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Carbohydrate intake for Crossfitters: Part 1 - ICON Nutrition

Carbohydrate intake for Crossfitters: Part 1

Carbohydrates have a mixed reputation, depending on which guru you listen to, which websites you follow or your own general view on nutrition, your ideas about carbs are either positive or negative, some view them as essential others claim they are not.
From a technical point of view, they are not essential as the body can function without them and we can fuel the body with other sources on energy (fat, Ketones). Crossfit HQ’s view on carbs is to eat enough to maintain performance, but not enough to cause fat gain, with the sweet spot being about 40% of calories coming from good quality carbs.
But as we know, there is never a one size fits all approach to nutrition, so a little bit of detective work is required to find your own individual sweet spot which improves both performance and body composition.  

Introductions: What are carbs and why do we need them?

Carbohydrates are forms of starches / fibres and sugars that are broken down in the body and turned into glycogen (the muscles store of carbohydrates), or glucose, which circulates round the body via the blood and feeds the brain, muscles and other important organs with energy. The conversion of carbohydrates into fat (known as de novo lipogenesis) is actually pretty inefficient in humans and requires a massive carb overfeed over several days (1). So carbs being directly stored as fat is pretty unlikely, but they do still influence fat storage indirectly, more on this to come.

When we are training, we either use energy from acute nutrition (i.e meals) or previously stored energy in the form of glycogen within the liver and muscle tissue. When it is needed it is converted into glucose that is then used as the energy to set off a chain of reactions that occur to split ATP to ADP which then in turn provides the energy needed to power our heavy lifting and WOD’s.

Fuelling our WOD’s

There is one word that summaries Crossfit perfectly and separates it from many other forms of training: INTENSITY. You cannot perform Crossfit without intensity, and if you did, then put simply it wouldn’t be Crossfit. Due to this, Crossfitter’s rely pretty heavily on anaerobic glycolysis (ie breaking down carbs into energy without oxygen). This system ‘kicks in’ as soon as high intensity work starts to take place, events that last from 30 seconds to about 4 minutes get the energy that is needed to make the muscles contract when the glucose (carbohydrate) is broken down without the use of oxygen.

The higher the intensity of the exercise, the more the body looks for carbohydrates to use to fuel the body for the session. The reason for this is because during the high intensity exercise (this being anaerobic due to the lack of oxygen) the ATP-PC system and the anaerobic glycolytic system are the systemst are in use. Things like Squat clean ladders, sprinting, strength and power training, Tabata use more of the carbohydrates (in the form of muscle glycogen) than they do fat that has been stored. As the sessions get a little longer (longer AMRAPS, longer monostructual) we use different energy pathways to provide energy to the working muscles, the body uses a combination of carbohydrates and fats for fuels, but can also use protein during extensive exercise. During lower intensity exercise the body relies more on fat, while during resistance and interval based exercise the by uses more carbohydrates.


Key Point: The Higher the intensity the more carb’s that are being used to power the session 

Factors that influence carbohydrate

Like all areas of performance nutrition, carbohydrate intake is down to the individual with no universal one size fits all approach that will work for everyone. The key is to find a starting point for carb intake and adjust this number up or down according to the results you are achieving: flexibility is the key. There are a number of factors that will affect your initial starting point for carb intake, either as an absolute value of relative to fat and protein.

●Body size: The bigger you are the more you need
●Body fat percentage: The lower your body fat percentage, the better your insulin
sensitivity and the better your body handles carbs.
●General physical activity levels, physical job: The higher they are the higher carb
intake could be.
●Training volume: The Higher your training volume, the higher your calorie and
carb intake should be.
●General tolerance of carbs: If they make you feel sluggish, lower concentration
make you look puffy or hold water, then lower amounts and timing of carbs may
be useful, if you feel energised, focused, fuller and pumped after eating a lot of
carbs then your likely more tolerant to them.

