Eating The Burn: WHAT to Eat ? Carbs


This is the third episode in my Eating The Burn Serie in which I’m attempting to investigate what, how much and when I should be eating as I train for the upcoming Paris marathon.

In Part One, I ran a detailed look at what I currently consume on a typical marathon training day compared with what I “should” be eating/drinking according to some of the many running books, magazines, articles, internet and other sources of information out there. In Part Two, I ran through what I ate and drank on my long run (20 mile) day, and again compared this to what I estimated I should be consuming on such a heavy training day. In this episode, I want to look at the types of food and drink that I typically eat and drink while training for a marathon Vs. what I’m allegedly “supposed to” be consuming.

We’ve already established that how much you need to consume each day is variable for every individual and depends on factors such as your height, weight, sex and daily training. Now we want to look at how those calories should be divided up on an average day – As a runner, what is the best way to get your energy requirements?

Carbohydrates: NO WAIT! Don’t leave 🙂 !! I’m right there with you -I don’t know how many articles I’ve clicked on in the past claiming to be able to tell me more about what I should be eating as a runner and/or during training for a marathon, for said article only to turn around and tell me that… wait, what?! Eat more carbs. NO! Really? Groundbreaking.


Do runners need to be consuming carbohydrates when training? Quick answer: yes.

Quick science? Carbohydrate provides the most readily available source of fuel for muscles to use in moderate to high intensity exercise. Carbs are broken down by the digestive system, carried around the body as blood glucose and this glucose is stored in muscle and the liver as glycogen to be used by the body during activity. Your muscles use the stored glycogen as their primary energy source with blood glucose as an additional source. When muscle glycogen becomes low, fatigue occurs in the muscles being used. Muscle glycogen depletion occurs after 2-3 hours of continuous training at low intensity. (Okay, so that wasn’t so quick but stay with me 🙂 )

Now, I don’t think I was that bad at math in school but seems to me that there are a lot of different calculators, equations and percentages being quoted as regards how much carbohydrate a runner should be eating day in, day out. I am somewhat confusseded.


How much?

Nancy Clark’s Food Guide for Marathoners (2011) – Says that between 55-65 % of your daily calories should come from carbohydrates. She also says that carbs should make up the foundation of every meal, every day (p106). When carbo-loading, she recommends consuming between 3-5g of carbs per pound of bodyweight.

Douglas and Pfitzinger – Advanced Marathoning (2009). These guys say that you calculate your carbohydrate requirements based on your weight and how much you’re training. They say that if you are averaging between 1-1 1/2 hours of training per day, you need approximately 3-3.5g of carbs per pound of bodyweight per day. If training for over 2 hours, you need 4-4.5g per pound of bodyweight per day.

International Olympics Committee Report on Nutrition For Athletes (2012) 
– The IOC note that an athlete’s carbohydrate needs are closely tied to the muscle fuel costs of their training and that because training load changes from day to day, and from training period to training period, an athlete’s intake of carbs should rise and fall in accordance with their muscle fuel needs, rather than remain static or fixed.

In relation to daily targets, the IOC suggest that while general targets are fine, these should be fine-tuned according to an individual’s energy budget and feedback from how well they are training. They suggest that carb intake might be increased on days involving hard training, high intensity or with high quality to ensure that they have adequate muscle carbohydrate stores to fuel these goals. In other words, when training needs increase, so does carbohydrate intake. It’s not going to be the same everyday.

