CARBING UP or PEAK WEEK involves eating large amounts of carbohydrates before an event, but is it really worth it?

If you’re involved in endurance sports you may have been told to “carb up” for an event. The theory being, that if you eat a lot of carbohydrates, they will be transported into your muscle to fuel your big day.  Let me tell you from experience, there are so many things that can go wrong here. It took me my first ten years of competing to get this exactly right, so it is very VERY doubtful that an online coach or social media ‘guru’ will nail it for you. Unless you’re working with someone that really knows how to manipulate your nutrient intake, you’re more likely to get it wrong than to get it right. Too many carbohydrates at the wrong time will make you tired, sluggish – and fat. Is carbohydrate loading really worth it?

carbing up yes or no?

Carbohydrates trigger insulin and …

Insulin can take carbohydrates into muscle.

Muscle stores carbohydrates as “Glycogen.”

Glycogen will fuel that muscles activity.


There are a couple of keywords to pay attention to here.

Insulin CAN take nutrients into muscle – but sometimes it CANT

Glycogen will fuel THAT muscles activity – it will not fuel ANOTHER muscles activity.


Glycogen is the form in which carbohydrates are stored in the muscle and the liver. To simplify the terminology

  • Carbohydrates are on your plate
  • Carbohydrates in your blood are called Blood Sugar aka blood glucose
  • Carbohydrates in your muscle (or liver) are referred to a Glycogen.

If we freeze water, we call it ice, if it falls from the sky we call it rain and if we play in it we call it snow.  When substances take different forms, we give them different names.

Never let terminology intimidate you.


There is a limit to how much glycogen a muscle can store.  The larger the muscle, the more glycogen it can hold, and a conditioned athlete can store more glycogen than a normal person.

You cannot put two quarts of water in a one-quart jug.

Muscle is not a bottomless pit. Every muscle has its own storage capacity.

A person may hold between 1500 and 2500 calories worth of glycogen in their muscles, which translates to 7-8 grams of carbohydrates per lean pound of body weight. That is not that much, especially as muscle is rarely empty. Unless you’ve gone to deliberate measures, like doing a 24 hour fast or doing several hours of cardio, your muscles will be storing some glycogen.

In bodybuilding to increase the accuracy of our efforts, we would carb deplete for several days before doing the ‘carb load.’

George eats 3000 calories a day with 85% of his calories coming from carbohydrates (not an unusual occurrence).  That would be 637 grams of carbohydrates per day.

George lives in Los Angeles, drives to work and sits at a desk all day.  George is overweight and is getting heavier every year.  George is eating more carbohydrates than, his muscles can store. Thankfully (not) his fat cells have no such limitations and will happily store excess for George.

Thomas eats 3000 calories a day, 60% of his calories come from carbohydrates, that would be 450 grams of carbohydrates per day.  Thomas lives in New York, walks to work, lifts weights and is in a rowing club.  Thomas is not overweight.

In today’s society exercise is becoming more of an option, perhaps even a luxury. We drive more, our work is less manual and our time is limited. Muscles are not depleted, and eating patterns are carb heavy.

Insulin promotes fat storage, and how we eat and how much we move determines what role insulin plays in our lives. Food will dictate the insulin response and exercise will determine where the nutrients end up.

When you exercise a muscle, you deplete the glycogen stored in that muscle. If we exercise consistently, we create space where new glycogen can be stored. “Exercise” does not mean a gym membership or a pair of running shoes, an active lifestyle requires a lot of muscle activation and so depletes muscle glycogen stores. You don’t see many fat guys doing construction.

After a meal, the amino acids (protein) and blood sugar (carbohydrates) go to your small intestine where blood vessels absorb them and take them directly to the liver. The liver takes up most of the nutrients you just ate, (first pass metabolism) and can store about 100 grams of glycogen. Excess carbohydrates are converted into fatty acids and stored as (you guessed it) fat.

It is liver glycogen that can leave its host, travel in the blood and provide fuel for other bodily functions. Muscle glycogen cannot.

If your blood sugar drops because of missing meals or creating your own food coma, being buff won’t help you

Glycogen is also stored in the liver (about 100 grams) and this glycogen (not muscle glycogen) is used to fuel most of our bodies energy requirements. Liver glycogen is replenished first. Muscle glycogen pretty much stays put until that muscle uses it.  Muscle glycogen cannot help if your blood glucose level drops – only the liver can help with that.

Carbohydrates can be stored in the muscle and liver as glycogen. Both have their own storage capacity. Fat has no such limit. Sugar with nowhere to go will be converted into fatty acids and stored in our fat cells. Fat cells increase in volume to oblige our uninformed choices

A gentleman did his first marathon, gained 10 lb and came to see me. He was furious. He went from inactive to running four days a week. Understandably his appetite increased and was encouraged to eat a lot of carbohydrates to fuel his runs. He gained 10 lb

As a personal trainer, I signed up for a weekend course to be a running coach.  Most of the attendees worked with novice runners, organizing running clubs and charitable events. I learned a lot, but was excited for day two when they were to cover nutrition. I’ll never forget that the module, which should have been an hour and was completed in 15 minutes, was summed up by the instructor (an ectomorph) telling the coaches “get your clients to eat well and running will take care of the rest.”

I would suggest that the majority of people that join a running club do so to get in shape. I would also guess that most recreational runners are not ectomorphs. When the well-meaning, passionate coaches are not given the guidance that they need, then we end up with angry men knocking on my door.

‘Carbing up’ or as it is now called “peak week” may work for you but it can very easily work against you too. If endurance is your game my advice would be if you dont deplete you dont need to carb up. If you’re taking the stage then there is a little more to gain from this type of nutrient manipulation, although more often than not competitors miss their mark by not carbing up and looking a lot better a few days after the show.

Preparation is the best course of action so if you have a competition or event plan to do a practice week about 4-6 weeks before the big day. A practice week will allow you to evaluate results and performance.  Above all, remember your goal, if you’re competing but your ultimate goal is to improve your body composition then carbing up is not likely to move you towards that goal

Until next time




joanne lee cornish

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