XIENCE ME% of the week

Do Meat and Dairv H a m Aging Bones? With advancing age, our bodies expe-

rience an inexorable loss of bone. Two major studies in elderly populations now underscore the importance of dietary pro- tein in this structural erosion, which can lead to osteoporosis. The reports come to sharply different conclusions, however, about the effect of animal protein on the rate of bone loss.

In one study, diets rich in animal pro- tein correlated with greater bone loss and fracture risk. In the other, animal pro- tein appeared to protect bone.

Such contradictions, “which are not very satisfying,” often emerge from obser- vational studies where researchers record the natural habits and health of people, notes Robert P. Heaney of Creighton Uni- versity Medical Center in Omaha, Neb. “That’s not a criticism of such studies,” he says, just a reminder of the uncontrollable variables rife in populations.

However, he notes, the new studies are important because they’re in the van- guard of efforts to understand protein’s impact on agerelated bone loss. This con- dition underlies a growing U.S. epidemic of hip fractures. Treating them costs more than $10 billion annually.

The first of the new analyses comput- ed bone loss over 7 years in some 750 elderly women, all taking part in a larger osteoporosis study that’s been running since 1986 at four U S . sites.

Women eating the most animal pro- tein-roughly four times their vegetable- protein intake-lost 0.8 percent of the bone in their hips annually, notes en- docrinologist Deborah E. Sellmeyer, direc- tor of the University of California, San FrancisceMount Zion Osteoporosis Cen- ter. This is four times the rate of bone loss in participants who ate about equal parts animal and vegetable protein.

The risk of hip fractures in women eat- ing the highest proportion of animal pro- tein was 3.7 times that in women regular- ly downing equal quantities of animal and vegetable protein, the team reports in the January AMERICAN JOURNAL OF CLINI- CAL NUTRITION.

The findings make sense, Sellmeyer ar- gues, because digestion of animal protein unleashes large amounts of acid that the kidneys must excrete. Previous studies showed that when kidney function wanes with age and calcium intake drops, the body draws upon skeletal calcium to buffer the resulting buildup of acid, thus eroding bone. Most of the women in this study consumed only about half of the 1,500 milligrams of daily calcium recom- mended for people their age.

In a younger person whose kidney function is robust and calcium intake

20

J high, diets rich in animal products can help build bone, Sellmeyer notes.

In the recent study, the women eating the least animal protein also averaged only 70 percent as much total protein as did those eating the most animal protein.

Data from 600 senior citizens in the long-running Framingham (Mass.) Osteo- porosis Study paint a picture quite differ- ent from Sellmeyer’s results. Over a 4-year period, Marian T. Hannan of Harvard Medical School in Boston and her team measured changes in bone density among the elderly men and women.

Participants eating relatively little pro- tein-from any source-lost about 1 per- cent of their hip and spine bone annually, whereas people eating the most protein held bone losses to about one-quarter of that. The scientists report their findings in the December 2000 JOURNAL OF BONE AND MINERAL RESEARCH.

J

Soon, plywood might go vegetarian. The ubiquitous building material owes

its strength to multiple wood sheets with their grains at right angles and tena- cious glue between the layers. Now, re- searchers are proposing that plywood be manufactured using glue made with soy flour rather than with powdered cattle- blood protein, as is done conventionally. The vegetablecontaining adhesive might reduce the wood’s cost and alleviate health concerns among mill workers.

A leading incentive for finding such an alternative is workers’ fears of breathing in cattle-blood dust and disease agents it might carry, says Mila P. Hojilla-Evan- gelista of the U.S. Department of Agri- culture’s Agricultural Research Service (ARS) in Peoria, 111. Furthermore, there are few suppliers of the blood protein, which helps make the glue sticky and durable.

In work funded by the United Soybean Board, Hojilla-Evangelista and her col- leagues developed and tested several glue formulations that use different amounts of soy ingredients from a variety of suppli- ers. Three glues that contain soy flour-a combination of soy protein and starch- have properties comparable to those made with the blood protein, says Hojilla- Evangelista. In tests, the soycontaining glues were at least as strong as the con- ventional glue and had comparable water resistance, she says.

The new glues also had foaming be- havior comparable to that of blood-prcF tein glue. Foaming is an essential trait for glue used in one of the major meth-

In this study, the ratio of animal to veg- etable protein was high and differed little among participants. Still, animal protein didn’t seem deleterious. In several sites especially vulnerable in osteoporosis, seniors routinely downing the most ani- mal protein showed bone loss at only about half the rate of those eating the least animal protein.

Two years ago, Ronald G. Munger of Utah State University in Logan and his colleagues reported similar evidence for a protective effect of animal protein in their study of hip fractures in Iowa women. But Hannan and Munger both say that am- ple consumption of meat and dairy prod- ucts might also be a marker for a well- rounded diet that’s good for bones.

One unambiguous take-home message from all these studies, Sellmeyer says, is that elderly people “need to maintain a good protein intake.” -J. Raloff

Sovbeans could beef up plywood glues ods for making plywood. During this manufacturing process, known as foam extrusion, machines squirt the glue in evenly spaced lines onto each succes- sive ply, says Rick Haig of ARS.

Good foaming ensures that the glue will coat the entire sheet when another layer of wood is pressed on. Foam extrusion us- es less glue than other techniques, such as brushing, rolling, or spraying, he says.

Pacific Adhesives Co. of Portland, Ore., which makes foamextrusion equipment, is now testing the ARS formulations. In these experiments, the soycontaining glues foam just as well o r better than bloodcontaining glue, says company president Tom Demaree. The company is still examining the soy glues’ adhesive properties, he says, and is planning full- scale mill trials.

Paper and wood materials giant Geor- gia-Pacific is also testing several formu- lations of the new glue, says company researcher Me1 Foucht in Decatur, Ca. “I think that it has a lot of potential,“ he comments. For one thing, he says, the soycontaining glue has a longer shelf life than conventional glue. He specu- lates that the soy glue might not be limit- ed to foamextrusion processes.

Ultimately, cost may determine the new glues’ fate. The soy glues are slight- ly less expensive than those that con- tain animal protein, Hojilla-Evangelista says. Although modest, such savings could add up for mills that use tons of glue annually to make industrial quanti- ties of plywood. -4 Corman

SCIENCE NEWS, VOL. 159 JANUARY 13,2001