Weight Loss for Marathon Runners

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Running is a very accessible way to get fit, lose weight and provide an outlet for your competitive urges and, for a large proportion of runners, the marathon is the ultimate endurance challenge. Needless to say, if you want to run well, you need to conserve energy so that you don’t get too tired too soon. One way to do this is to avoid setting off too fast and practice good pacing but you also need to ensure you aren’t carrying any unnecessary weight.

Weight Loss Basics

Your body weight is made up from several components…

  1. Muscle
  2. Internal organs
  3. Skin
  4. Bone
  5. Water
  6. Minerals
  7. Fat

Of these seven, fat is the substance that makes running harder; for all intents and purposes, fat is “dead weight”. Some body fat is deemed essential but you really don’t need a lot of it to stay healthy. Ideally, your body fat level should be around 10 to 15-percent for men and around 15 to 20-percent for women.

A higher fat percentage than this will simply mean you are carrying more weight than you should and that means every mile you run will be more difficult than it needs to be. Fat is essentially stored energy and one pound of fat contains around 3,500 calories. For even the leanest athlete, this means that, in your body right now, you have at least 49,000 calories waiting to be used – sufficient energy to run around 490 miles! (Based on a 140lbs athlete with 10-percent body fat. 14lbs of body fat x 3,500 calories = 49,000 calories) While fat is stored energy, a little fat goes a very long way (one mile of running uses around 100 calories) so you don’t need a lot of body fat to fuel a marathon.

In fact, the leaner you are, the better your performance will be as the less dead weight you’ll be carrying. Imagine going for a run carrying a backpack weighing 10, 15 or even 20 lbs. Carrying that sort of weight is bound to slow you down and make you even more tired than you need to be. Now imagine doing the same run but without the added weight.

It’s obvious that you’ll be able to run further, faster and with more energy without that extra ballast holding you back. If you are overweight you are making your running training harder than it needs to be so it makes sense to try and drop some excess weight over the weeks and months that lead up to your marathon. Your running performance will improve not only because you are steadily getting fitter but also because you are getting lighter! Losing weight requires a calorific deficit. In other words you need to eat fewer calories than you burn on a daily basis. This energy deficit will then be met by your fat reserves. However, when you throw regular and demanding training into the mix, a typical low calorie diet can leave you feeling weak, tired and unable to train effectively. Not exactly what you need when you are preparing to run 26.2 miles! Most diets are not aimed at marathon runners but, instead, are designed for people who are predominately sedentary or who exercise relatively lightly. Losing weight (or more specifically fat) while training for a marathon requires a more measured, careful approach.

What is the Starvation Response?

The reason most low calorie diets and marathon training programs are incompatible is because of something called the starvation response… Turn back the calendar 10,000 years and imagine you are a Stone Age man. Stone Age man was very active but he wasn’t exercising for fun, health or recreation – he was constantly on the search for food and water which is why he is often referred to as a hunter-gatherer. When food was abundant, the hunter-gatherer lived well and his metabolic functions reflected this; he gained muscle, had lots of energy to spare, his metabolism was high and generally he was in good shape. However, from time to time, the hunter-gather was not so lucky and because of drought, lack of available game or an inability to catch or find anything substantial to eat, he experienced periods of starvation or, at least, a drastically reduced food intake. Thankfully for us, our ancestors were hardy types who had evolved to weather such problems but survival came at a cost. During times of starvation, hunter gather would have experienced the following…

  • Break down of muscle tissue for energy and to spare valuable fat stores
  • Reduced daily calorific expenditure due to lost muscle tissue
  • Increased propensity for fat storage
  • Increased fatigue due to lack of food
  • Increased hunger to motivate the hunter-gather to seek out new food sources

In a nut shell, during long periods of food restriction, the hunter gather lost muscle, needed fewer calories on a daily basis, made sure his fat stores lasted as long as possible and was primed for fat storage so that, when food become more abundant, he could store more fat to ensure he would survive any subsequent food shortages. Obviously, you are no longer a savannah-wandering hunter-gatherer but from a physiological point of view, you have not actually evolved very much and your body responds in a very similar way when you eat too little food or create a big calorific deficit by doing a lot of training. You body has no idea that you are eating less or exercising more voluntarily – as far as it’s concerned, you have failed to catch enough food to eat and it will take steps to ensure your survival! As a hard training marathon runner, the last thing you need is to lose muscle, feel more fatigued or increase your ability to store fat so, and for that reason, very strict diets are not advisable.

