Altitude: the weight you lose there is not real

A fighter arrives at an altitude camp, and in the first week the scale drops 2 kilograms. It looks like the cut is ahead of schedule. It is not. Almost none of that is what he thinks it is, and planning around it is how people arrive at a weigh-in with the arithmetic wrong.

What altitude actually does to a fighter

Most athletic altitude work happens between about 1,600 and 2,400 metres. Above roughly 3,000 metres you are into mountaineering territory, where the effects are different in size and kind.

The camps and the venues that matter in combat sport sit in the first band, and so does everything below.

• Fluid leaves faster. Respiratory water loss rises because the air is dry and you breathe more of it, and there is a diuresis in the early response to altitude. Both happen before you have trained.
• Thirst is blunted. The signal that would normally correct the loss is weaker exactly when the loss is larger.
• Appetite falls. Reliably at higher elevations, and often at moderate ones. Nobody decides to eat less, it simply happens.
• Resting metabolic rate rises. More energy is being spent while less is being eaten.
• Iron demand rises. The adaptation you came for is the production of red cells, and that requires iron.

Why the scale lies

Add those together. More fluid out, less fluid in, less food eaten, more energy used. The number falls quickly in the first days and keeps falling gently after that.

A fighter reading that as progress makes two errors at once. He thinks he is further through the cut than he is, so he relaxes. And the weight he has lost is substantially fluid, which returns when he goes back down to sea level, usually within days.

The collision nobody plans for

Everything above is background. What follows is the reason I wrote the page.

You are in an environment that increases fluid loss and reduces thirst. A weight cut is a procedure that deliberately removes fluid. Running the second inside the first means starting from a deficit you did not measure, with the warning system turned down.

So: no acute water cut at altitude. If the weigh-in is at altitude and the cut is unavoidable, it needs to be smaller than it would be at sea level, and the recovery afterwards has to account for the ongoing losses that continue whether or not you are competing.

The general protocol is in rehydration after the weigh-in, and at altitude the volumes go up rather than down.

Fluid, in numbers

Published guidance puts daily fluid requirements during altitude training and competition at around 4 to 5 litres. Other recommendations describe it as roughly one to one and a half litres above whatever you would drink at sea level.

Two practical points sit underneath those figures.

• Sodium with it. Fluid without sodium passes through you. Glucose and sodium are absorbed together across the gut wall and water follows them, which is why an oral rehydration solution outperforms plain water here as anywhere else.
• Measure rather than feel. Because thirst is unreliable here, the useful habit is a daily morning weight in a consistent state. Day-to-day changes at altitude are largely fluid, which makes them a serviceable hydration signal.

Do not over-correct either. Drinking enormous volumes of plain water is its own problem, and the target is normal fluid balance rather than maximum intake.

Iron, and why it has to be settled before you go

The adaptation altitude is meant to produce depends on making red cells, and that draws on iron stores. If those stores are already low, the adaptation is impaired and you have spent 3 weeks somewhere uncomfortable for less than you paid for.

The important part is the timing. Iron status should be assessed and corrected before departure, not during the camp, because replenishment is slow.

And where stores are already adequate, there is no established benefit to supplementing on top.

That makes this a blood test and a conversation with a doctor, weeks in advance. Not a decision to start taking something because you are going up a mountain. The wider case, including why guessing at iron is a bad idea, is in iron, which applies to male athletes here just as much.

The iron dose-response, which settles the argument

The section above says iron has to be settled before you go. One figure makes it non-negotiable rather than advisable.

Athletes spent about 3 weeks at moderate altitude on different daily doses of elemental iron. The change in haemoglobin mass, which is the entire reason for going, tracked the dose.

Read the top row. Without iron, the adaptation is close to nothing. Three weeks at altitude, the cost of getting there, the disruption to the camp, for just over 1 percent.

The practical version, from the review of nutrition and altitude: blood taken 4 to 6 weeks before the camp, ferritin brought into a workable range before departure rather than during, and 100 to 200 mg of elemental iron daily starting 2 to 3 weeks out and continuing throughout.

Monitoring continues while you are there, because excess free iron raises oxidative stress and more is not better past the point of sufficiency. That is a conversation with a doctor rather than a decision to make from a website, and it is one of the few things on this site where I would not proceed without blood work.

Eating when you do not want to

Energy needs go up while appetite goes down, which is the least convenient combination in nutrition. The consequence is low energy availability arriving by accident, in a camp that was supposed to make you better.

What works in practice is structure rather than willpower: eating to a schedule rather than to hunger, more frequent smaller occasions, and carbohydrate prioritised because it is what the training runs on. Run the figure on the energy availability calculator in the first week rather than the last, and the thresholds are in how many calories does a fighter need in camp.

One honest caveat. At these moderate elevations the specific macronutrient guidance is not well established, and the sensible default is to keep sea-level targets and make sure you actually hit them, which is harder than it sounds when nothing is appetising.

Competing at altitude rather than training there

Different problem. Mexico City sits at around 2,250 metres, and it is not the only venue where a fight happens well above sea level.

If you arrive and compete quickly, you get the fluid losses and the appetite suppression without any of the adaptation, because the adaptation takes weeks. The practical answer is the same as for any travel: decide early whether you are arriving long enough to adapt or short enough to compete before the environment catches up with you, and the framework for that decision is in competing abroad.

And weigh yourself in the same state as at home for the first 2 days, expecting the number to move for reasons that have nothing to do with your camp.

What altitude is actually worth

For endurance athletes the case is well established. For a fighter it is more mixed, because combat sport is not decided by maximal aerobic capacity alone, and 3 weeks in a place where you eat badly and sleep worse has a cost that has to be set against the benefit.

What I would say is this: altitude is a training decision, not a weight decision. The moment it becomes part of a plan to be lighter, it is being used for something it does not do, and the numbers it produces will mislead the person reading them.

Training somewhere new also changes your latitude and your sun exposure, which matters more than most fighters assume: vitamin D.