Don't think dairy when it comes to building strong bones, say proponents of the low-acid diet. Focus instead on a diet rich in fruits and vegetables, these nutrition scientists say.
The low-acid diet (also called the alkaline acid diet) has been the subject of scientific debate of late, as doctors and researchers question what, precisely, it takes to keep bones strong. The thinking behind the diet goes like this: Blood is slightly alkaline, with a pH just above 7. If the diet is rich in acids, the body tries to restore alkalinity by eliminating minerals, including potassium, magnesium and calcium, which the blood essentially pulls from the bones.
Following a low-acid diet doesn't mean avoiding vinegar and citrus fruits. On the contrary, it means not overloading on proteins, which are made up of amino acids that, as the name suggests, are acidic in nature. Low-acid diet adherents point out that because humans did not evolve on a diet heavy in meat and dairy, the modern Western diet, which is rich in animal proteins, may be contributing to illness and disease -- including osteoporosis.
That's the theory. What about the science?
"There's good evidence to suggest that pH in diet can make a difference" when it comes to bone health, says Dr. Bart Clarke, an endocrinologist specializing in osteoporosis and an associate professor of medicine at the Mayo Clinic in Rochester, Minn.
However, Clarke adds, the difference is small.
The theory was first proposed in the 1960s by scientists who hypothesized that human bones might be giving up calcium to compensate for pH imbalances caused by protein-rich Western diets. Evidence to support the theory accumulated in the 1980s, as scientists began to show that in rats, even small shifts in pH (such as a drop to pH 7.15 from 7.25) increased bone loss up to six-fold.
In test tube studies, acidity was shown to ramp up the activity of osteoclasts, cells that promote bone loss, and dampen that of osteoblasts, cells involved in bone formation.
Small studies in humans soon began to suggest that the body excreted more calcium, or less, depending on the acidity of the diet.
In a 1994 study by scientists at UC San Francisco that was published in the New England Journal of Medicine, calcium levels in urine decreased in 18 post-menopausal women who took potassium bicarbonate daily to neutralize the acid in their diets. The authors concluded that taking the potassium bicarbonate reduced the women's bone loss and increased bone formation.