Key Point: All of these factors will influence a starting point to set an initial carbohydrate intake: the key is to adjust this target according to your response, results and performances

Carb intake and your goals

One of the understated benefits of Crossfit is its ability to effectively change body composition for the better, regardless of if it is used as exercise or sport (2). This means with some tweaks to your training and tailoring your diet accordingly we can use Crossfit to improve body composition well as fitness.

Fat Loss

The most important factor regarding fat loss is a calorie deficit, from there, how those calories are reduced is down to the individual, but for us Crossfitter’s creating this calorie deficit by purely reducing carbs will ultimately lead to decreases in performance and impaired recovery if a high training volume is maintained.

Carbohydrates are the bodies preferred fuels source as they provide energy easily to the body whereas fat metabolism takes longer to get the energy required to fuel our activity but provides more energy when it is being burnt. When carbohydrates are eaten they
increase insulin levels to help reduce blood sugar levels by pushing amino acids and blood sugars into our muscles and fat cells. When insulin levels are high the bodies prime fuel source are carbohydrates and the body will turn off fat burning and direct
incoming dietary fat towards storage and away from burning. For this reason carbohydrates may have an indirect effect on fat storage as a high intake of carbohydrates will make it more difficult to burn in coming dietary fat and harder to release stored body fat from our stores to be burnt. It is extremely important to note however that carbohydrates alone do not make us fat as the body is extremely inefficient at converting dietary carbohydrates to body fat. Dietary fat can be stored easily by the body when to many calories are eaten then we need, even when carbohydrates intake is low (3).

●Fat may cause body fat gain directly by being stored straight into fat cells when
we eat in excess
●Carbohydrates may cause fat gain indirectly by preventing dietary fat from
being burnt, making it easier to be stored and harder for it to leave fat cell to be
●Fat storage and burning occurs after every meal and is a constant process
●A combination of high carbohydrate and high fat will lead to more fat storage
and less fat burning (4)
●Both high carbohydrate low fat diets and low carbohydrate higher fat diets can
be effective for weight loss (5,6)
●Which approach is most effective is down to the individual, those shown to have
high insulin sensitivity appear to lose weight more efficiently with a higher carb
intake, those with lower insulin sensitivity seem to do a little better with a lower
carb intake (7). A recent meta-analysis showed that provided calorie content of a
balanced diet and low carb diet is matched, fat loss is similar (8). This is good
news for crossfitter’s as it means we don’t need to drop carbs too low to lose fat,
which has been repeatedly shown to impair exercise performance at high
intensities (9)
●Reducing carbs too low for extended periods of time can have negative effects on
the hormonal system, which has a knock on effect on health and performance;
this can be magnified when high intensity exercise is added to equation. Thyroid
function can be impaired effecting metabolism and energy, leptin levels can fall,
this is a anti starvation hormone that helps to control hunger and metabolism
(10), when leptin is low the body sense this as we are starving so decreases
metabolism and increases hunger (11). The stress hormone cortisol increases to
help mobilise energy, this can cause muscle break down, inflammation and
impaired recovery from training, over extended periods of time this can stress
the adrenal glands leading to greater issues, especially if combined with a
stressful lifestyle and excessive stimulant use (12).

Muscle Gain:

It also doesn’t hurt to gain a little muscle, especially if it transfers to improved strength and power, while not having a negative effect of endurance or power to weigh ratio. Carbs are also pretty important for gaining muscle, not only do they provide a hefty source of
calories, but insulin is required to help build muscle and prevent muscle breakdown, and although protein can provide similar effects, with regard to preventing muscle breakdown, carbs provide a solid basis for building some muscle. Muscle glycogen levels acts as an anabolic
signal, so starting a session with low levels of glycogen makes it difficult to get a positive anabolic response from resistance exercise and could potentially hinder muscular gains (13). This is due to an increase in AMPk (Adenosine monophosphate-activated protein kinase, which is a signalling enzyme that acts as a fuel gauge and tells us how much fuel is available), this is good for endurance and fat burning but bad for muscle building as the body won’t build calorifically expensive tissue (ie muscle) if the body thinks energy is in short supply, this is one possible reason why it is difficult to lose fat and build muscle at the same time and why carbohydrates are important when looking to increase muscular gains (14).

