Getting Your Protein From Plants, Instead of Animals, May Protect Bone

EatBeans2High protein diets increase the risk for bone fracture. That doesn’t mean protein isn’t important.  Too little protein also increases the risk for fracture.  I’ve seen some vegetarian diets that left their consumers dangerously low in protein. I mean, if all you’re going to eat is bananas…

How do you protect your bones if you’re cutting back on animal foods? Get your protein from plants:

A High Ratio Of Dietary Animal To Vegetable Protein Increases The Rate Of Bone Loss And The Risk Of Fracture In Postmenopausal Women, American Journal of Clinical Nutrition, 2001

“Elderly women with a high dietary ratio of animal to vegetable protein intake have more rapid femoral neck bone loss and a greater risk of hip fracture than do those with a low ratio. … These associations were unaffected by adjustment for age, weight, estrogen use, tobacco use, exercise, total calcium intake, and total protein intake. … This suggests that an increase in vegetable protein intake and a decrease in animal protein intake may decrease bone loss and the risk of hip fracture.”

BoneLossFemoral2

HipFracture2

What’s the mechanism?

“Different sources of dietary protein may have different effects on bone metabolism. Animal foods provide predominantly acid precursors, whereas protein in vegetable foods is accompanied by base precursors not found in animal foods. Imbalance between dietary acid and base precursors leads to a chronic net dietary acid load that may have adverse consequences on bone.”

It isn’t just bone that weakens when exposed to a high animal protein diet, it’s muscle too:

“… skeletal muscle, like bone, may serve as a reservoir of base that is gradually depleted to maintain acid-base balance. … Muscle mass decreases during experimentally induced metabolic acidosis. … Chronic depletion of skeletal muscle could lead to weakness and a greater number of falls, both factors in hip fracture.”

Note that those who had the highest ratio, who ate the most animal food, also had the highest calcium intake (1124 mg/day vs. 662 mg/day). Those eating a high animal food diet took in over 2/3rds more calcium and still had more bone loss and fractures.

What plant foods are good sources of protein? See my logo.

4 thoughts on “Getting Your Protein From Plants, Instead of Animals, May Protect Bone

  1. Bix Post author

    I should elaborate on my last sentence. Thank you, Marj! Beans and lentils are a good source of plant protein, but there are lots of other foods … nuts and seeds, some grains like quinoa. You can go to NutritionData, http://nutritiondata.self.com/ to tailor a diet. Click on “Tools” then “Nutrient Search Tool” There’s a drop-down menu that allows you to find foods that are high in something, say protein, and then pick a food category. It’s a little cumbersome because it returns a lot of foods but you can skim it for ideas or try another food group. I love playing with it.

    The only thing … watch the serving size. I just plugged in protein and it said chives were a good source, 21 grams protein, but that’s for 100 grams of chives! or about 1/4 pound. To this day I still make that mistake.

    Another point … There are differences in animal and vegetable protein, besides acid load. Vegetable protein has different amounts of some amino acids (like the sulfur-containing amino acids) and may be more difficult to digest and absorb. But you can still get all the protein and all the amino acids you need on a vegan diet, and the benefits (like lower fracture rates) may outweigh the costs.

    Reply
  2. Bix Post author

    There’s something a bit weird about what I’m reading… I’m finding that bone mass density (BMD) is not strongly associated with fracture. In fact, in some cases, the denser the bones, the higher the fracture rate:

    “The long-term consequence of this reliance on bone to buffer the endogenous acid would be increased rates of skeletal loss and a decrease in bone mineral density (BMD). However, the epidemiological data bearing on this point support a different conclusion. There are at least 10 epidemiological studies in which BMD is the primary outcome showing that a high protein diet is associated with a high BMD (not a low BMD, as might be predicted) (39–48). There is only one study showing a negative association (49) and four showing no association (50–53). The nutrition intervention studies in which markers of bone turnover were measured under various protein conditions are few and inconsistent (23,54).

    “The hypothesis would also predict that a long-term, high protein diet would increase fractures. Surprisingly, given the BMD data, the epidemiological evidence, by and large, demonstrate an increased fracture rate in populations consuming high protein diets (55–58) with only one divergent study (59). The discrepancy between the BMD and the fracture epidemiological data is not understood, at this point.”

    So, a high protein diet can increase bone mineral density, but at the same time increase fractures. I wonder what this says about those bone density DXA scans.

    Reply

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