I am often asked about my nutrition leading up to races. For any important marathon or longer races I follow a strict glycogen depletion/carbohydrate loading (carb loading) diet for a week.

This basically entails starving my body of glycogen (carbs) for 3 and a half days after a long run whilst keeping up with fairly intense training, thereby depleting my glycogen stores, followed by 2 and a half days of easing off on the intensity of training whilst eating plenty (loading up) on carbohydrates.
Carb loading is quite a common term amongst runners, it’s the excuse some of us use to pig out on the good stuff leading up to a race, some tend to carb load before 10k races even though it doesn’t offer any benefits unless it’s over half marathon distance. The idea is that if we fill up on carbohydrates we are filling our glycogen stores, glycogen is our body’s favoured fuel when running at pace and we can only store so much of it so it’s a good idea to make sure we have enough stored. During a marathon, most people’s glycogen stores will deplete at between 17-21 miles unless they take on more during the race in the form of sports drinks or gels, if they’re stores deplete they struggle to keep going, commonly known as hitting the wall.
It has been scientifically proven that the muscles and liver are able to store up to 3 times the amount of glycogen when high levels of carbohydrate consumption are preceded by severe glycogen depletion. The easiest and most obvious way of depleting glycogen stores is to eat no carbs or extremely small amounts. Another way is by performing intense bouts of exercise. The stress of severe glycogen depletion triggers an adaptive response by which the body reduces the amount of carbs it converts to fat, and increases the amount it stores in the liver and muscles as glycogen.
It tends to work well for me during longer ultras but there are downsides:
It’s not easy during the depletion phase, I get hungry, irritable, feel terribly weak and lethargic, and can’t seem to concentrate on anything. I am very strict and whereas some athletes may eat some carbs during this phase, I tend to eat none at all and as a vegetarian I live off eggs, cheese, and nuts for 3 days, during this phase I realise how much I actually love fruit!
Having said this, I absolutely love the loading phase, I usually end my “fast” on a Thursday afternoon if my race is on a Sunday, with a Thai, salad, noodle soup, and pad Thai noodles, then a couple of welsh cakes. I then spend the next couple of days eating porridge for breakfast and including plenty of carbs with meals, potato’s, pasta, or rice. The the night before an Ultra I will have a garlic bread pizza and spaghetti pomodoro from Frankie and Bennys, mmmmmmmmm!
This diet isn’t for everyone, we are all different and what works for some may not work for others, I also don’t tend to have a huge taper before races, a couple of days is enough but some people need more, perhaps a long exhaustive run a week before a goal race followed by a few days of intense training may not be something some athletes are prepared to do.
For me the positives outweigh any negatives and unless it fails me I’ll be sticking to the depletion/loading diet prior to big ultra races..