How To Avoid Marathon Weight Gain

Why you may put on weight while training for a marathon and how to stop it from happening

How To Avoid Marathon Weight Gain

Many women take up running to lose weight and, for most of us, it works in the beginning. Running is one of the best ways to boost weight loss – it can burn anywhere from 10 to 15 calories per minute, depending on your age, weight, fitness level and how fast and how long you run. As a new runner, you’re creating a different stimulus to which your body must adapt, so the body finds it challenging at first, resulting in more energy expenditure. However, once your body gets used to it, weight loss can plateau, especially if you stick to the same type of runs. Simply clocking up more miles is not necessarily the best way to lose weight and if you think that doing a marathon is an invitation to eat what you want, then you may be in for a shock!


Many female runners I’ve spoken to have been shocked to gain weight while marathon training. “I gained weight during my first marathon,” says 28-year-old running blogger Charlie Watson ( “Mostly because I would get back from an 18-mile run and think I could eat whatever I wanted. I gained about half a stone and I was outraged! I couldn’t believe I’d run a marathon and not only had I not lost weight but I had put it on. I felt conned!” Julia Buckley, PT and author of The Fat Burn Revolution, (, ran marathons and ultras and still struggled to lose weight. “At first the fat comes off, but then it stops shifting. So you push yourself by exercising for longer. With the increase in training a bit more fat comes off, but then fat loss stalls again. Your body keeps adapting to cope with the longer sessions.” Julia switched to shorter, high-intensity interval training sessions to lose weight and it worked.


“Understanding how your body functions will help you to eat correctly,” adds PT and ultra runner Anne-Marie Lategan, author of the running nutrition programme, Eat Better Run Faster ( “Most of us have enough energy (glycogen) stored in our muscles and liver to run for at least 60-90 minutes. So you don’t need to overeat on calories before your run. You should eat enough for your body weight before you run and then top up with fast-releasing calories (an energy gel or sports drink) during your run – but only if you run for more than 60-90 minutes.”

On a basic level, it is assumed that 1kg of bodyweight uses around 25 calories of energy per day. So to calculate your daily calorie requirements, multiply your weight in kilograms by 25 to get your resting metabolic rate, and then add on the following depending on your activity levels:

Sedentary person – add on 20% of your RMR
Moderately active person – add on 50% of your RMR
Very active person – add on 100% of your RMR

It’s important to look at your overall lifestyle. If you have a sedentary job and you only run three times a week, then you’d most likely be classed as moderately active, or at best, somewhere in between moderately and very active. So if you weigh 60kg and you are moderately active, your daily calorie requirements could be calculated as follows:

25 x 60 = 1500 calories per day
Then add on 50% of RMR = 2,250 calories required daily

Another method for tracking calories burned during each run is to use a sports watch. Although this will vary depending on the type of training session and the duration of each run, you’ll get an idea of total calories burned during a typical week and that will tell you how many extra calories you will require. If you burn an extra 2,000 calories per week by running, you’ll only need an extra 285 calories per day. On rest days, it may be worth trying to reduce your calorie intake. If this results in you feeling more tired, up your calorie intake slightly on these days.

How To Avoid Marathon Weight Gain

One kilogram of bodyweight uses around 25 calories per day


The timing of when to increase food intake is key. “The trick is to up your energy intake around your training,” says James Rutherford, an ambassador for nutrition brand Bio-Synergy, who has a BSc (Hons) in Sport and Exercise Science ( “Your pre-training and post-training meals should be the largest of the day, as these are the meals that are fuelling and refuelling your body for exercise.”


Cravings can cause problems for many marathon runners. “Feeling hungry and having cravings are probably the two biggest problems runners face when increasing their distance,” says Anne-Marie Lategan. “Reducing cravings is most easily done by increasing leptin levels – the hormone released by fat cells that signals satiety,” says Rutherford. “This can be done by focusing on sufficient protein intake from lean meats, fibre intake from grains, fruit and vegetables and omega-3 intake from fresh fish such as salmon.”


So how much extra should you eat the night before your longest runs? “There is no need to hugely increase calories the night before so long as the daily calorie intake is adequate to meet daily energy expenditure,” says Rutherford. “Focus on prioritising complex, low-GI carbohydrates the night before a big run as this is the meal in which the majority of your energy will come from, especially if the run is early the next morning.”


Make sure you consume enough carbohydrates to fuel your runs, as carbohydrate is the body’s preferred source of energy. Aim for around 60-70% of your daily calorie intake to come from carbohydrate sources, around 20% from fat and around 15-20% from protein. When it comes to sensible carbohydrate choices, aim for fruit, vegetables, pasta, rice and potatoes. Choose healthy fats like avocado, oily fish and nuts. Fat is the body’s second preferred energy source and is typically converted into fuel when carbohydrate stores have been depleted (after around 90 minutes).

How To Avoid Marathon Weight Gain

Aim for around 20% of your daily calorie intake to come fats


Keep an eye on your food portions. Many foods contain more calories than we think. Weighing out foods is a good way to control portion sizes and ensure you’re getting enough of the right macronutrients in every meal.


But keep in mind that marathon training isn’t the time for strict dieting. “Immune function is essential for marathon training as the body takes a battering from all the stress involved and the immune system is weakened,” says Rutherford. “This increases susceptibility of illness and injury. Ensuring sufficient mineral and vitamin intake through eating lots of fruit and vegetables will help to combat this.”

Chris Macdonald

Written by Chris Macdonald | 348 articles | View profile

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