The idea here is that lots of diseases -- cancer, heart disease, osteoporosis, and Alzheimer's are the four most commonly mentioned -- are caused by your body having an "acid pH." All you have to do, they say, is alter your diet to foods that result in "alkaline ash" (residues with a pH above 7) and you'll be healthy and happy and disease free. (Here's one example.)
As is the case with most of these sorts of claims, it has a kernel of truth. There are foods that result in alkaline ash; others that have acidic ash; and some that have neutral (pH = about 7) ash. The easiest way to monitor this is to test your urine pH, as your kidneys regulate your blood pH by excreting or retaining hydrogen ions, which is what pH is measuring in any case.
[image courtesy of the Wikimedia Commons]
But that's where the realistic bit ends, and the pseudoscience takes over.
The fact is, you can't change your body's pH, for the very good reason that it's one of the most tightly-regulated homeostatic factors in your body. Your blood pH is always 7.4. If it varies more than 0.1 pH points either direction, you are in a world of hurt. Here's a quick summary of what happens if your blood becomes more acidic:
pH = 7.4 -- happy and healthyAnd the same for moving in the alkaline direction:
pH = 7.3 -- blood acidosis; symptoms are shortness of breath, headache, confusion
pH = 7.2 -- dead
pH = 7.4 -- happy and healthySo the idea that by eliminating meat from your diet, you'll become more alkaline, and that's somehow healthy, is idiotic. Each tissue in your body has a particular pH at which it functions best -- some are acidic (e.g. the stomach), some are alkaline (e.g. the blood and the small intestine), and (more importantly) changing that pH in any of them would be a seriously bad idea.
pH = 7.5 -- blood alkalosis; symptoms are nausea, muscle spasms, twitching, numbness
pH = 7.6 -- dead
The bottom line is that if our pH yo-yoed around every time we ate a cheeseburger or an apple, we'd be dead. End of story.
Now, it's true that your urine pH varies a lot; that's because your kidneys are regulating your blood pH by excreting whatever it takes to keep your blood in homeostasis. So of course your urine pH changes. It's compensating for what you eat and drink. But there's nothing healthier about having alkaline urine. All it means is that your kidneys are working, which is the same thing that having acidic urine means.
The funny thing is, the "alkaline diet" site I linked above gives a nod to that idea in the following paragraph:
Even very tiny alterations in the pH level of various organisms can cause major problems. For example, due to environmental concerns, such as increasing CO2 deposition, the pH of the ocean has dropped from 8.2 to 8.1 and various life forms living in the ocean have greatly suffered. The pH level is also crucial for growing plants, and therefore it greatly affects the mineral content of the foods we eat. Minerals in the ocean, soil and human body are used as buffers to maintain optimal pH levels, so when acidity rises, minerals fall.Right. So that's why we have kidneys. So that kind of shift in pH and other electrolytes doesn't kill us.
You'd think that a quick perusal of sites regarding actual research on the effects of diet (here's a good example) would immediately settle that point, but unfortunately the availability of correct information hasn't stopped the claims. And worse, there are people now selling all sorts of supplements that are supposed to regulate our pH, and without which dire things are predicted to happen.
Me, I'm fond of the dietary advice "everything in moderation." Listen to your body, make your decisions based on actual research, don't spend your money on useless supplements, and don't go crazy overboard on something like the amazing grapefruit-and-peanut-butter diet. (I don't know if that actually exists, but given some of the bizarre diets out there, I'll bet it does.)
Best of all, learn a little bit of biology. It's cool, it's interesting, and it'll keep you from getting suckered by alt-med nonsense. And with that, I think I'm going to go have some bacon and eggs for breakfast, confident in the knowledge that my kidneys are up to the challenge.