Like D & F and Nancy, IOC recommend that carbohydrate targets should be provided in terms of grams relative to the athlete’s size (Body mass) rather than as a percentage of total energy intake. They even did a helpful little chart:

Training Level Carbohydrate Intake Targets

(g per kg of athlete’s body mass)

Light/ Low Intensity 3 – 5g /kg
Moderate Intensity (1 hour per day) 5 – 7g/ kg
High Endurance Program (1-3 hours of mod-high intensity exercise) 6 – 10 g/kg
Very High / Extreme Commitment (4-5 hours per day of mod – high intensity exercise) 8 -12 g/ kg

The IOC report is well worth reading and just to highlight some of what they say in relation to carbohydrates, in particular (because let’s face it, they know lots more about this than I do!):

Rather than talk about “high carbohydrate diets” and “low carbohydrate diets”, we should now consider carbohydrate availability relative to the muscle’s fuel needs – is the total intake and timing of the day’s intake able to meet the fuel demands of a workout (= high carbohydrate availability), or are carbohydrate stores depleted or sub-optimal in comparison to the muscle fuel demand (= low carbohydrate availability).

The table above shows that very different amounts of carbohydrate may be adequate for different training loads. Therefore two athletes could eat the same about of carbohydrate, but according to their training needs, one could achieve high carbohydrate availability whereas the carbohydrate availability of the other athlete is low.

Many athletes do some of their training sessions with low carbohydrate availability – for example, when they train first thing in the morning without breakfast, when they go for a long workout without access to food or a sports drink, or when they reduce their energy intake to reduce body fat levels. This may not be a problem during the base phase of training or on days of light training, when training intensity and quality is low. In fact, some studies suggest that doing some training sessions in this way provides a good stimulus to the muscle to help it adapt to training. Of course, such strategies need to be periodised into the training program so that they don’t interfere with training intensity

When athletes train more than once per day and sessions are close together, speedy recovery of the muscle carbohydrate stores is essential. Consuming carbohydrate-rich foods and drinks soon after the session helps with rapid refuelling, since the muscle can’t store glycogen effectively in the absence of carbohydrate intake.”

The IOC go on to discuss the timing of carbohydrate intake in more detail which you can read about by following the above link or I’m also planning to discuss timing as a topic of running nutrition in a follow-up post, if you can wait that long 😉

Conclusion on Carbohydrates: The amount of carbohydrate a runner needs to consume on a daily basis depends firstly on your own characteristics: sex, age, height and weight; and secondly, it depends on the training you do on any one day. Maths, people. It keeps coming back to the maths.

The only quibble I have with any of this is that there is something of a variation between the recommended calculations (ie. Nancy Clark, D & F, the IOC, etc). Yes, there are similarities but what I’m getting from all of it is that there are no exact figures because it is not an exact science. At least not yet anyways. For example, they all give approximate, or rough, figures like 3-5 g per kg of body mass  for “low intensity”, which (a) there is quite a difference between 3 and 5 g per kg of body mass and (b) terms like “low intensity” are subjective and open to broad interpretation. Another major point of confusion is that some of these carb calculators ask you to calculate per KG of bodyweight and others use POUNDS and again there is a whopping difference beween 3g per kg of bodyweight and 3g per pound of bodyweight… I am pedantic. I like exactness and I loathe grey areas. I’m a lawyer, after all, not a politician.

The Bottom Line: Even when you do the maths – tap in your sex, age, gender, weight, height  – to work out your approximate daily carbohydrate needs, there are variable factors that also need to be taken into account that will effect your daily carbohydrate target, such as the intensity and duration of your run/ workout for that day.

BUT WHAT YOU REALLY NEED TO TAKE FROM THIS (other than the fact that I have OCD tendencies and a weird dislike of grey areas!) is that runners do need carbohydrates. Vegetarians, omnivores, vegans, pescatarians, paleo peeps, whatever foodie lifestyle you follow, if you run, and in particular, if you’re training for a marathon or doing other endurance training, your muscles need carbohydrate. So eat em.

In the next episode of this series, I will be looking at different sources of carbohydrates and the types of carbohydrates I eat during training Vs. what should be eaten…

Do you find that you eat a lot of carbohydrates when marathon training or doing a lot of running mileage?

Do you ever bother to do the maths to work out how much carbohydrate you should be eating or do you just eat depending on how you feel?


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