Protein is more better?
But do most people need more protein to preserve or increase muscle as they age? And does extra protein help us manage our weight, satisfy our cravings, and "stay on track," as some food labels claim?
Or does a high-protein diet increase our risk of bone loss, kidney disease, and cancer?
Here's what we know so far.
How much protein should we eat? That's not an easy question to answer. Here's the latest from the frontlines of research.
Adults need 0.36 grams of protein per pound of body weight. That's the Recommended Dietary Allowance, or RDA, which is set by the Institute of Medicine (IOM). It works out to about 45 grams a day for someone who weighs 125 pounds and 70 grams for someone who weighs 195 pounds.
But some researchers are asking whether the RDA is enough for older adults.
We lose about 1 percent of our muscle each year after around age thirty. Researchers call it sarcopenia.
"We see this loss in most adults as they get older," notes Denise Houston, of the Sticht Center on Aging at the Wake Forest Baptist Medical Center in Winston-Salem, North Carolina. "Some people maintain muscle a little better than others, but the decline in muscle mass with age is pretty much inevitable."
Adequate muscle is about more than looking buff. It's critical for getting up out of a chair or car, for example, or for walking up stairs or carrying groceries or a child.
And it's not just thin older people who are at risk. "Many overweight or obese people also have sarcopenia," says Houston. "It's not visible because of their body fat, but it's just as debilitating."
However, the Institute of Medicine didn't consider how the protein we eat affects our muscles, strength, or ability to perform everyday tasks when it set the Recommended Dietary Allowances.
"The protein standard is based on studies done primarily in younger adults," explains Houston. And the studies, some of which were done more than 50 years ago, only measured how much protein you'd have to eat to balance the protein your body loses (in excreted cells, enzymes, skin, etc.) every day.
"The RDA for protein may be only a minimum for older adults," says Houston. "We need to know more about what the optimal protein intake is, especially because of the loss of muscle and physical function with age."
(Some of Houston's research has been funded by the egg industry, as well as by the National Institutes of Health, or NIH.)
Two medical organizations--the International Osteoporosis Foundation and the European Society for Clinical Nutrition and Metabolism--convened international panels of experts during the past year to review the scientific evidence for the protein requirements of older adults. (1,2)
"There's been a lot of research on protein intake and its effects on muscle synthesis and muscle function that has generated this interest," says Nicolaas Deutz, who heads the Center for Translational Research in Aging & Longevity at Texas A&M University. Deutz chaired one of the panels. (Some of Deutz's research has been funded by the dairy industry and Nestle, as well as by NIH.)
The two panels arrived at similar conclusions: To preserve muscle and stay healthy longer, older adults should eat not 0.36 grams of protein per pound, but 0.45 to 0.54 grams. ("Older" typically means age 60 and above.)
How good is the evidence to support that advice?
Some studies have observed a link between protein and muscle loss, but others haven't. For example:
* The Health, Aging, and Body Composition Study followed 2,732 men and women in Pittsburgh and Memphis for three years. (3)
"These were well-functioning, community-dwelling individuals in their 70s," says Houston, who co-authored the study. "All of them lost muscle during the study, but those who were consuming the most protein lost 40 percent less muscle than those who were consuming the least."
The "most protein" group averaged 0.54 grams per pound of body weight (which translated into 91 grams of protein a day). The "least protein" group averaged 0.36 grams per pound (57 grams a day).
* The Women's Health Initiative Observational Study (WHI-OS) followed about 24,000 women aged 65 years or older for three years. (4)
"We found a strong association between a higher protein intake and a lower risk of frailty," says lead author Jeannette Beasley, of Albert Einstein College of Medicine at Yeshiva University.
Women consuming 0.54 grams of protein per pound of body weight every day were 32 percent less likely to become frail than women consuming 0.45 grams per pound.
"Frailty is a composite of muscle strength and mobility," explains Beasley. Women in the study were considered frail if they suffered from some combination of exhaustion, poor physical function, little physical activity, and unintentional weight loss.
A further analysis of the WHI-OS, which tracked nearly 135,000 women aged 50 to 79 for seven years, showed similar results. (5)
The researchers also gave roughly 5,000 of the women tests that measured their grip strength, how fast they could walk, and how many times they could get up and sit back down in 15 seconds. The women who ate more protein did better on grip strength and standing, but not walking.
"We found that protein intake was more closely related to muscle strength than mobility," notes Beasley.
* Unlike the other studies, the Osteoporotic Fractures in Men Study of nearly 6,000 men 65 and older found that those who became frail over a five-year period consumed as much protein as those who stayed healthy. (6)
But the WHI studies were the largest, and may be the most accurate, because they analyzed urine from some of the women to estimate how much protein they ate.
Still, no observational study can prove cause and effect. No matter how hard researchers try to take other factors (like smoking, exercise, or illness) into account, something else about people who eat more protein could explain their muscle strength.
That's why investigators feed people protein to see if it affects their muscles.
