Onions and Tomatoes Put to the Test for Osteoporosis

Feeding rats dozens of different foods, the fruit found to preserve their bones the best was the prune, and the leading vegetable was the onion. I’ve talked already about prunes. What about onions?

The country with apparently the highest per capita consumption of onions in the world is Turkey, which also has one of the lowest rates of osteoporotic bone fractures. Turkey may have four times greater daily per capita onion intake than the United States and four times lower hip fracture probabilities. Is that just a coincidence though?

The problem with trying to correlate country-by-country comparisons is that you don’t know if the people within those countries who are actually eating those onions are the ones who are actually avoiding fractures. But in 2017, a prospective study was published in which the fruit and vegetable intake of about 1,500 older women was followed for nearly 15 years, and of all of the classes of vegetables, the intake of allium family veggies (such as onions, leeks, and garlic) were the ones most associated with lower risk of bone fractures.

Based on a study of non-Hispanic white women 50 years and older, those who ate onions on a daily basis had an overall bone density 5 percent greater than those who rarely ate them. That may not sound like a lot but could potentially translate into reducing the risk of hip fracture by more than 20 percent.

Why onions? Maybe it’s the quercetin. Onions are one of the most concentrated sources of this phytonutrient, which can stimulate the activity of our bone-building cells, at least in a petri dish, and is also a potent inhibitor of the formation of new bone-eating cells.

Or, could it be the fructan-fiber-prebiotics in onions? Experimentally infused into the rectum, the short-chain fatty acids created by our fiber-eating gut flora have been shown to stimulate calcium absorption, so much so that adolescents randomized to the type of fiber found in onions—about an onion a day’s worth for a year, significantly increased their bone mineral density over the placebo group.

In the rodent bone preservation study, a number of spices beat out prunes and onions, with the top dog being another allium, garlic. And, in the prospective human study, cruciferous vegetables like broccoli came in at a close second to the allium family. Although there are some petri dish data supporting the potential bone benefits of the sulforaphane in cruciferous veggies, inhibiting the formation of bone-eating cells, and it appears to protect bone health in mice, the reason I’m singling out onions is that it’s one of only two vegetables that have actually been put to the test in clinical trials.

But, how are you going to come up with a placebo onion for the control group? That’s why a group of innovative Chinese researchers gave people onion juice versus a fake onion juice. (I don’t know which sounds worse, but anything for science!) And, those randomized to the real onion group experienced an improvement in a marker of bone loss over the placebo, but the study didn’t last long enough to see if this translated into tangible bone benefits. But, a clinical trial on the other vegetable put to the test, did.

The tomato story, starts out, like the onion story. There’s epidemiological support. In the Framingham Osteoporosis Study, higher intakes of lycopene, the red pigment in tomatoes, were associated with protection against bone loss in older men and women over a period of four years, as well as protection against hip fractures over seventeen years. Perhaps this helps explain why studies show that increased adherence to a more Mediterranean-style diet is associated with about 20 percent fewer hip fractures.

Then, there’s laboratory evidence. Lycopene inhibits bone loss in a petri dish and preserves bone mass in rats. However, so does green tomato extract, which is richer in compounds such as tomatine rather than lycopene; so, maybe there are multiple protective factors in tomatoes. Anyway, let’s feed people some tomato products and see what happens!

Postmenopausal women randomized to lycopene in the form of about a cup and a third of regular tomato juice a day experienced a significant reduction in a marker of bone loss by month two, and the opposite was found after just a month of restricting lycopene consumption (so, no tomatoes, watermelon, or other red fruits like pink grapefruit). This suggests that just regular dietary intakes are protective. But does this translate into retaining significantly more bone over time? Postmenopausal women given about two-thirds of a cup of tomato sauce a day for three months suffered significantly less bone loss than those in an age-matched group who didn’t, though it does not appear that the study subjects were assigned randomly, which could bias the results.

So, should we go out of our way to include these specific fruits and vegetables in our diet? Normally, we’re just left with a “can’t-hurt” shrug, but a group of New Zealand researchers put together a randomized controlled trial to find out. They developed the Scarborough Fair Diet (named for the presence of presumptive bone-protecting herbs parsley, sage, rosemary, and thyme from the song popularized by Simon and Garfunkel). The diet included prunes, onions, and tomatoes. They compared that to a diet similarly packed with nine or more servings of fruits and vegetables, but ones that were not suspected as having particularly skeleton-saving properties. Markers of bone turnover were measured after three months, and the specially concocted diet of bone-preserving produce did no significantly better than the diet packed with non-bone preserving produce, or a diet with just six servings of fruits and veggies a day, suggesting that the focus should just be on stuffing your face with fruits and vegetables of any stripe.