Related: 11 Things Runners Should Be Eating

How to Loose Weight and Maintain Energy

This creates a quandary – how do you lose fat while providing adequate energy to fuel your workouts and recovery? Get the equation wrong and you’ll lose weight but your running performance will suffer. Alternatively, you’ll have adequate fuel for your workouts but your weight will stay the same or may even increase. Like many things in life, the solution is a question of timing and balance. To force your body to burn fat for fuel while preserving or even building muscle, you must eat a little less but you must also eat smarter to encourage your body to use fat for fuel without triggering the starvation response. To do this, you are going to take advantage of several nutritional and physiological phenomena…

  • Cutting carb intake to promote fat burning
  • Timing carbohydrate intake around exercise
  • Increasing protein intake to boost metabolic rate
  • Consuming adequate “good” fats to normalize metabolism and hormonal profile
  • Reducing calorific and carbohydrate intake on rest days

Let’s discuss each of these strategies…

Cut Carbohydrate Intake

Low carbohydrate diets are very effective for fat loss. Carbs, found in foods like fruit, bread, rice, pasta, grains and potatoes as well as processed foods such as cereals, cookies and cakes, provide you with energy in the form of glucose. Glucose is the preferred source of energy for your muscles and your brain. Reducing your carb intake forces your body to preferentially use fat for fuel which is good news and helps explain why low carb diets are so popular. On the downside, cutting carbs below a certain threshold can leave you feeling tired and listless and unable to train with sufficient intensity and/or duration. Simply put, you need carbs in your diet if you are training for a marathon. However, many people, especially endurance athletes, consume far more carbs than they need to. Typically, carbs make up 60-percent of more of many people’s calorific intake which far more than is required unless you are training for an ultra-marathon or ironman triathlon. In reality, a diet containing closer to 40-percent carbs is more than adequate for the majority of runners and this decrease in carb intake will eliminate any competition for fuel so your body is much more likely to use stored fat for energy. You don’t need to resort to weighing or measuring your food to achieve a moderate reduction in carb intake – simply make a point to eat around a quarter to a third less bread, rice, pasta etc. Don’t worry though; you’ll be making up most of this calorific shortfall with extra protein and healthy fats so you won’t end up feeling hungry. Increase your intake of leafy green vegetables and watery vegetables so that you still have plenty of food to eat. You can often substitute vegetables for more substantial carbs; try shredding and lightly cooking cabbage and using it as an alternative to spaghetti or using layers thinly of zucchini in place of pasta in lasagna. Grated and lightly boiled cauliflower florets make an excellent low carb rice alternative.

Time Carbohydrate Intake around Activity

As mentioned, carbs are essential for fueling activity so it makes sense to maximize your intake around your training sessions and cut back when you are going to be more sedentary. This approach can best be thought of as earning your carbs. Carbohydrate, even the so-called slow-acting carbs like brown rice and oatmeal, are still digested relatively quickly. Once digested, carbs turn into glucose and are then transported around your body by your blood. From your blood, and in conjunction with the hormone insulin, glucose is shunted into your liver and muscles. If your body fails to use this carbohydrate-derived glucose, it is very likely to be converted into fat and stored or, at the very least, will interfere with fat burning by causing a competition for fuel. By timing your carb intake around exercise, you ensure the resulting glucose is used for fuel and is much less likely to be converted to fat. There are two main windows of opportunity for carb consumption – before and immediately after exercise… Pre-exercise carbs – by eating carbohydrates before exercise, you ensure your blood glucose levels are stabilized and that your muscle glycogen levels (glycogen being stored glucose) are optimized so you have plenty of ready-to-use fuel for your workout. Although running is primarily an aerobic activity which emphasizes fat for fuel, fat must be accompanied by adequate glucose. It is often said that fat is burnt in a glucose flame. If you consume insufficient pre-workout carbs or exercise exhaustively, you are likely to become glycogen depleted and that is essentially what “hitting the wall” is all about. Consuming good quality carbs before a workout will ensure you have enough glycogen for your run and that means the wall is a barrier you don’t have to concern yourself with. Make sure that you eat a good portion of carbohydrate-rich food exercise and, if you are doing an especially tough or long training session, you should supplement this with a carb-based sports drink consumed immediately before or during your workout. In terms of the timing your pre-training carbs, there are several factors to consider…