"We're constantly making and breaking down muscle," explains physiologist Jared Dickinson, of Arizona State University. "Between meals we have a higher rate of breakdown, and then after meals a higher rate of synthesis."
But "older adults may not make enough muscle after meals to fully overcome the breakdown in muscle they experience between meals," adds Dickinson. "So, over the course of a day, a month, a year, older people may experience a net loss of muscle." (Some of Dickinson's research has been funded by General Mills and by a soy protein manufacturer, as well as by NIH.)
Can eating more protein help prevent muscle loss? It's not clear.
The evidence that older people make less muscle after meals than younger people comes mostly from small studies that lasted just a few hours.
For example, when 11 older adults got the amino acids in 15 grams of protein, they incorporated less of them into muscle--at least over the next 3 1/2 hours-than did eight younger adults. (7) (You'd get 15 grams of protein in two ounces of meat, chicken, or fish, or six ounces of greek yogurt.)
But with more than 15 grams, the difference between older and younger seemed to disappear. For example, Dutch researchers found that 12 older men incorporated just as much protein into muscle as 12 younger men within six hours after they were all given 20 grams of protein. (8) And U.S. researchers found the same after they gave six younger and seven older people 30 grams of protein. (9)
"Those studies only measured synthesis, not breakdown, so we don't know what the net impact on protein balance is over time," cautions researcher Wayne Campbell, a professor of nutrition science at Purdue University. (Some of Campbell's research has been funded by the beef, pork, dairy, and egg industries, as well as by NIH.)
How much protein you get at each meal may also matter. For one week, researchers fed eight people aged 25 to 55 a diet that contained 90 grams of protein a day: a low-protein breakfast (11 grams), a low-protein lunch (16 grams), and a protein-heavy dinner (63 grams). During another week, the same people were fed roughly 30 grams of protein at each meal. (10)
"Total muscle protein synthesis was about 25 percent greater when the participants ate meals that had evenly distributed protein," says co-author Doug Paddon-Jones, a physiologist at the University of Texas Medical Branch at Galveston. (Some of Paddon-Jones' research has been funded by the beef and dairy industries, as well as by NIH.)
"It's a very small initial study," he cautions, "and we didn't have anyone older than 55 participating in it."
What's more, in an earlier study by Paddon-Jones, people made no more muscle protein after eating 90 grams of protein than after eating 30 grams. (11) That may explain why people who got 30 grams of protein at each meal made more muscle than those who got just 11 grams at breakfast (less than 30), 16 grams at lunch (less than 30), and 63 grams at supper (no better than 30).
"Evenly distributing sufficient protein throughout the day is an intriguing concept," says Campbell. "But we don't know yet how significant it is and whether a short-term effect leads to actual changes in muscle or physical function or anything else related to people's well-being."
And in long-term studies, it's not clear that getting extra protein for months preserves muscle.
When Campbell fed 10 people aged 54 to 78 the RDA for protein--0.36 grams per pound of body weight--for 12 weeks, they lost thigh muscle. (12) But so far, few studies have tested whether more protein than the RDA (without exercise) prevents muscle loss or builds muscle.
And some results aren't easy to interpret. For example, researchers gave 65 frail elderly people (average age: 80) an extra 15 grams of protein or a placebo at breakfast and again at lunch every day. After six months, the protein eaters had no greater muscle mass or strength, but they did have a better "physical performance" score. (They could stand up more quickly and lift more with their legs.) (13)
What is clear: the best way to build muscle is to do strength training (see "Making Muscle").
"The science is pretty sound that strength training definitely works more robustly than the effects of protein," says Campbell. In fact, in many studies, extra protein plus strength training built no more muscle than strength training alone.
For example, when Campbell had 220 overweight or obese middle-aged men and women do nine months of strength training twice a week and aerobic exercise once a week, they gained strength and lean muscle. But those who also were given 20, 40, or 60 grams of whey protein every day were no stronger and gained no more muscle than those who took a placebo. (14)
Similarly, when other researchers had 80 adults aged 70 to 85 do strength training and take either a placebo or whey protein (40 grams a day) for six months, the whey made no difference in muscle strength or size. (15)
However, a Dutch study got mixed results. After six months of strength training, frail elderly people gained leg strength and were able to get up out of a chair faster than when they entered the study. But those who were given an extra 15 grams of protein at breakfast and lunch during the six months did no better than those who got a placebo. The group that got extra protein did gain more muscle mass, however. (16)
Campbell's bottom line: "It's wonderful marketing for companies that would like to sell high-protein breakfasts and lunches and the like, but the science on whether or not protein actually has an impact on a person's body composition or skeletal muscle, size, strength, function--we're still doing the research."
Until the evidence becomes clear, how much protein should you eat?
"Make sure you don't slide below the amount of protein that the average older person consumes," says Campbell. "That's what the two expert panels concluded."
That means shooting for 0.5 grams of protein for every pound you weigh. (See "The Protein Counter.")
