Nutrition Action Healthletter spoke on the phone with Bess Dawson-Hughes, the director of the Bone Metabolism Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University and a professor of medicine at Tufts. This is what she had to say about acid and bone health.
Q: What’s the deal with acid and bone health?
A: We have growing evidence that foods that create acids in the body lead to bone breakdown. Bone is an alkali reservoir, so when you break bone down, you’re putting alkali into the circulation to neutralize the acid. The bone acts as a buffer.
Researchers have even found a signal that tells the bone to break down when the environment becomes acidic. It’s how our bodies adapt to increasing acid.
Q: Does acid come from acidic foods?
A: No. The acid comes from foods that get broken down into compounds that produce hydrogen ions, which is what makes something acidic. Those foods are cereal grains and protein.
Q: Both plant and animal protein?
A: Yes. The acid story doesn’t hinge on whether the protein is plant or animal.
In contrast, eating fruits and vegetables provides alkali to the system, which is good. Orange juice is clearly acidic, but when it’s absorbed into the body, it gets broken down into bicarbonate, which is alkali.
Q: Do we have evidence that fruits and vegetables prevent fractures?
A: Not yet, but the evidence is getting stronger. For example, one study gave 52 healthy men and women either a placebo or a moderate or high dose of potassium citrate for six months. Like fruits and vegetables, potassium citrate gets metabolized to alkali in the body.
People who got the placebo lost more calcium than they consumed. People who got the lower dose of potassium citrate retained more than they consumed, and those who got the higher dose retained even more.
Q: Did that make their bones denser?
A: That study didn’t look, but another study gave 201 healthy men and women age 65 and older a moderate dose of potassium citrate for two years. They saw significant improvement in bone mineral density at the spine, hip, and total body. And they saw a decrease in bone turnover. So these two studies go pretty far in supporting a role for alkali in protecting bone.
We have a big trial funded by the National Institutes of Health that will end in December. So, a few months after that we will know whether potassium bicarbonate, another alkali, had any effect on bone turnover or on muscle.
Q: So alkali can also affect muscle?
A: Yes. In our last trial, the alkali group had greater muscle power in their legs and a drop in nitrogen excretion. That strongly suggests decreased muscle loss.
The hypothesis is that in the acid environment, muscle wasting helps the body get rid of acid. For every amino acid it loses, the body dumps a hydrogen ion into the urine. So muscle breakdown neutralizes acid by taking hydrogen out of the system. It’s fascinating.
Q: Does protein cause calcium loss?
A: People used to think so, because protein increases calcium excretion in the urine. But protein also increases calcium absorp¬tion in the gut, so there’s no net loss.
However, to lower your acid load, you could drop your protein and/or your cereal grains intake. By that I’m talking about bread, rice, cereal, and other grains, all of it—even whole grains.
Q: And bagels, buns, burritos, pizza, pasta, lo mein, rice, muffins, doughnuts, cakes, and cookies?
A: Yes. Given our concerns about obesity, cutting back on cereal grains is a good way to balance your acid-base status.
Q: Because cutting protein may not be good for older people?
A: Yes. A number of people in the muscle field think that the RDA for protein isn’t quite high enough for older people.
Now, there are exceptions. For example, people on protein-loading diets like the Atkins diet or bodybuilders who take excessive amounts of protein should get less.
Also, when people get older, they have a decline in renal function. That fuels this acid-base problem because the older kidney is not as efficient at removing hydrogen ions. That’s why the acid issue is more of a problem for elders.
People whose renal function has declined substantially are advised to reduce their protein intake. That’s a big group of people.
Other relevant links:
• How much calcium should you be consuming to protect your bones? See: Dietary Supplements: Calcium and Bone Health
• Learn how vitamin D and calcium work together towards bone health. See: Dietary Supplements: Can Vitamin D Protect Bones?
• What kind of exercises strengthen your bones? See: Exercise for Health: Does Exercise Help Bones?