  • Type of carb consumed (high or low glycemic index – fast or slow acting)
  • Time of day – early morning training may make large pre-training meals problematic
  • Personal tolerance to food before exercise

These factors mean that your pre-training carbs could be consumed anywhere from 30 minutes to two hours before your workout. If you chose to eat high glycemic/fast acting carbs such as white bread or white rice, you can eat them closer to your workout as they are digested more quickly than slower acting/lower glycemic carbs such as brown rice. The more sugary the carb, the faster acting it is and the closer to your workout it should be consumed whereas the more fibrous the carb, the slower acting it tends to be. If, however, you are an early morning runner, getting up two hours before your intended run time may well be far from ideal so consuming a fast acting carb-based sports drink may be preferably. Finally, some people need longer for gastric emptying to occur – gastric emptying being the length of time it takes food to leave your stomach and enter your gastrointestinal tract. Running with stomach heavily laden with food can be very uncomfortable so adjust the timing your pre-run carb intake to suit the speed at which you digest food. Post-exercise carbs – once your workout is finished, your glycogen stores will be depleted. The extent of the depletion depends on how far and fast you ran and how well-stocked your glycogen stores were when you started. In all scenarios, to ensure you rapidly and effectively replenish your glycogen stores, your muscle and liver cells are very sensitive to the action of the hormone insulin. Insulin acts like a key to your cells so that carbohydrates consumed in the two or so hours after exercise are preferentially taken up into your liver and muscles to replace lost glycogen. The more sensitive your cells are to insulin, the more carbohydrate will be shunted into your liver and muscle cells for later use. Carbohydrate consumed at this time will not be converted to fat and nor will it interfere with fat burning. Insulin sensitivity starts to decline and return to normal once two hours or so have expired so it is essential that you consume a carb-rich meal (or even two) as soon after exercise as you can. This will promote a speedy workout recovery so that, when you next run, your glycogen stores are topped up nicely. In summary, the majority of your daily carbohydrate intake should be split between the pre and post-exercise periods. Pre-exercise carbs provide fuel for your workout and should be consumed 30 minutes to two hours before your workout depending on the type of carbs consumed, the time of day and your personal food before exercise tolerance levels. Post-exercise carbs replace what you have used so you are refueled and able to exercise again tomorrow and should be consumed as soon as possible after you finish your workout and for up to around two hours thereafter.

Increase Protein Intake

While protein is not really a viable source of energy for runners, it can be very helpful in your quest for weight loss. Many endurance athletes place an large emphasis on carbohydrate but all but neglect protein which is commonly associated with weightlifters and bodybuilders rather than endurance athletes. Contrary to popular belief, protein is very important for endurance athletes and weight loss too…

  • Protein has a muscle-sparing effect which is important when you are trying to lose fat and maintain a healthy metabolic rate. Muscle loss results in a reduced metabolism, a lowered daily energy expenditure and therefore slower fat loss.
  • Protein has a high thermal effect – this simply means that eating protein-rich foods such as chicken, beef, eggs and fish will elevate your metabolism more than carbohydrates and fat. Protein takes a lot of energy to ingest, digest, absorb and utilize; think of eating protein as a calorie burning workout for your digestive system!
  • Protein foods help keep you feeling fuller, longer – as you’ll be reducing your carb intake by roughly 20-percent, you could end up feeling hungry and nothing derails good nutritional practices faster than hunger gnawing at your belly! Replacing some of your lost carbs with protein means you’ll feel just as full as usual and will avoid the hunger trap.

