Chapter 76
Acid–Base Balance and the Bones
Influential organizations such as the U. S. National Osteoporosis Foundation and the Europe-based International Osteoporosis Foundation continue to advocate for dairy products, medications, and calcium supplements. Perhaps their objectivity is skewed by the influence of their commercial sponsors, which include companies that (you guessed it) sell dairy products, medications, and supplements. Concerns about conflicts of interest are justified here. Most recent reviews on dairy products and osteoporosis in the English-language medical literature come from authors with ties to the dairy industry. The primary justification for including dairy products in the US dietary guidelines is based on alleged benefits for bone health, which, however, are not supported by the available scientific evidence.
What would it look like if dietary recommendations were formulated independently of commercial influences? As already mentioned, Canada recently decided to stop including industry studies and to let the science guide the formulation of new dietary guidelines. There were profound changes, including putting plant-based eating at the center and removing the dairy group from the recommendations.
Acid–Base Balance and the Bones
For most of the last century, the prevailing theory in the field of nutrition was that consuming acid-forming foods such as meat carried the risk that you would pee your bones down the toilet. As I explain in my video see.nf/acidbone, however, we have since found out that most of the extra calcium excreted in the urine after a high-protein meal comes not from the bones, but from the additional calcium intake. So if our body is not primarily drawing on the bones to neutralize the acid from food, then how does it work? As I describe in Healthy Base, the answer may lie in our muscles. (The kidneys can balance the acids with a base they make from glutamine, a breakdown product of muscles).
Even so, bones can be attacked if the acid level in the body is high enough. Unfortunately, fractures occur as a side effect disproportionately often in children with severe epilepsy when they are fed a ketogenic diet. Just a few weeks may already harm bone remodeling values. Such diets cause persistent bone loss measurable in the spine, presumably because the ketones themselves are acidic and lead to a mild metabolic acidosis. It could also be due to all the saturated fat. In the Petri dish, the most commonly consumed saturated fat in the United States, palmitic acid, is toxic to bone-building cells. In general, there is a significant association between saturated fat intake and an increased risk of hip fracture.
As we get older, our blood pH shifts toward the lower (more acidic) end of the spectrum, perhaps because the kidneys can no longer excrete acid as well with age. In vitro studies suggest that this drop in pH could lead to activation of the cells that break down bone and blocking of bone-forming cells. This may help explain the following: When scientists removed base-forming foods (fruits and vegetables) from the diets of study participants, one of the markers of bone formation (bone-specific alkaline phosphatase) dropped significantly, while a marker of bone breakdown (CTX) shot up—and the reverse happened when participants ate six cups of fruits and vegetables per day.
In people over 65, the less balanced the ratio between acid- and base-forming foods, the greater the risk of a hip fracture. (Which foods belong to which group, please see the graphic elsewhere.) To determine cause and effect, randomized placebo-controlled double-blind trials lasting two years were conducted. Neither three nor the equivalent of six servings of fruits and vegetables had an effect; only potassium citrate, a base-forming compound equivalent to nine servings of fruits and vegetables per day, increased bone volume and density. With enough fruits and vegetables, it may be possible to offset the amount of acid in the typical Western diet and prevent bone loss.
Caring for the Skeleton—with Prunes
Inflammation and oxidative stress may also play a role in osteoporosis. Pro-inflammatory diets and increases in inflammation markers, such as C-reactive protein, are linked with osteoporotic fractures, and postmenopausal women with osteoporosis usually have more pronounced signs of oxidative damage and fewer antioxidants in the blood. Those are two more reasons why higher fruit and vegetable intake is associated with a lower fracture risk. And a third is vitamin C. Consumption of vitamin-C-rich foods is associated with a lower risk of bone loss, osteoporosis, and hip fracture. The risk of hip fracture falls by 5 percent per 50 milligrams of vitamin C consumed daily—that’s the amount in an orange. Which fruits/vegetables are especially good?
After feeding rats more than 50 different foods, researchers found that among fruits, prunes protected the bones best; among vegetables, it was onions. What about in humans? I discuss the available data at see.nf/prunes. It comes down to the fact that five or six prunes a day help maintain bone density.
But Onions Make Me Cry
And the onions? I discuss the preclinical and clinical data in see.nf/onionstomatoes. The bottom line is that onions can improve a bone loss marker in humans, but the study did not last long enough to see whether that leads to tangible benefits for bones. In a clinical study with other vegetables, that was at least the case.
It’s All Gravy
In the same video (see.nf/onionstomatoes), I discuss all the studies on tomato juice and sauce, as well as the Scarborough Fair diet (which includes prunes, onions, tomatoes, and supposedly bone-beneficial herbs such as parsley, sage, rosemary, and thyme, as in the song made famous by Simon & Garfunkel). The result is that we can stuff ourselves with whatever fruits and vegetables.
Tea and Abstinence
What about beverages? A meta-analysis on alcohol’s effect on osteoporosis found that people who had one or two drinks per day had a 34 percent higher risk of osteoporosis than abstainers. At more than two drinks a day, this risk rose to a whopping 63 percent, and that also means an increased fracture risk. This is partly due to alcohol’s negative effect on bone health and partly to impaired coordination, making it easier to fall.
Sugary sodas harm bones in a manner similar to salt: More calcium is excreted in the urine. It does not seem to be due to caffeine: More than three cups of coffee a day doubles hip fracture risk, whereas regular tea drinking significantly lowers it. When a randomized trial showed improved bone turnover values in women and rats had more bone mass after drinking tea, there was hope that it might be cause and effect. But the Minnesota Green Tea Trial, the largest and longest clinical trial of green tea extracts in postmenopausal women, found no significant benefit for bone density.
Nuts and Bones
Researchers in the world-famous lab of Dr. David Jenkins exposed human osteoclasts—bone-eating cells—to blood drawn from participants before and after they ate a handful of almonds. Details at see.nf/bonenuts, but overall the point is that almonds may support the prevention of bone loss but do not contribute to building bone, whereas with prunes it is the opposite—so trail mix made of prunes and almonds is probably best.