Could Diet Attack Bones?

Endocrinologist Deborah Sellmeyer of the University of California-San Francisco will publish some of the latest evidence early next year. She divided more than 9,000 women age 65 and older into five groups according to the overall acid load of their diet and found that women in the most acidic group suffered hip fractures 3.7 times more often than those in the least acidic group during the study’s seven year period.

It’s too early to be sure that a diet rich in meat and cheese is bad for your bones, say Robert Heaney, an endocrinologist at Creighton University in Omaha, although he calls it “an interesting and provocative hypothesis”. Clinicians including Uriel Barzel of the Albert Einstein College of Medicine in Bronx, NY already think that people worried about osteoporosis should replace some of their acid producing animal foods with fruits and vegetables. “Once you take estrogen out of the picture for women,” says Barzel, “I think second in importance is dietary acid”.

Looting the bones. Our kidneys ordinarily regulate the acidity of our blood by dumping excess acid in the urine, but the typical, protein rich American diet overloads them. Protein contains sulfur which our livers turn into sulfuric acid. The body has to neutralize some of it – by looting the bones. They’ve composed primarily of calcium phosphate and calcium carbonate, which are excellent bases for neutralizing acids. “An acidic environment actually stimulates cells called osteoclasts, which reabsorb bone mineral,” explains David Bushinsky, a nephrologist at the University of Rochester School of Medicine. Over many years, this process could weaken the bones.

Calcium rich foods can help the body make up for some of the loss, but a growing number of doctors think fruits and vegetables can also help because they produce acid-neutralizing bases. Anthony Sebastian of UCSF recently surveyed diet and hip fracture rates in 33 countries. He found “an absolutely phenomenal correlation” he says: “Differences in the ratio of plant to animal food accounted for 79% of the variation in fracture rates”.

Don’t just load up on rice and pasta though; grains actually generate a fair amount of acid. Instead, says Sebastian, focus on fruits and vegetables that are rich in potassium, such as bananas, apricots, and spinach. Potassium generally goes with base producing compounds, he explains. Oranges and tomatoes are fine; you may think of them as acidic, but they come out far on the basic side once metabolized.

And what about dairy foods, with their high calcium content? There, researchers are in a bind. While milk and yogurt are almost neutral, hard cheeses are among the most acid producing foods. “We advise increased dairy intake for women” says Sellmeyer. “The question isn’t, are we giving them extra calcium but potentially also giving them extra acid? I think it’s something we need to look into.

Vol 19 Issue 4 page 4