RODALE NEWS, EMMAUS, PA—Looking to lose weight after menopause? A new study suggests that going vegetarian may be a healthier alternative than trying out the more popular high-protein diets, such as Atkins. The findings, published in the Journal of Gerontology: Medical Sciences, suggest that eating a lot of meat could accelerate bone density loss in postmenopausal women, while sticking with more common protein amounts, primarily from plant and dairy sources, did not.
THE DETAILS: This two-part study involved postmenopausal women whose body mass indices defined them as either overweight or obese. For the first part of the study, 54 women were separated into two groups that went on two separate calorie-restricted diets: a high-protein diet that contained 30 percent of calories from pork and a "normal protein" diet, in which 18 percent of calories came from vegetarian sources of protein, including milk, eggs, beans, and whole grains.
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In the second study, 54 overweight or obese postmenopausal women were divided into four groups: one group that ate their normal diet with no calorie restrictions or protein requirements; a vegetarian group that got 16 percent of calories from plant, dairy, or egg protein; a beef group; and a chicken group—the last two getting 26 percent of calories from their respective animal proteins. To ensure that everyone was receiving the same amount of calcium, which can affect bone density, the high-protein dieters in both studies were given supplements that equaled the amount of calcium eaten by the vegetarian group.
In both studies, the higher-protein diets were linked with lower bone density scores, despite the fact that everyone (except the group that ate their normal diets) lost roughly the same amount of weight. While the vegetarian dieters saw no declines in bone mineral density, the high-protein meat eaters averaged a 1.4 percent decrease in densities over the course of their respective diets. In the second study, the group that didn't change its eating patterns maintained the same levels of bone density as well.
WHAT IT MEANS: Sticking to a high-protein diet could accelerate bone loss as you age. And why that is, isn't exactly clear, says the study's lead author, Wayne Campbell, PhD, professor in the Department of Foods and Nutrition at Purdue University. "The acidity that is associated with foods containing amino acids [such as meat] may promote the loss of calcium," he says. "And the way our kidneys handle that acid can influence calcium regulation." Another explanation could be that meat proteins influence the continual breakdown and buildup of bones. "Basically, all women, particularly postmenopausal women, experience a high turnover of calcium in their bones," he says. "They're always building bone and breaking down bone, and our studies suggest that bone breakdown is exceeding bone buildup in these high-protein diets."
All of these assumptions are preliminary, he adds, and shouldn't be taken to mean that everyone should go on a low-protein diet to lose weight. After all, getting inadequate protein as you diet could cause you to lose lean muscle tissue. "The same diets that appear to help retain lean muscle tissue were the diets that help promote bone loss," he says, "so it's really a balancing act."
You can find a way to retain bone mass without losing lean muscle while dieting with a few of Campbell's tips:
• Eat a variety of proteins. Campbell notes that his study wasn't designed to look at whether vegetarian proteins were somehow superior to animal proteins (the two studies were actually part of larger research into pork, beef, and weight loss), and he concedes that not everyone who wants healthy bones can or would want to adopt the vegetarian diet that he used in his study. "But for people concerned with bone health and trying to lose weight, a more reasonable approach would be to transition your diet toward more plant-based sources of protein as opposed to trying to adopt and maintain a strict vegetarian diet." In addition to eggs and dairy products, look for protein from soybeans and whole grain breads, pastas, and rice.
• Know your number. Campbell suggests getting a pre-weight-loss bone density test or osteoporosis screening before you start dieting to find out whether you're at risk for conditions like osteoporosis that might influence which type of diet (high protein or normal protein) is best for you. Ironically, women who are overweight tend to be at a reduced risk for osteoporosis, which may make high-protein diets a better alternative for them, says Campbell. "It really becomes individualized when it comes to recommendations like this," he adds.
• Aim high. Even if you do find yourself at risk of osteoporosis, it won't harm older adults to get a little extra protein now and then, says Campbell. In his studies, the normal protein diets included the USDA's recommended daily allowance of 0.8 grams of protein per kilogram of body weight per day (that's about 63.5 grams of protein—or a serving of chicken, a cup of yogurt and an egg—for a 175-pound adult). "That is the minimum amount people should be striving to consume," he says, "but there's some indication that older people may benefit from moderately higher amounts," from 1 to 1.2 grams per kilogram of body weight. That will boost your protein but won't put you in the range of losing bone mass, which in his study was 1.6 grams per kilogram of body weight.
• Take your supplements. "Our data don't suggest that taking a calcium supplement trumps the potential impact of higher animal protein diets," Campbell says, "but the general recommendation that women take calcium supplements is still very sound." He recommends a 1,200 milligram calcium supplement, accompanied by a 600 to 800 IU dose of vitamin D, to promote healthy bones, regardless of diet.