The Paleo Diet - Loren Cordain [13]
But what about calcium? Surely, eating a lot of cheese can help prevent osteoporosis? The answer is a bit more complicated. One of the great ironies of the low-carbohydrate, high-fat diets is that even though they allow unlimited consumption of high-calcium cheeses, they almost certainly will be found to promote bone loss and osteoporosis in the long run. How can this be? Because getting a lot of dietary calcium from cheese, by itself, isn’t enough to offset the lack of fruits and vegetables.
Nutrition scientists use the term “calcium balance” to describe this process. It’s the difference between how much calcium you take in and how much you excrete. Most of us have gotten the message about consuming calcium. But the other part of the equation—how much calcium you excrete—is just as important. It is quite possible for you to be in calcium balance on a low calcium intake if your calcium excretion is also low. On the other hand, it’s easy for you to fall out of calcium balance—even if you load up on cheese at every meal—if you lose more calcium than you take in.
The main factor that determines calcium loss is yet another kind of balance—the acid-base balance. If your diet has high levels of acid, you’ll lose more calcium in your urine; if you eat more alkaline foods, you’ll retain more calcium. A study in the New England Journal of Medicine by my colleague Dr. Anthony Sebastian and his research group at the University of California at San Francisco showed that simply taking potassium bicarbonate (an alkaline base) neutralized the body’s internal acid production, reduced urinary calcium losses, and increased the rate of bone formation. In a follow-up report in the New England Journal of Medicine, Dr. Lawrence Appel at Johns Hopkins University reported that diets rich in fruits and vegetables (these are alkaline foods) significantly reduced urinary calcium loss in 459 men and women.
See Appendix A for a list of common foods and their acid-base values.
Cereals, most dairy products, legumes, meat, fish, salty processed foods, and eggs produce net acid loads in the body. By far the worst offenders on this list are the hard cheeses, which are rich sources of calcium. Again, unless you get enough fruits and vegetables, eating these acid-rich foods will actually promote bone loss and osteoporosis.
Virtually all fruits and vegetables produce alkaline loads in the body. When you adopt the Paleo Diet, you won’t have to worry about excessive dietary acid causing bone loss—because you’ll be getting 35 percent or more of your daily calories as healthful alkaline fruits and vegetables that will neutralize the dietary acid you get when you eat meat and seafood.
Toxic Salt
Most low-carbohydrate, high-fat diets don’t address the dangers of salt; some even encourage its use. And yet there is a ton of medical evidence linking salt to high blood pressure, stroke, osteoporosis, kidney stones, asthma, and even certain forms of cancer. Salt is also implicated as a factor in insomnia, air and motion sickness, Ménière’s syndrome (an agonizing ear ringing), and the preeclampsia of pregnancy.
Salt is made up of sodium and chloride. Although most people think that the sodium portion of salt is entirely responsible for most of its unhealthful effects, chloride is just as guilty, if not more so. The average American eats about 10 grams of salt a day (this turns out to be about 4 grams of sodium and 6 grams of chloride). Chloride, like cereals, dairy products, legumes, and meats, yields a net acid load to the kidneys