ORS for athletes: why the sachet works and the sports drink does not

An oral rehydration solution, or ORS, is a fixed ratio of sodium, glucose and water built to be absorbed faster than water on its own. For an athlete coming off the scale it is the first thing that should go in, and a sports drink is not a substitute for it.

Every rehydration protocol in this sport says the same first line: oral rehydration solution, not plain water. Almost nobody explains why, which is how fighters end up sipping a sports drink and wondering why they still feel flat 2 hours later.

The answer is one mechanism in the gut wall. Once you know it, every product decision in this article makes itself.

What a cut actually removes

A weight cut does not take water out of an otherwise unchanged body. Sweat carries sodium with it, and how much varies enormously between people: reported concentrations run from around 10 to over 90 mmol per litre, with most athletes somewhere in the 20 to 70 range. A salty sweater can lose 4 or 5 times the sodium of a fresh one from the same session. Food restriction removes potassium and magnesium at the same time, so by the time a fighter steps on the scale several systems are short at once.

Which is why drinking a litre of plain water immediately afterwards makes things worse before it makes them better. Fluid without sodium dilutes what is left in the blood, and the body responds by getting rid of it. In extreme cases the result is hyponatremia. In ordinary cases the result is a fighter who drinks 2 litres, urinates most of it, and cannot understand why he still cramps.

The mechanism, in one paragraph

The gut wall has a transporter that moves sodium and glucose across together. Neither goes efficiently without the other. Water follows them by osmosis, so the rate at which you rehydrate depends on how well that transporter is being fed.

Feed it correctly and absorption is fast. Give it water alone and there is nothing to carry. Give it a sugary drink with almost no sodium and the transporter has half of what it needs, while the excess sugar draws water the wrong way, into the gut.

This is the entire reason oral rehydration therapy exists. In 1978 the Lancet called the discovery behind it potentially the most important medical advance of the century, which is the sort of sentence a medical journal does not write often.

What is in an ORS sachet

The formulation WHO and UNICEF have recommended since the early 2000s, per litre of water:

In weights, that is roughly 2.6g of sodium chloride, 2.9g of trisodium citrate, 1.5g of potassium chloride and 13.5g of glucose per litre.

Note the ratio. Sodium and glucose are equal. That is not a coincidence or a rounding: it is the transporter being fed in the proportion it uses.

An older WHO formulation ran at 311 mOsm/L with more sodium and considerably more glucose. It was replaced because the lower-osmolarity version worked better.

If a product on your shelf is quoting the older numbers, it is quoting a superseded standard.

Why a sports drink is not this

Clinical guidance is unusually direct on this point. Sports drinks, sodas and juices are not recommended for rehydration because they generally contain too little sodium and too much carbohydrate to use sodium-glucose cotransport properly, and the excess sugar works against absorption.

A typical sports drink carries sodium at a fraction of the concentration in an ORS. It was designed for a different job: replacing fluid and fuel gradually during 90 minutes of running, in an athlete who started the session hydrated.

A fighter who has just made weight is not that athlete.

The tablet that is right before the scale and wrong after it

Look at what a fight-week protocol asks for and you will find a contradiction that nobody explains.

During the cut, the instruction is an electrolyte tablet with no sugar, dissolved in the water allowance. Correct: you are not trying to absorb fluid quickly, you are trying to hold electrolytes while restricting fluid, and sugar adds gut content and calories you do not want on the scale.

Thirty seconds after the scale, that same tablet is close to useless for the job in front of you. Without glucose there is no cotransport, and cotransport is the entire point of the first half hour.

This is the moment for a proper ORS, not for the thing that got you through the last 2 days.

Two products, two jobs. Carrying only one of them is the mistake.

How much, and the number that gets misread

Position statement guidance for reversing a moderate to severe deficit quickly puts total fluid at up to 150 percent of what was lost, because losses continue while fluid redistributes.

Lose 2 kilograms, plan for around 3 litres across the window.

That figure is a target for the whole recovery period, not an instruction for the first hour. Drinking 3 litres quickly does not rehydrate you 3 times faster, it produces urine and nausea. The full hour-by-hour structure is in the rehydration article, and the rules each organisation enforces around it are in rehydration rules.

One thing that is not an option: an intravenous drip. Infusions above a defined volume in a 12-hour window are a prohibited method regardless of what is in the bag, which is covered separately in IV drips after the weigh-in.

Buying the stuff

Electrolyte products are supplements, and they carry the same contamination exposure as anything else you put in your body. The category is lower risk than fat burners by a wide margin, but low risk is not no risk, and strict liability does not scale with how boring the product is.

• Buy from a programme register rather than from a shelf. Which register depends on where you are, and the three that matter are compared in the certification article.
• Read the sodium figure on the label, not the marketing. If it is not stated in a way you can compare, that tells you something.
• Pharmacy rehydration sachets are often the cheapest way to get the correct formulation, and they are made to a medical standard. Check them like any other product.
• Log the lot number of whatever you take in fight week. It costs 10 seconds and it is the difference between evidence and memory.

The bit nobody packs

Every fighter I have worked with has owned electrolytes. A smaller number have owned the right one for the right moment. A smaller number again have had it physically in the bag at the venue, mixed and ready, rather than in a cupboard at home.

The protocol for the first 30 minutes after the scale is simple and unforgiving about preparation, because those 30 minutes happen once and you cannot go shopping in the middle of them.

Pack two sachets. You will use one.

Magnesium is the other name that comes up whenever cramp does, and the evidence behind that claim is far thinner than the sodium story. That is set out in the magnesium article.

You cannot replace what you have not measured, and your own losses take one session to establish: measure your own sweat rate.

Athletes managing insulin have their own version of this problem, set out in training and competing with type 1 diabetes.