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Phosphate loading is based on the fact that in vitro studies have found that higher concentrations of phosphate lead to an increase in 2,3-biphosphoglycerate (2,3-BPG) in red blood cells. 2,3-BPG is one of the various factors that leads to a rightward shift in the oxygen dissociation curve, which can in turn allow for greater muscle oxygen utilization. Studies attempting to determine if phosphate loading increases 2,3-BPG and performance in endurance athletes have been contradictory. However, a wide variety of protocols have been used – for example, 22.2 g of calcium phosphate acutely, 4 g of potassium phosphate for 4 days, or 4 g sodium phosphate for 3 or 6 days. A conclusion that can be drawn from the research is that at least 2-3 days of phosphate loading seems to be required to increase plasma phosphate enough to increase 2,3-BPG to the level required for performance enhancement. If these conditions are met, phosphate loading can increase blood cell 2,3-BPG levels by as much as 25%. Whether or not this leads to an increase in endurance performance is not well established, but it is likely that the change does improve maximal oxygen consumption and peripheral oxygen delivery [1]. Additionally, in one study, phosphate supplementation of 4 g for two days decreased the rating of perceived exertion from endurance exercise [2].
Some older research indicates that phosphate ingestion may also facilitate weight loss. In two placebo-controlled studies on obese women on weight reduction programs, one found that phosphates prevented the decrease in T3 levels and increased metabolic rate, while the other found that phosphate supplementation increased resting metabolic rate but did not cause a statistically significant increase in weight loss [3-4]. Two studies also found that acute phosphate addition to a meal increased thermogenesis in obese women, while one additionally found that there was no effect in lean women [5-6]. Therefore, while it is likely that phosphate supplemenation is useful for weight loss programs in the obese, it is less likely that it is beneficial to those who are already relatively lean.
In conclusion, phosphate supplemenation may be useful to endurance athletes and for weight loss in the obese. The suggested dosing schedule is 4 g of sodium, calcium and/or potassium phosphate daily, although smaller doses may still be of benefit.
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