Committing to training for a marathon can result in a slew of changes to your lifestyle, the most notable of which being that you’re going to start running a whole lot more (if that comes as a surprise, maybe this whole marathon thing is a bad idea).

Your diet is also going to change during marathon training. That doesn’t mean you’ll be shovelling down huge bowls of pasta every day – although there will certainly be times when you will be, it’s one of the perks of running a marathon – but you will need to start eating more of certain foods on certain days, and you’ll probably start experimenting with supplements to fuel your long runs in particular.

For all the advice you need on what to eat while training for a marathon, we spoke to expert in the field Tim Lawson, director and founder of sports nutrition brand Secret Training.

What are the main general changes to a diet someone training for a marathon should make?

There is some dietary advice that never changes, regardless of the situation.

“The general advice is no different than what is recommended for a regular healthy diet,” says Lawson. “Less alcohol, lots of greens, oily fish and quality protein foods evenly spaced through the day, with sufficient fluids.”

Carbs are also key, but don’t go overboard.

“Carbohydrate-rich food like pasta, rice and oats should be regarded as fuel for training sessions,” says Lawson.

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“A mistake amateur athletes often make is to eat the same high-carbohydrate breakfast day in, day out, whether they are fuelling for a gruelling training session or sitting in the office all day.

“Carbs that are not used as fuel for training are quickly stored as fat. So if you are not training, think more along the lines of a boiled egg than a huge pot of porridge. Just because you are a marathon runner it doesn’t mean that every meal needs to be loaded with pasta.”

Right now you might be angry – perhaps you were wooed by the promise of endless carbs when you signed up for a marathon. One positive way to look at not going overboard on carbs, or junk food in general, is that it’s an easier way to get better at running than logging more miles.

“The biggest performance gains may be from increasing power to weight ratio by losing mass rather than doing more mileage,” says Lawson.

“Reducing the consumption of any junk calories is an obvious start point. For example, every 13 pints of beer you don’t drink (that you normally would do) in the run-up to a marathon is likely to result a reduction in race weight of 1kg. This will have a significant effect on performance.”

Should you increase your calorie intake in line with your mileage throughout a training plan?

Building on the above, Lawson recommends looking at your overall weight when determining your calorie intake, as well as the training you are doing.

“Increasing your calories in line with training is something you only need to do if you are at your optimal race weight,” says Lawson.

“In practice people seldom are, and even top elite athletes will try to reduce their body fat for specific events. When training sessions become harder and longer they will need fuelling appropriately, but away from training the biggest gains may be had from portion control.”

So unless you’re already at your ideal weight, adding extra calories to your diet during training might be counterproductive. Of course, there are limits to this.

“If weight loss become severe or your training sessions start to suffer, then your calorie intake needs to increase,” says Lawson.

How quickly after training sessions do you need to eat?

“There are some studies that show that enzyme activity is most active within 20 minutes of finishing exercise and this has led to an emphasis on refuelling within that 20-minute window to maximise recovery,” says Lawson.

“Other studies show that with adequate carbohydrate provision it is possible to replace carbohydrate stores within 24 hours if this window is missed.”

When deciding when and what to eat after a run, it’s important to consider not only the training you’ve just done but also what you plan to do next.

“If your next session is a recovery run there is less necessity to consume carbohydrates quickly than if you’re doing back-to-back intervals sessions with a short recovery period,” says Lawson.

And it’s not just carbs you need to consider.

“You should also consume protein as soon as possible after exercise to aid recovery,” says Lawson. “And it is also important to remember to rehydrate and replace sodium and potassium. Many runners use an electrolyte drink for this.”

How should people use supplements to help their training?

Even if you have never used supplements to support your workouts before, the demands of marathon training can make them invaluable, if only for their convenience.

“Supplements have their uses. For example, it is far easier to consume a protein gel containing cherry anthocyanin antioxidants just after a training session than a can of tuna and 40 cherries,” says Lawson.

Different supplements have different uses, usually related to when you take them.

“Before exercise a carbohydrate drink or gel or even a caffeine energy gel may help to provide the energy to complete a session if life has got in the way of optimal preparation,” says Lawson.

“During your sessions, carbohydrate gels and drinks can be the best way to maintain energy levels. Using them during some training sessions serves as practice for the event, and may improve the quality of those sessions.”

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“After training protein-based recovery drinks and gels provide a convenient way of refuelling.”

It’s vital to plan what you are going to eat and drink, especially with regard to post-workout refuelling, as the right supplements can help you recover faster.

“Don’t leave it to what’s available in the vending machine or in the fridge at home,” says Lawson.

“There is increasing evidence that anthocyanin-based phytonutrients from berries, cherries and the like can reduce inflammation and improve recovery. Similar effects have also been observed with turmeric and its extract curcumin.”

Tim Lawson has a BSc (Hons) in Sport Science and an MSc in Sport and Exercise Physiology, and over 30 years’ experience of working in sports nutrition