In two studies, researchers doubled the protein RDA (Recommended Dietary Allowance) to determine how much elders require. The current recommendations—by both the National Research Council and the World Health Organization (WHO)—are based largely on studies conducted with healthy young men.
"The data on older people are too scanty to base a requirement on," says nutritionist Wayne W. Campbell. He led one of the studies while at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston, Massachusetts. The few studies that had been done with older people differed in their conclusions, says Campbell, who is now at Pennsylvania State University. Two found the current RDA sufficient, while three others it too low to maintain balance—that point when the amount of protein consumed just replaces the amount excreted.
It's not surprising, when one considers that the volunteers in each of the studies varied in several ways, Campbell says. Differences included their ability to function physically, calorie intake, physical activity level, health status, and medication usage. "All of these variables might alter protein requirements."
So Campbell and colleagues looked at nitrogen balance in 12 men and women—56 to 80 years old—during the first 2 weeks of a longer study. Since all proteins contain nitrogen while fats and carbohydrates do not, researchers can track protein intake and excretion by measuring nitrogen.
Half of the volunteers were given the current RDA—0.8 grams per kilogram of body weight per day (g/kg/d)—in a vegetarian diet including dairy products and eggs. The other six got the same meals, but their protein intake was doubled with a milk-based beverage.
The researchers calculated the amount of protein needed to keep the volunteers in balance using a nitrogen-balance formula adopted by WHO in 1985. On average, says Campbell, the volunteers required a little more than the current RDA—about 1 g/kg/d-just to replace the protein they excreted daily.
The researchers also recalculated protein requirements for three of the five earlier studies using the newer WHO formula and got nearly the same estimate—0.9 g/kg/d.
"We found the average protein requirement for these elderly people to be higher than for younger people," says Campbell. He points out that the RDA builds in an added safety factor to cover those who require more than average. Based on these calculations, a safe recommended protein intake for elderly adults might be 1 to 1.25 g/kg/d.
This seems to defy conventional wisdom. Older people have less muscle than younger adults, so why do they need more protein?
"It's generally thought that elders are less efficient at handling protein," Campbell explains. "Also, muscle is slower to turn over—that is, to break down and rebuild—than internal organs, such as kidneys. So as older people lose muscle mass, there's an upward shift in the relative amount of protein needed."
But the amount of protein consumed made no difference to the Boston study's main focus—to determine the impact of 12 weeks of resistance training on muscle strength, body composition, and number of calories burned. The volunteers had about the same improvements in all three categories, regardless of their protein intake.
Different Studies -- Different Results
At the ARS Grand Forks Human Nutrition Research Center in North Dakota, a group of 14 older women—51 to 70 years old—were fed diets with the same protein levels as in the Boston study. For 7 weeks each, the women ate a high-meat diet containing twice the RDA and two low-meat diets, containing the RDA.
And all of them stayed in nitrogen balance on the low-meat diets as well as on the high-meat diet, says study leader Janet R. Hunt, a nutritionist. Based on the results, she concludes, "0.8 g/kg/d meets the protein requirements of older women."
Hunt notes that this study differed from the Boston study in several ways. Meat was the main source of protein rather than milk, and all the women consumed both high and normal protein levels, so they served as their own controls.
"Perhaps, most important to the differences in nitrogen balance," says Hunt, "was that our diets provided more calories per kilogram of body weight. When people don't get enough calories to maintain weight, some of the protein will be burned for energy needs instead of being used for synthesis."
She said the Grand Forks diets averaged about 150 to 200 more calories per day than the Boston diets. That's a small difference and would account for less than a pound lost or gained in 2 weeks—a weight change that could appear to be normal fluctuation.
So the jury's still out on protein requirements for elders. More and larger studies are needed to help the RDA panel reach an informed consensus.
While the average senior citizen doesn't plan meals around the RDA's, the findings have a lot of policy effects. Nursing home and hospital menus, Meals on Wheels, and senior feeding programs are geared to the RDA's. — By Judy McBride, ARS.
"Fine-Tuning Elders' Protein Needs" was published in the July 1995 issue of Agricultural Research magazine.