For today’s Dear Mark, I’m covering just one topic: the relevance of acid/base balance to health. Anyone wading through the morass of Internet diet information has come across the idea than an excess of acidity derived from our diet overloads the body’s ability to balance it with alkalinity. A diverse group invokes it, including strict paleo dieters, vegans grasping for straws to indict meat, and web sites featuring HTML from the 1990s that sell alkalizing water tablets. And because acidity sounds caustic and vaguely negative, lots of people buy into it. So, does it matter?
I often hear about the acid-alkaline properties of foods in the comments and forums. However, I am not sure if this has any scientific merit. You don’t seem to have any posts about it so would you care to shed some light on the matter?
Human blood likes to have a pH between 7.35 and 7.45, slightly above neutral. If pH dips too low and our blood becomes acidic, our cells stop working. This is called metabolic acidosis, and it comes in two flavors – acute and chronic. Left untreated, acute acidosis will kill you, while chronic acidosis leads to a host of health conditions that will eventually kill you or at least erode your quality of life:
- Muscle wasting
- Bone loss
- Glucose intolerance
- Growth hormone resistance (which can retard growth in kids)
When we metabolize foods and nutrients, some of them produce acids as byproducts. Acid-producing foods include meat, fish, grains, legumes, and dairy. They therefore represent a “high acid load,” and avoiding a high acid load is one of the main reasons many plant-based health types recommend avoiding animal foods. Our bodies, you’ve probably heard, just can’t handle the acidic fallout of all that meat and dairy without falling into metabolic acidosis.
Actually, the body has several ways to maintain the optimal pH range and avoid health problems in the face of acid-forming foods – and they’re extremely effective. If they weren’t, we’d be dead.
One way is through basic respiration – breathing. The lungs monitor the pH of our blood, prompting faster breathing when acidity needs to drop and slower, deeper breathing when acidity needs to rise. By exhaling carbon dioxide, we expel excess acidity. This is the primary way we compensate for fluctuations in pH.
Another way is through the kidneys. When acidity is high, the kidneys excrete more acids and produce bicarbonate, which returns to the blood as a buffering agent. Buffering agents combine with acids in the blood to neutralize them for easier excretion. There are other buffering agents, but bicarbonate is the primary one.
Yes, blood pH is tightly and most importantly unconsciously regulated. As long as your kidneys and lungs are working, the foods you eat will neither lower nor raise the acidity of your blood. What about those urine sticks that measure pH? Altering urinary pH with the food you eat is easy enough, but it doesn’t reflect blood pH. In fact, “acidifying” one’s urine by eating “too much” meat is proof that your kidneys are doing their job and excreting excess acid from the blood.
Thus we invalidate the most drastic claim about pH and health – that an acidic diet promotes acidic blood which promotes cancer. The body’s pH is maintained in a narrow range, regardless of the food you eat. Since its proponents are never able to cite any direct evidence beyond a misinterpreted Otto Warburg quote, I never put much stock in this claim.
But the next claim sounds more plausible: maintaining optimal pH in the face of acid-forming foods requires a calcium buffer that we leach directly from our bones. This leads to osteoporosis and the eventual dissolution of our entire skeletal system until we’re nothing but a disembodied urethra spewing brittle bone paste. Okay, that last part I made up. No one says that (I hope). There is evidence that appears to support the claim, which is why this idea has so much traction. First, consumption of the most acid-forming food of all, protein, does increase calcium excretion in the urine. And second, exposing in vitro bones to a metabolic acidosis test tube environment results in mineral dissolution, calcium loss, and production of the prostaglandins involved in osteoporosis.
Superficially, it’s compelling.
The entire premise falls apart when you look at the actual effects of consuming the most acid-forming food of all – protein – on the bones of real live humans. What happens to your bones when you eat protein? Although eating acid-forming protein often increases urinary calcium, it has an overall beneficial effect on bone metabolism and acid/base balance:
Dietary protein increases intestinal calcium absorption. Maybe it’s because the body “knows” it’s about to consume some bone-destroying acid-forming meat or whatever, but studies consistently show that eating protein also increases the amount of calcium we absorb. This is at least partially due to specific amino acids within the protein. At any rate, with more calcium available to the body, more will be excreted.
Dietary protein has no effect on bone resorption. Bone resorption is the removal of calcium from bone. If acid-forming protein were leaching calcium from your bones, resorption markers should be increasing. They don’t. Studies consistently show that eating protein has no effect on bone resorption.
Dietary protein increases renal function. People with existing renal insufficiency are often advised to lower their protein intake, but in healthy people with normal kidney function, eating sufficient protein is important for maintaining that function. By providing ammonia substrates, protein actually increases the kidney’s capacity to do its job and excrete acids.
The same goes for dairy, another acid-forming food that gets a ton of flack from many online health communities for its supposedly bone-dissolving effects. In truth, dairy is good for bone health. Maybe it’s the phosphate, which has been shown to reduce calcium excretion in the urine and improve calcium balance in the body. Or it could be the vitamin K2, a vital bone nutrient found in whole fat aged cheeses that improves bone mineral density in osteoporotic patients. Maybe it’s the dairy protein, which increases calcium retention and reduces bone calcium resorption while improving bone mineral density. Even when you add acid-forming dairy protein to a diet that’s already replete in acid-forming protein, it has no effect on bone mass or strength. There’s also the calcium to consider, along with the synergy of all the listed nutrients.
So it’s unsurprising that a diet high in meat and other acid-forming foods increases calcium absorption and excretion while lowering parathyroid hormone (a hormone usually elevated in osteoporosis).
If there is a problem with acid load, it’s only in people with renal insufficiency. Outright kidney failure can obviously cause metabolic acidosis, and it’s possible that gradually declining kidney function results in problematic low-level acidity. Kidney function certainly tends to decline with age, while the risk of fractures increases. Despite that weak connection between old age and renal insufficiency, seniors who eat more protein still have better bone calcium retention and absorption.
I’m not arguing that the acid/base balance of our blood isn’t important. It is. I’m arguing that the healthy among us are unable to consciously alter it, whether through the foods we eat or sheer will. And I’m arguing that some of the most acidic foods – meat and dairy – tend to have the most beneficial effects on bone health. Eating a purely acidic diet isn’t a good idea, but that’s because you’d be eliminating a ton of healthy plant matter with important nutrients, not because of the effect it has on your blood acid/base balance.
The weight of the evidence is clear: the acid-load of the diet has no effect on bone health in healthy people.
Thanks for reading, all.