Fried bacon. A grilled cheese sandwich. Self-basting turkey. A muffin. Ice cream. A can of tuna. A cola drink. What do they have in common besides frequently cropping up in the western diet? They all contain some form of phosphate additives. And that is turning out to be an issue. Too much phosphate in the diet may have health consequences, particularly as a risk factor for heart disease.

This possibility may be surprising because phosphates are also essential for health. They are a component of DNA, the “blueprint of life,” as well as of adenosine triphosphate, ATP, the key molecule in the cell’s production of energy. Phosphates are components of phospholipids that make up cell membranes and calcium phosphate is the main building block of bone.

There is no problem in meeting the body’s needs, because various phosphates occur naturally in plants and animals. Plants get their phosphate from the soil and animals get them from plants. Soil phosphate has to be replenished, making phosphate fertilizers produced from phosphate-containing rocks an essential feature of modern agriculture. They are not without problems, because phosphate washed into lakes and rivers increases plant growth and when these plants die, they decompose and use up the dissolved oxygen content of the water, robbing fish of the oxygen they require for life.

Phosphates in plants are integral components of molecules such as phospholipids and DNA and are liberated during digestion to be absorbed and used to build the body’s requisite phosphate-containing compounds. We have evolved to absorb only the amount of phosphate needed; the rest is eliminated in the urine and feces. Indeed, the first problem with phosphates cropped up in patients with kidney problems who suffered from a high rate of cardiovascular disease that was traced to high serum levels of phosphate, a consequence of their kidneys being unable to filter excess phosphate. Excess phosphate combines with calcium in the bloodstream to form deposits of calcium phosphate in arteries, leading to a “hardening” of these vessels. The prevailing opinion has been that this is only a problem for kidney patients who therefore have to maintain a low-phosphate diet because their kidneys cannot clear phosphates efficiently.

However, recent studies have shown that excess phosphate may also be a problem for people with normal kidney function. One study even found hardening of arteries in young men with high serum levels of phosphate. This seems to be the result of the high phosphate levels reprogramming smooth muscle cells in blood vessels to become bone forming cells. The puzzling question is how people with normal kidney function end up with high levels of phosphate. The answer appears to be the increased use of phosphate additives in food.

Since the 1990s, our intake of phosphates in the form of food additives has doubled, from 500 mg a day to 1000 mg. The problem is that these food garde calcium phosphate are much more readily absorbed than the naturally occurring phosphates that are components of organic molecules, and therefore are more likely to lead to elevated phosphate levels in the blood.

Phosphate additives are widely used because they are very useful. Monocalcium phosphate, for example, is used in baking powder to generate carbon dioxide from sodium bicarbonate, meaning that many baked goods contain phosphates. Tricalcium phosphate is added to salt to keep it free flowing and disodium phosphate reduces cooking time of cereals. It is also used as an emulsifier in processed cheese, preventing butterfat from separating. Tetrasodium dihydrogen phosphate disperses solids in milk and is the secret behind thick milkshakes. Sodium acid pyrophosphate keeps potatoes from turning grey when boiled and phosphoric acid is added to cola beverages as a flavouring as well as to prevent the caramel colour from turning too dark.

An important property of phosphates is that they can sequester, or bind, metal ions like iron, copper and magnesium that are needed by bacteria for growth and also catalyze oxidation reactions. By binding these ions, phosphates act as preservatives. Canned seafood can form crystals of magnesium ammonium phosphate, known as struvite, that can look like tiny slivers of glass. Their formation can be prevented by phosphates that tie up the magnesium.

Perhaps the property that food producers favour the most is the ability of phosphates to bind water. Injecting ham, hotdogs, cold cuts or turkey with phosphates leads to a juicier product, but it also allows producers to sell water as if it were meat. These foods will declare phosphates on their labels, but in some cases they may be used without the consumer’s knowledge. “Purge” is the liquid that is released from raw meat as it ages. Consumers shy away from packages with high purge, resulting in reduced sales and increased waste. Treating the meat with phosphates reduces purge, resulting in increased sales.

Phosphates have also been accused of contributing to attention deficit hyperactivity disorder (ADHD) in children. This allegation is on much weaker footing than the claim that phosphates play a role in cardiovascular disease. There’s no real evidence here other than parents claiming that their hyperactive children improve on a low-phosphate diet. This may be due to the fact that a low-phosphate diet means eliminating processed foods, and it may be something else in these foods that is triggering the hyperactivity. In any case, there is no doubt that commercially processed food is much higher in phosphates than fresh food, and therefore a drive to reduce phosphates, a worthwhile effort, will lead to a cutback on processed foods, which is desirable for a variety of reasons.

If you would like a visual reminder of phosphate additives, next time you watch your bacon fry, note the shrinkage as the water that was bound by phosphates is released. The phosphates, though, stay behind, along with the salt and nitrites. Bacon is no health food. But you could have guessed that, since it tastes too good.

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