Carb loading before a gran fondo: how to do it properly

Carbohydrate loading is one of the few pieces of sports nutrition that genuinely earns its reputation. Muscle glycogen is the limiting fuel in long, hard endurance events, and you can meaningfully increase how much of it you start with. For a gran fondo — four, five, six hours, with climbs — that is worth real minutes.

It is also one of the most badly executed. Most riders either do nothing and hope, or do a version of a protocol from the 1960s that nobody has recommended for forty years. The modern approach is shorter, easier and takes about two days.

What you are actually doing

A trained cyclist stores somewhere in the region of 400–500 g of glycogen across muscle and liver in a normal fed state. Loading properly can raise muscle glycogen substantially above its usual concentration — the phenomenon called supercompensation, first demonstrated with muscle biopsies in the 1960s.

That extra fuel does not make you faster. What it does is delay the point at which you slow down. In events lasting beyond about 90 minutes, and increasingly as they get longer, running low on glycogen is the thing that turns a strong ride into a survival exercise. Loading pushes that point further out.

It follows that for shorter events — a one-hour criterium, a 40 km time trial, a hilly two-hour club run — loading is largely pointless. You will not run out, and you will have paid the weight cost for nothing. Simply eating normally with adequate carbohydrate is sufficient.

The old way, and why it is gone

The numbers

The target is around 10–12 g of carbohydrate per kilogram of body mass per day, for one to two days before the event, while training almost nothing. Both parts matter: the intake is only achievable if you are not also riding, and the loading only works if the carbohydrate is not being spent as fast as it arrives.

That last point is the single most common failure. A big plate of pasta the night before is perhaps 150 g of carbohydrate. It is a nice dinner; it is not a carbohydrate load. Hitting 700 g means carbohydrate at every meal, plus snacks, plus drinking some of it — which is why juice and sports drink appear on every practical list. Solid food alone runs into a volume problem long before it runs into a carbohydrate one.

Yes, you will get heavier

Glycogen is stored with water. The classic figure is around 3 g of water per gram of glycogen, and while the exact ratio is debated and varies with method, the direction is not in question. A successful load typically shows up as 1 to 2 kg on the scales on race morning.

This alarms people, and it should not. It is not fat, it is not bloating in any pathological sense, and it comes with the fuel you actually wanted. It is, however, a genuine cost rather than a free lunch: on a very mountainous event the extra mass works against you, and for the shortest events the arithmetic can tip the other way entirely. For a long fondo where the risk is fading in the final hour, carrying the fuel is almost always the better trade.

What to eat, and what to leave alone

Two practical notes. First, keep fibre low during the loading days. High-fibre food is exactly what you want in an ordinary week and exactly what you do not want when you are trying to fit 800 g of carbohydrate into a day and then ride hard. Second, protein and fat do not disappear — you are raising carbohydrate, not eliminating everything else. Just accept that both will be proportionally lower for two days.

What it feels like

Unfamiliar, and slightly unpleasant. Expect to feel full, heavy and faintly sluggish, to be visibly a bit puffier, and to find the last few hundred grams a chore rather than a treat. Some riders sleep worse. Almost everyone feels slower on the morning of the event than they did three days earlier — which, combined with a taper, produces a very specific kind of pre-race anxiety.

This is why the advice to practise it once before a goal event is not optional. Do a full load before a long training ride, a month or more out. You will learn whether the volume of food causes you trouble, which foods work, and what the sensation is — so that on event morning, feeling heavy reads as "it worked" rather than "something is wrong."

A workable two-day plan

• Two days out: very light riding or nothing. Start eating to target from breakfast. Reduce fibre.
• The day before: short easy spin at most — 30 to 45 minutes with a couple of brief openers, if you like riding the day before. Hit the target again. Drink to thirst plus a little, since glycogen storage takes water with it.
• Race morning: a familiar breakfast, roughly 1–4 g/kg of carbohydrate depending on how early and how much you tolerate, finished around three hours before the start. This is topping up liver glycogen after the overnight fast, not continuing the load.
• During: keep eating. Loading extends your range; it does not replace on-bike fuelling. A five-hour fondo still wants 60–90 g of carbohydrate an hour.

Whether it is worth doing at all comes down to how long you will actually be out there, which is usually longer than riders estimate for a mountainous route. Moveee's Route Engine gives you a realistic duration and elevation profile from the actual course, and the plan handles the taper alongside it — so the question becomes an arithmetic one rather than a guess.

Carb loading is not a secret weapon, and it will not rescue a season of undertraining. But it is one of the few pre-event interventions with decades of consistent evidence behind it, it costs nothing beyond groceries, and most riders leave it on the table entirely.