When looking to gain weight it is important to matching carb and calorie intake training volume
while also creating a calorie surplus: A starting point for calorie intake maybe :

●20 calories per pound of body weight: to provide calorie surplus
●Additional 20 Calories per round or minute of the WOD

Obviously, these numbers are only a starting point and would be adjusted accordingly, but they
provide an example of how adjust calorie and carb intake in relation to training volume. The
numbers aren’t set in stone and a certain amount of trial and error is required until you hit the
sweet spot, both from a starting point and by how much to adjust calories by.

Competition Double sessions of Competition days

This is when carbs become pretty much vital, as previously mentioned, Crossfit stresses the glycolytic system pretty heavily to help power our sessions, this burns through a ton of glycogen due to the high intensity nature of the sport. If you are training more than once a day or there are less than 8 hours between sessions or events, then the type and timing of carbohydrates becomes more important for recovery to fuel future training or the next competition WOD. This is where fast digesting carbohydrates provide the most benefits and replenish the most muscle glycogen in the shortest period of time (15) the amount of glycogen stored can be improved by including the following ingredients with your carbs post training .

●Whey protein
●Caffeine (based on individual tolerance)

A general guide for post training carb intake for double training session would be 1g of carbohydrate per kg of bodyweight with 0.5kg of protein per kg of body weight (16) although volume and type of session would also influence these values, the number of meals / length of time between sessions must also be taken in to account. The longer the time or more meals between sessions, the smaller the carb intake can be per meal as long as the same total amount of carbohydrates is consumed between sessions, this is down to individual preference and tolerance of training on a full stomach, completing Fran after a large meal isn’t a great idea


●Crossfit relies heavily on the glycolytic energy system and high volume WOD can burn through a lot of carbs ●Carb intake is unique to the individual with many factors affecting your overall intake; this could vary day to day.
●Provided calories are matched, it appears low carb diets offer no additional benefits to fat loss compared to a balanced diet, the perfect scenario for a crossfitter’s is to keep carbs / calories as high as possible while still losing body fat and adjusting these as plateaus are reached.
●Carbs help with muscle gain by providing calories and acting as an anabolic signal within muscles as well as aiding training intensity, if still including a lot of met cons, aim to match carb and calorie intake to training volume.
●When training more than once per day or at competition, ensuring carbs are eaten between sessions or events helps maximise recovery when time is a limiting factor
Part 2 will focus on when to eat your carbs to help improve recovery, performance and body composition


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10.Wesche MF, Wiersinga WM. Relation between lean body mass and thyroid volume in competition rowers before and during intensive physical training. Horm Metab Res. 2001 Jul;33(7):423-7 11.Crujeiras AB, Goyenechea E, Abete I, Lage M, Carreira MC, Martínez JA, Casanueva FF. Weight regain after a diet-induced loss is predicted by higher baseline leptin and lower ghrelin plasma levels. J Clin Endocrinol Metab. 2010 Nov;95(11):5037-44.
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About the Author: Paul Johnson

​​Paul holds and BSc in Sport & Exercise Science and MSc in Exercise & Nutrition Science, while being accredited by the SENr (Sports & Exercise Nutrition register). He works full time as a Exercise referral specialist working with cardiac rehab, COPD, chronic pain patients. While coaching both training and performance nutrition to functional fitness and indoor rowing athletes online , While as an athlete himself he has competed in Crossfit and currently hold 4 British Indoor Rowing records.

You can find him:
Instagram : @lreg_fitness_and_nutrition
Facebook: Lift Row Eat Grow