Phosphorus, an Anti-Obesity Agent? 3x375 mg With Each Meal Strip Almost 4 cm Off Obese Waists in Only 12 Weeks

You knew that all these fat burning high protein foods are high in phosphorus?!

1 cm per week? What sounds like an advertisement for the next best useless fat burner, is in fact the rate at which the 47 obese, but otherwise "healthy" subjects in a recent study from the American University of Beirut had to tighten their belts (Ayoub. 2015)... Ok, I know that this is not DNP-like earth-shatteringly fast, but in view of the fact that the placebo group had to loosen their belts to accommodate for an additional 0.36 cm increase in waist circumference, it is still quite amazing. I mean, would you have expected that the amount of phosphorus of ca. 300 g salmon would have such an effect if there's no other difference in diet or physical activity between the two groups of overweight participants?
Speaking of which,... there were 47 participants (placebo group n = 21; phosphorus group n = 26), 16 men and 31 women, who completed the intervention over the course of all subjects were requested to take three tablets that contained either 375 mg phosphorus or a placebo (Nutricap Labs, Farmingdale, NY, USA) with each main meal (breakfast, lunch and dinner) for 12 weeks (there were no detectable differences in size or weight between intervention and control envelopes | see Table 1).

Table 1: Overview of the baseline characteristics of the subjects in the placebo and phosphorus group (Ayoub. 2015).

Otherwise, the subjects had to maintain their regular dietary and (sedentary) physical activity habits. Whether this was actually the case, however, was unfortunately not monitored by the scientists -- I know that's a bummer, but it is (a) very unlikely that the subjects suddenly started to work out, when they were asked not to, and (b) unrealistic to assume that any effects on the diet that would not be a consequence of the phosphorus supplementation would occur only in the treatment, but not in the active treatment group. Changes in dietary intake that may have occurred in response to the phosphorus treatment, on the other hand, must be expected to occur in the real world as well and would thus only add to the practical relevance of the study at hand compared to a study, where the diet was standardized and potential effects on appetite intake could not have been measured, anyway (as we are going to see further down, this is actually an important fact, even though it would still be nice if we had at least data from food logs).

Figure 1: Weight, waist circumference and serum phosphorus levels expressed rel. to baseline (Ayoub. 2015).

If you look at the selected study outcomes in Figure 1 (please note the non-existing effects on serum phosphorus!), it is still sad that Ayoub et al didn't at least tell their subjects to run food logs, because now everything we have as a basis to speculate about the mechanism that triggered the 'weight and waist loss' are the highly unreliable appetite scores in Table 2; and the latter clearly suggest, but certainly don't prove that the effect was the result of a mere reduction in energy intake.

Table 2: Changes in subjective appetite scores from baseline to 12 weeks (Ayoub. 2015).

Since we don't have those food logs, though, we will have to rely on older studies and a few assumptions to make sense of the results. Well, then...

• there's firstly the evidence from observational studies linking high protein, high dairy and high whole grains intakes to reduced risk of overweight and metabolic syndrome - since a high intake of all three of these food groups is also associated with an increased intake of phosphorus, that's the first line of evidence which supports a mechanistic role of increased phosphorus intakes in weight management,
• there's secondly epidemiological evidence showing an inverse association between an individuals phosphorus status and his or her body weight and waist circumference, and 
• there's thirdly the well-known effect of phosphorus on ATP production, especially in the liver, of which previous studies suggest that it regulates afferent neural signals to the central nervous system which will result in a reduction in food intake (Friedman. 2007).

If we take all three lines of evidence into consideration, we are yet back to square one: the most likely, but unproven mechanism by which the addition of phosphorus to the diet helped the obese subjects in the study at hand lose weight is a reduction in energy intake.

Figure 2: In a previous study the addition of 500mg of phosphorus to a non-caloric or caloric pre-load has already been shown to significantly reduce the food intake during ad-libitum (pizza) lunch (Obeid. 2012).

The latter, by the way, is not just in line with the subjective appetite ratings of Ayoub's study participants, but also with the results of a previous study by Obeid et al (2012), in which the addition of phosphorus to a water, sucrose, fructose + glucose, or pure glucose preload that was administered before an ad-libitum meal lead to an additional attenuation of food intake (see Figure 3). Against that background it is actually very reasonable to assume that the same effect, i.e. a mere reduction in energy intake, is responsible for the 'weight and waist loss' in the study at hand, too.
References:

• Ayoub et al. "Effect of phosphorus supplementation on weight gain and waist circumference of overweight/obese adults: a randomized clinical trial." Nutrition & Diabetes (2015) 5, e189; doi:10.1038/nutd.2015.38.
• Friedman, Mark I. "Obesity and the hepatic control of feeding behavior." Drug News Perspect 20.9 (2007): 573-8.
• Obeid, O. A., S. Dimachkie, and S. Hlais. "Increased phosphorus content of preload suppresses ad libitum energy intake at subsequent meal." International Journal of Obesity 34.9 (2010): 1446-1448.