multiple transportable carbohydrates.

If you currently take very little, do not jump straight to an aggressive target. Begin at a level you can tolerate, perhaps 30-45 g per hour, then increase by 10-15 g per hour across successive long runs. Hold the new level long enough to assess it properly. One good session is encouraging, but repeated sessions tell you whether the plan is reliable.

Record what you took, when you took it, how much fluid you drank and how your gut felt. Also record the route, weather, effort and pre-run meal. A fuelling log turns vague impressions into useful decisions.

Rehearse timing, not just total intake

An athlete can consume the right total amount and still struggle because they leave it too late. Waiting until hunger, fatigue or a low patch appears often leads to taking a large dose quickly, when the gut is already stressed.

Start early and feed consistently. For many runners, taking a portion every 20-30 minutes is easier than taking a large amount once an hour. The right interval depends on the carbohydrate content of your gel, chew or drink, but the principle is fixed: small, repeatable actions are easier to execute under fatigue.

Practise opening packaging while moving. Practise taking fuel on climbs, at pace and when breathing is hard. If you plan to take a gel with water, do that in training too. Concentrated carbohydrate without enough fluid can be a common cause of discomfort for some athletes.

Match the session to race conditions

A cool, easy Sunday run does not fully validate a hot marathon strategy. Build race-relevant tests into your block. Include fuelling during sections at intended race pace, on tired legs and, where sensible, in warmer conditions.

This is particularly relevant when you expect to race in heat. Higher sweat losses change your hydration and sodium requirements, while heat itself can make the stomach more sensitive. Do not assume that a plan which works in winter will work unchanged in a warm race.

Use the same flavour, texture and delivery format you plan to use on the day. Flavour fatigue is real over several hours. A product that is pleasant for one serving may become difficult to tolerate after six. Consistency gives you better data, while occasional controlled testing helps identify a viable alternative before it becomes necessary.

Build hydration into the protocol

Carbohydrate, fluid and electrolytes work together, but they are not one fixed number for every runner. Sweat rate varies considerably between athletes and conditions. Drinking excessively can be as problematic as drinking too little, so use your thirst, the conditions and your own training observations rather than chasing a universal fluid target.

Sodium deserves the same deliberate approach. Athletes with high sweat losses, visible salt marks on kit or a history of cramping in hot conditions may need a more considered sodium plan. That does not mean assuming every difficult session is an electrolyte problem. Pace, conditioning, carbohydrate intake and heat management may be the limiting factor instead.

Choose products with clearly stated carbohydrate and electrolyte amounts so you can calculate your hourly intake accurately. A structured system, such as truefuels, can make this simpler because each serving has a defined role in the wider fuelling plan. Precision matters most when fatigue makes mental arithmetic unreliable.

Common mistakes when practising gut training runs

The most common error is treating fuelling as an emergency response. By the time you feel empty, it may be difficult to correct the deficit smoothly. The second is changing several variables at once: a new gel, stronger drink mix, larger breakfast and hotter route. If your stomach objects, you will not know what caused it.

Another mistake is making every long run a maximal gut test. Your digestive system responds better to progressive exposure than to repeated punishment. Use one or two purposeful fuelling sessions each week during a build, then keep easier runs genuinely easy when recovery is the priority.

Finally, do not ignore recurring symptoms. Mild fullness after increasing intake may settle as you adapt. Persistent sharp pain, vomiting, blood in stool, unexplained weight loss or symptoms that occur outside training deserve assessment from a qualified medical professional. Performance plans should never override health.

A practical four-week progression

For an athlete currently taking around 30 g per hour, a useful progression might begin with two long-run exposures at that level, using consistent 20-30 minute feeding intervals. In the following week, move towards 45 g per hour on a run of at least 90 minutes. Week three can test 60 g per hour during a long run with race-pace work. In week four, repeat the best-performing approach rather than automatically increasing again.

This is a framework, not a rule. If you are targeting a half marathon, your final target may sit below 60 g per hour. If you are preparing for an Ironman or ultra, your progression may continue over a longer period. The right endpoint is the highest intake that supports your race demands and remains comfortable, practical and repeatable.

Race day should be the least experimental day of the block. When you know what you can take, when you will take it and how it feels at pace, fuelling becomes one less decision to make. That certainty is valuable when the race gets hard.