Carbo-loading: should we really be doing it?

It's still winter in Paris, but many runners here are currently looking to mid-April as they train for the Paris marathon. This feels like a good time to talk about carbo-loading, the time-honoured tradition of eating a lot of carbohydrates before a race to increase energy.

Let's dispel some of the mistakes around this common notion that eating more carbohydrates increases energy and glycogen stores. While there are studies demonstrating the potential for improved endurance performance following carbohydrate loading, which may maximize liver and muscle glycogen storage. But others show that its much more dependant on factors like race distance and the level of aerobic fitness. But overall, most of these studies are performed on young and relatively healthy athletes, an abundant resource on university campuses, and have little regard for trivial things like health.

And these are two major problems. First of all, younger people are much more insulin sensitive (I'll explain why that's important in a second), and then there's the disturbing fact that by not considering health in the equation, we're leaving the door wide open to recommendations that might prove beneficial on a stopwatch the first time, but could lead to health complications down the road.

Let's get into this insulin sensitivity real quick before we get back to our topic. I'll do a more detailed article about this some day, but what's important for us here is that insulin is a hormone responsible a process called "de novo lipogenesis" or DNL, transforming dietary carbohydrates in to lipids (fat), and it also reduces our ability to use our fat stores (lipolysis) while it processes these carbohydrates. Look at it as a kind of switch that make fat go in (DNL) or out (lipolysis) of your body's storage, so when insulin goes down after managing your blood sugar, your lipolusis can resume. This all good if you are insulin sensitive, but if you are insulin resistant, which is pretty much guaranteed to happen as you get older, you will need to produce more insulin during a longer amount of time to process the carbs, therefore keeping your fat burning off much longer. So studying carb loading on younger athletes is an issue because they usually have little problem storing the excess carbs as fat, and it happens rather fast, not stunting their fat burning for too long. Switch to a 40 sometinhg year old that has developed higher insulin resistance due to a high carb diet (like so many athletes in their forties), he/she could essentially have their fat burning stunted most of the time, meaning they have great trouble burning the fat they keep storing, and their pre-race carbo-loading will impair access to their fat stores during the race, focing them keep chugging carbs to keep going, only making the whole thing worse in the process.


Why is this important? Well constant insulin production can lead many health problems like type 2 diabetes and non-alcoholic fatty liver disease (NAFLD), and glycogen is a relatively limited fuel source, whereas fat stores offer seemingly limitless amounts of energy.

Even the leanest of athletes still has 30,000 to 60,000 kcal of fat for potential energy, enough to run hundreds of kilometres. On the other hand, stored carbohydrates, as glycogen, only total about 2,000 kcal, so not even enough for a 42 km marathon. I should add that both fuels are used conjointly, but when I talk about fat burning, I mean that we're getting most of our energy from fat and only a small percentage from sugar (and the opposite when I mention sugar-burning). Put simply, the more fat we use as fuel during exercise, the easier it is to go longer.

So can we carb-load? Well yes, but we have to be very aware of where our insulin resistance is, and choose our carbs and their quantity accordingly. It’s the refined carbohydrates that pose the problem for everyone, while natural ones — fruits, beans, lentils, oatmeal, sweet potatoes — are potentially nutritious based on the individual’s level of insulin resistance.

Unhealthy Carbs

  • Almost all pancakes, muffins, bagels, breakfast cereals, etc.

  • White potatoes, pasta, corn.

  • Sugar and sugar-containing snacks/desserts, bananas, watermelon, dried fruit, fruit juice; sports drinks and energy bars.

Healthy Carbs

  • Stone-ground flour and cereal products like long-cook oatmeal (40+minutes).

  • Lentils, beans, sweet potatoes.

  • Fresh apples, pears, berries, melons, avocados, citrus, peaches, vegetable juice.

  • Honey.


The idea that refined carbohydrate in all its many forms is unhealthy comes with decades of scientific research — laboratory studies, clinical trials and epidemiological analyses — and careful clinical observations. In fact, among what may be the most common population of carbo-loading people — amateur runners — we clearly see that, not only have running race times been slowing down for many years, but physical, biochemical and mental-emotional injuries are very common, including the metabolic problem associated with the overfat pandemic, which has not spared athletes.

This is not to say the use of sports drinks, gels and other carbohydrate supplements during competitive performance is unhealthy or not effective; it is something I recommend, despite personally having better results with natural substitutes like diluted fruit juice. But using these carbohydrates as a down-time snack or part of regular meals can be devastating to human metabolism and one reason carb-loading is dangerous.

So that massive plate of pasta you're shoving down before race day isn't working. It's making you put on additional weight you could easily do without, and is turning off your best fuel source. It just so happens that as people have been getting fatter, in the midst of the overfat pandemic that hasn't spared athletes, the race times have been dropping, as only the elite athletes have been getting faster (

Now that you have this information, are you still going to your next race's pasta party?

Thumbnail credit: unsplash-logoAlice Pasqual