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Protein: a bone of contention
10/31/2005
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New findings may weaken the weak consenus concerning protein and bones
by Craig Weatherby 


You’ll likely run across this list of "lesses" in many essays about bones and nutrition: Asians and other societies less meat-focused than ours suffer less osteoporosis because they eat less protein.

Health authorities often caution people against eating too much protein, lest they suffer weakened bones. Why would this happen?  Digestion of protein releases acids that the body neutralizes with alkaline chemicals, some of which can be calcium pulled from its bones.

This view has some evidence, albeit slight, to back it up. Some large health surveys suggest a connection. And, among the many thousands of women who’ve participated in the famed Nurses' Health Study, those who averaged more than 95 grams (3.4 ounces) of protein a day were 20 percent more likely to break a wrist over a 12-year period, compared with those whose daily intake approximated the group average of less than 68 grams (2.4 ounces) per day.

However, skeptics note that athletes who eat considerably higher amounts of protein than average seem not to suffer bone weakness.  On the other hand, most engage in some resistance exercise (weight training, pushups, etc.), which is proven to build bone size and strength.

United States government guidelines recommend that women over 25 consume about 50 grams (1.8 ounces) of protein per day, which is just a bit more than the 46 grams of protein you’d get from one of our six-ounce sockeye salmon fillets

(To view a chart by the Harvard School of Public Health showing the amounts of protein in other foods, click here.)

Aussie study delineates dangers of low-protein diets
According to the results of a study out of Australia, there may be more to the protein picture than conventional wisdom contemplates.

In a study published last June, researchers at the University of Western Australia found that older women who consume more dietary protein enjoy increased bone mineral density (BMD): a common measure of the vulnerability of bones to fracture.

They followed 1,077 women aged 72 to 78 over the course of a year, to see what effect different amounts of dietary protein would have on bone density. The results showed that higher protein intake was associated with better bone density, after adjusting for age, body mass index and the effect of other nutrients.

Women who ate less than 66 grams (2.3 ounces) of protein per day had significantly lower bone density in the heel and hip than did women who ate more than 87 grams (3.1 ounces) of protein per day.

The scientists concluded that women need to consume more protein than the 50 grams (1.8 ounces) current guidelines suggest.\n\nGiven the possible negative effects of eating too much protein, and the demonstrated downside of eating too little, it makes sense to aim for that sweet spot in the middle.

The available data indicate that to protect bone health, women should ingest about three ounces (84 grams) of protein per day. It's not such a hard target to meet, when you spread the protein intake across various good food sources, such as fish, dairy, meat, nuts, and combinations of grains and beans.

And it only makes sense to favor fish for protein, as it is among the healthiest sources. To give you a sense of what three ounces of protein per day means in terms of fish, it's a bit less protein than you'd get (3.3 ounces or 93.6 grams) from two cooked, six-ounce sockeye salmon fillets.


Sources
  • Devine A, Dick IM, Islam AF, Dhaliwal SS, Prince RL. Protein consumption is an important predictor of lower limb bone mass in elderly women. Am J Clin Nutr. 2005 Jun;81(6):1423-8.
  • Harvard School of Public Health Nutrition Source. Protein: Moving Closer to Center Stage. Accessed online October 22, 20056 at http://www.hsph.harvard.edu/nutritionsource/protein.html

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