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Sodium Phosphate

Also known as: Tribasic sodium phosphate, Phosphate loading, Trisodium phosphate, Dibasic sodium phosphate

EnduranceGood evidence

One of the better-evidenced endurance aids that almost nobody sells. Phosphate loading has been reported to improve VO2 max and time trial performance across several decades of research.

Typical dose

3.0–4.0 g per day

3-6 day load before the event, split into four daily doses with food

What it is

Sodium phosphate is a simple mineral salt, used widely as a food additive and, in a specific loading protocol, as an endurance aid.

Phosphate is central to energy metabolism. It forms part of ATP and phosphocreatine, and of 2,3-DPG, the molecule inside red blood cells that governs how readily haemoglobin releases oxygen to tissue.

Research on it dates back to the 1980s and it has been studied repeatedly since, which makes its near-total absence from the commercial market genuinely odd. It is cheap, unglamorous and difficult to brand.

How it works

Phosphate loading increases 2,3-DPG in red blood cells, which shifts the oxygen dissociation curve so that haemoglobin gives up oxygen more readily at the tissues that need it.

It also increases the availability of phosphate for regenerating ATP and phosphocreatine, and contributes to buffering capacity.

The oxygen delivery mechanism is what distinguishes it from the buffering agents in this index. Bicarbonate and citrate help clear hydrogen ions; phosphate improves how much oxygen actually reaches working muscle.

What the evidence shows

Multiple controlled trials have reported improvements in VO2 max, typically in the region of 5 to 10 per cent, alongside better time trial performance in trained cyclists and runners.

Findings have been reasonably consistent across independent research groups over several decades, which counts for a good deal.

Not every trial has found an effect, and study sizes are generally small. The protocol also matters: results depend on a specific loading regimen rather than casual daily use.

Dosing

The researched protocol is 3 to 4 g daily, split into four doses, for three to six days before the event. It is a loading protocol rather than a daily supplement. Take each dose with food to reduce digestive upset, which is the main practical complaint. The effect appears to persist for several days after loading stops, so timing the load to finish a day or two before competition is the usual approach. Effects diminish with repeated loading close together, so it suits key events rather than every race. Trial it in training first, since digestive tolerance varies.

At a glance

Common forms	Tribasic sodium phosphate, Dibasic sodium phosphate, Sodium phosphate capsules
Half-life / duration	Effects persist for several days after loading ends
Timing	3-6 day load before the event, split into four daily doses with food
Competition status	Permitted — not on the WADA Prohibited List
Category	Endurance

Safety and side effects

Digestive upset is the main reported effect, including nausea and loose stools, and taking each dose with food reduces it considerably.

The sodium load is worth counting if you are managing intake.

Phosphate handling depends on the kidneys, so anyone who has been told their kidneys are not working normally should avoid this entirely and speak to their doctor. It also affects calcium balance, so prolonged or repeated loading is unwise.

Who should avoid it

Avoid entirely if you have been told your kidneys are not working normally, and speak to your doctor first. Take care if your blood pressure is being managed, given the sodium load. Use as a short load rather than continuously, since prolonged use affects calcium balance. Trial in training before competition. Speak to your doctor before use if you take regular medication.

This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.

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