The Standard American Diet is very acid-producing. I wrote about acidic vs alkaline diets here

This does not mean your food actually causes acidemia, or a drop in blood pH, because your blood buffering system keeps your blood pH around 7.35 (and ideally closer to 7.40). Buffers keep your blood pH from changing too much, even when a very high or very low pH substance gets introduced to it. It’s like a shock absorber.

But acid-forming foods do tax your blood buffering system, leading to certain predictable consequences. Among them are osteoporosis and kidney stones. Incidentally there is also evidence that acidosis may increase the risk of diabetes and encourage cancer cell growth as well. 

Quick chemistry interlude:

An acid is any chemical substance that releases a proton ion (H+). A base is any chemical substance that accepts a proton ion. 

Adding more protons to your bloodstream will decrease its pH, so your body has a fancy buffering system to balance them out. The system involves:

  • Bicarbonate (HCO3-), which is stored in your bones and bound to either calcium or sodium (Ca+ and Na+), and
  • Phosphate (PO4-), which is also stored in your bones, complexed with calcium.

Why acidity leads to bone loss

When your bloodstream has excess protons (acid), your body pulls some of these basic ions, such as bicarbonate and phosphate, from your bones in order to maintain a pH of 7.35-7.40. But this means your bones lose calcium, because phosphate and bicarbonate are bound to calcium. This is why overtaxing the buffering system can lead to osteoporosis

What foods cause this to happen?

Most foods do not directly dump protons into your bloodstream. Whether they are classified as acidic or basic depends on how they are metabolized.

  • Base-producing foods: Foods high in potassium (i.e. plants) form bicarbonate (a base) when metabolized.
  • Acid-producing foods: Proteins (i.e. meat) high in the sulfur-containing amino acids methionine and cysteine become sulfuric acid.
  • But the biggest culprit is sodium. Sodium is responsible for the vast majority of the acidosis-producing effect of the diet. Foods that contain lots of sodium: pretty much any processed grain product (including yeast containing bread, pizza, pasta, grain-based desserts, and tortillas), processed meat products (including sausage, hot dogs, cold cuts, and bacon), and other pre-packaged processed foods (regular “American” cheese, soups, boxed meals, condiments, etc).

Your kidneys: The buck stops here

Ultimately your kidneys are responsible for getting rid of excess protons and reabsorbing bicarbonate to restore the balance in the blood. In order to do this, they must spill many other ions into the urine, including calcium, and decrease elimination of the negative ion citrate, which helps dissolve calcium. Most kidney stones (75-85%) are made of either calcium oxalate or calcium phosphate. What this means is, there’s a direct correlation between the acidic Standard American Diet and the formation of the most common kind of kidney stones

(And by the way, the reason soda is correlated with kidney stones is because soda is high in phosphate, which is the other half of calcium phosphate and magnesium ammonium phosphate stones.) 

What you can do: 

  • Limit your sodium intake. Go ahead and add sea salt to your food to taste, but avoid the sodium found in prepackaged foods. In fact, avoid prepackaged foods whenever possible.
  • Increase your potassium intake. In other words, eat your fruits and veggies. Lots of ‘em.
  • Don’t overemphasize meat. This is one reason why super low carb diets can be problematic: while I’m not at all against organic and free range meat and encourage its consumption in moderation, an Atkins-style diet can cause kidney problems because of the high acid load coming from those sulfur-containing amino acids.
  • Drink plenty of water. As long as we’re talking about the kidneys, this is one of the very best things you can do to keep them healthy. Drink half your body weight in ounces daily.

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