Make sure you include a good portion of protein in every meal you eat – with the exception of your pre-exercise meal where the emphasis should be on carbohydrates. If you are not a meat eater, this means dairy, nuts, legumes etc. There is no need to measure your portions – just make sure that your protein food is approximately the volume or size and thickness of a standard deck of cards. Consume Adequate “Good” Fats  Many dieters reduce fat intake to lose weight. This makes a certain amount of sense because, of all the food groups, fat provides the highest number of calories. Where protein and carbohydrate have four calories per gram, fat weighs in with a whopping nine calories per gram. Subsequently, a low fat diet is usually a low calorie diet. However, cutting fat intake too low can have an adverse affect on your hormonal balance. Fat consumption is directly linked to the formation of anabolic hormones – specifically testosterone and growth hormone but also insulin. These hormones are responsible for building/maintaining muscle, promoting post-exercise recovery and burning fat. Low fat diets can reduce anabolic hormone production and that is bad news indeed. Low fat diets may also make your body hold onto your fat stores more tightly than normal. If you drink less water, your body will reduce urine output to prevent dehydration. Drink a lot of water and you’ll pee like a race horse! Likewise, if you eat adequate amounts of dietary fats, your body is more inclined to burn body fat. Cut fat levels too low and suddenly your body fat becomes a very valuable commodity which will be jealously stored rather than freely burnt. Some fats are definitely better for you than others and while it makes sense to limit (but not eliminate) the consumption of saturated fat, mono and polyunsaturated fats should be consumed fairly abundantly although steer clear of trans fats as they are very unhealthy. Between 20 to 30-percent of your daily nutritional intake should come from fat – split evenly between saturated, mono and polyunsaturated. As protein and fat are normally packaged together in meat, eggs and dairy etc, make sure you consume fish, seeds and nuts on a regular basis to get adequate unsaturated fats in your diet. It’s also worth remembering that low fat foods such as fat-free ice cream or reduced fat cookies are usually very high in sugar and not as healthy as they might otherwise seem to be. Don’t fall into the “low fat trap” – eat sensible amounts of natural fats for health and performance.

Reduce Calorific and Carbohydrate Intake on Rest Days

Running a mile burns approximately 100 calories so it makes a lot of sense to eat a little more on your training days to fuel your workouts. Cutting calories too aggressively on training days can leave you feeling flat and unable to train as hard as you want. However, if you are having a rest day (and you should be resting two to three days a week so you can recover adequately from your workouts) it makes sense to eat less on the days you do not run. Ideally, on non-training days, you should eat around 500 calories less than normal to allow for the fact you are not going to be as active. You can do this in several ways…

  • Skip one meal entirely – you won’t be consuming a pre or post-training meal so this is easy to do
  • Reduce the size of each meal you eat
  • Eliminate any and all high calorie treats on training days
  • A combination of the above

However you do it, eating less on training days just makes sense as unused calories will be converted to fat and while you might not gain weight, weight loss will probably stall. If you are relatively active on your rest days, i.e. you do a light recovery run or pre-hab/re-hab work in the gym, still reduce your food intake for the day but do not be so aggressive. A 200 to 300 calorie reduction should be sufficient to ensure some weight loss but no loss of performance. Ensure you still consume an adequate post-training carb-based meal to facilitate recovery.


Losing weight, specifically fat, should enhance your running but only if you do so without triggering the dreaded starvation response and while ensuring you eat sufficient amounts of food to fuel your grueling marathon training regime. Drastic diets can certainly help you lose weight quickly but, often, this weight ends up being muscle and that will leave you feeling tired and unable to train properly. Most diets are not designed for hard training marathon runners. Instead, make less dramatic changes to your diet to ensure your weight loss is slow and relatively painless. Don’t try and lose weight too fast but, instead, aim for around one pound per week. While faster weight loss is possible, you are more likely to trigger the starvation response and remember these rules for simple fat loss while training for your next marathon…

  • Reduce carb intake to approximately 40-percent
  • Consume the majority of your carbs before and after exercise
  • Increase your protein intake
  • Consume plenty of healthy fats
  • Eat a little less on rest days

This article was written for RunnersGoal.com by Patrick D., a guest author.  Patrick is a personal trainer with expertise in nutrition and weight loss.   

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