Subtle Larceny: Too Little Protein in
Dietitian Jackie Charnley discusses the protein needs study
with volunteer Faith MacDonald at the Jean Mayer USDA Human Nutrition Research
Center on Aging at Tufts University in Boston, Massachusetts.
Most Americans get more than enough protein in their diets.
And there's evidence that too much protein puts a strain on the kidneys
because our bodies excrete the excess rather than store it as we do fat or
But about 10 percent of European American women and 20 percent of African
American women over age 55 consume less than 30 grams of protein daily, even
though they get ample calories, according to the second National Health and
Nutrition Examination Survey. That's half the Recommended Dietary Allowance
"We're concerned about that group," says Marilyn C. Crim, a
physician and nutrition scientist at the Jean Mayer USDA Human Nutrition
Research Center on Aging at Tufts University in Boston.
"Elderly women who consume well below the RDA may be adapting by losing
lean body mass and muscle function. This increases their risk for
Dietary protein provides the raw material for muscle, bone, and internal
organs, as well as for the enzymes that make our metabolic processes go.
Says Crim, "If we can prevent loss of muscle functionthe ability
to get around and perform normal tasksthen I feel we can help them."
The issue has even broader international implications.
"In Guatemala and other developing countries, people get about
three-quarters of the RDA on average. Many get only half the RDA," says
Carmen Castaneda, a physician from Guatemala and now a nutrition scientist at
the USDA center.
Her interest in the effects of low-protein diets led her to design a 9-week
study with Crim and others for her doctoral thesis. Throughout the study, six
women were given meals plus a beverage with enough milk proteins added to bring
their protein intake a little above the RDA. Another six got the same meals and
a low-protein beverage, providing about half the RDA for protein. The women
were between 66 and 79 years old.
Few studies have assessed the amount of protein required by people over age
50. Until there's more data, the National Research Council has kept the RDA for
elders the same as for adults under age 50 0.8 gram per kilogram of body
weight per day. For a 140-pound person, that translates to 63 grams of protein
each day. That's about the amount in two chicken breasts, three ground beef
patties, or a cup of tuna salad.
Volunteer Faith MacDonald performs arm-strength testing under
the supervision of physicians Marilyn Crim (center) and Carmen Castaneda, who
are also nutrition scientists.
Traditionally, protein requirements have been based on the amount people
needed to stay in balance. That's when protein intake matches the amount being
excreted from the body. When protein intake drops, people will excrete more
than they eat for a while, explains Castaneda. Eventually, they reach a
balance. "But you don't know what changes the body went through to reach
that balance," she says.
Crim emphasizes that biochemical measurements "don't tell you much
about how well the person functions in everyday life. We're in a new era of
looking at physiological function as part of the parameters we measure."
To study the impact of adapting to low-protein intakes, the researchers
measured the women's muscle function, their body composition, and their immune
responsein addition to blood protein levels and nitrogen balanceto
detect any changes.
Proteins are unique among the major nutrients in that they contain nitrogen.
Researchers can follow protein intake and excretion rates by measuring
Only one of the women given half the protein RDA reached nitrogen balance by
the end of 9 weeks, says Castaneda. The rest were almost in balance but still
excreting more than they consumed. And the body's attempt to reach equilibrium
took its toll on all of them.
"These women had significant losses in lean tissue, immune response,
and muscle function," says Castaneda.
They lost an average 8 percent of lean tissue, most of which was muscle. One
measure of immune responsea hypersensitivity skin testwas 50
percent lower by the end of the study. And the amount of weight they could push
in a chest press exercise dropped by 12 percent.
By contrast, the six women who consumed a little more than the RDA stayed in
nitrogen balance throughout the study without any changes in muscle mass. In
fact, several measurements of muscle function and ermine response improved
significantly, as did several blood protein measurements.
"Our findings suggest that this 'healthy' group of women may not have
had an optimal diet prior to the study," the researchers conclude.
They also speculate that "the loss of lean tissue that has been
attributed to aging may be due, in part, to chronic dietary protein
"The women did very well on the higher protein dietwhich averaged
15 percent more than the current RDA," says Castaneda, noting that the
study was not designed to determine a protein requirement.
The most striking impairment in the low-protein group may turn out to have
an important implication. It occurred in a muscle function test that measures
how long it takes the thumb's adductor pollicis muscle to contract and relax
after a mild electrical stimulation.
This test has been used as a measure of early stages of starvation, says
Castaneda. "We're looking for early indicators of chronic protein
malnutritionwhen people are getting ample calories."
Just 3 weeks into the studybefore any measurable changes in body
composition had occurred, the women on the low-protein diet had a 46-percent
drop in normal muscle response to this test. By Judy McBride,
Mayer USDA Human Nutrition Research Center on Aging at Tufts University,
711 Washington St., Boston, MA 02111; phone (617) 556-3000; fax (617) 556-3344.
"Subtle Larceny: Too Little Protein in Elders"
was published in the July 1995 issue of
Agricultural Research magazine.