"If you're trying to lose weight by eating fewer calories," adds Campbell, "make sure you're cutting carbohydrates and fats, not protein."
Others suggest that if you're older and have trouble eating enough protein--and enough food--try a protein drink.
"As we age, our appetite and satiety cues are blunted," explains Heather Leidy, a nutritional physiologist at the University of Missouri. "When you drink protein in a shake or smoothie, you don't get the same feeling of satiety or fullness that you would if you ate your protein as a solid food. So that's an excellent strategy for folks who need to get a certain amount of protein without reaching a level of fullness that stops them from eating throughout the day." (17)
(Some of Leidy's research has been funded by the beef, pork, egg, and dairy industries, General Mills, and a soy protein manufacturer, as well as by NIH.)
"Protein helps you stay on track," say the Special K granola bar boxes. "Special K cereal, shakes, meal bars, and snacks have a winning combination of protein and fiber you need to help you outsmart hunger."
"Protein: Your Secret Weight-Loss Weapon," proclaimed the headline in Women's Health magazine in 2010. "The moment it leaves your fork, protein starts winnowing your waistline."
"Dietary protein does have a modest impact on satiety in some studies, but not in others," says Campbell. (18,19)
What's more, feeling less hungry or more full may not mean you eat less. "The majority of studies don't show any impact of satiety on how much people consume at a later meal," notes Leidy.
When it comes to weight loss, it's the calories--not the amount of carbohydrate, fat, or protein--that count.
For example, 18 of 23 weight-loss trials that lasted an average of 12 weeks found no greater weight loss with higher-protein diets than with lower-protein diets.
When a meta-analysis combined the results of all 23 trials (on a total of 1,063 people), those on the higher-protein diets lost only an extra 1.7 pounds. (20)
In the most ambitious attempt so far to see if protein is a "secret weight-loss weapon," the Pounds Lost study advised 811 overweight or obese U.S. men and women to eat 750 fewer calories a day. Half were told to get 15 percent of their calories from protein; the other half 25 percent. (The trial also tested different levels of carbohydrate and fat.)
After two years, the higher-protein group had lost no more weight than the lower-protein group. By that time, though, both groups had drifted back to getting about 20 percent of their calories from protein. (21)
However, extra protein may still help dieters: "A higher-protein diet does have a more consistent effect on preserving lean body mass during weight loss," says Campbell.
In a meta-analysis of 11 studies that lasted at least 12 weeks, dieters on higher-protein diets lost 1.3 fewer pounds of lean tissue than dieters who ate less protein. (20)
"If you eat a higher proportion of your calories as protein while you're losing weight, you'll lose less lean tissue," says Campbell.
Nothing beats strength training, or resistance exercises, for building and preserving muscle.
That's why the Centers for Disease Control and Prevention (CDC) recommends that all adults do strength training at least twice a week.
That should include 8 to 12 repetitions of exercises that work all the major muscle groups: legs, hips, back, abdomen, chest, shoulders, and arms. And the exercises should be done to the point where it's hard to do more without help.
If you don't work out, start with your local Y, community center, or sports club. The CDC offers videos and written materials (cdc.gov/physicalactivity/everyone/guidelines) on how to work out at home. For a free download of simple exercises to get you started, go to NutritionAction.com/ExerciseReport.
IS PROTEIN HARMFUL?
"Animal protein is the most significant carcinogen we consume," T. Colin Campbell, professor emeritus of nutritional biochemistry at Cornell University, said in a 2005 speech. He bases that claim mostly on a series of animal studies he conducted in the 1980s and 1990s.
But the evidence in humans is weak. In fact, Campbell's own study of 6,500 adults living in China in 1983 saw none. (1)
"The China Study found essentially no significant correlation between the consumption of animal protein and the risk of cancer, despite looking at lots of different cancers," says Walter Willett, chair of the department of nutrition at the Harvard School of Public Health.
"The China Study is interesting as a description of what people were eating during that time," says Willett. "But it's only a simple correlational study that's not very informative for learning about risk factors or causes of disease."
In 2007, all of the scientific evidence on a possible link between protein and cancer in humans was reviewed by an international panel of experts. (2)
"They just did not see much of a relationship," notes Willett, who adds that he does agree with Campbell on one point: "In general, we would be better off consuming more plant proteins and fewer animal proteins."
But it's the food, not the protein, that matters. "When you look at the risk of cardiovascular disease and cancer, eating red meat looks bad, while poultry, for example, looks pretty good."
"For a long time, researchers believed that higher-protein diets, especially those that are high in animal protein, were detrimental to bones because they led to calcium loss in the urine," says University of Connecticut bone researcher Jessica Bihuniak.
"We now believe this is not what's happening, at least in the short term."
In recent short-term studies, protein increased both the amount of calcium excreted in the urine and the amount absorbed from food. (3,4) So it didn't result in a net loss of calcium.
What's more, adds Bihuniak, "there appears to be no increase in markers of bone loss when you increase dietary protein, at least in the short term."
In fact, two recent large studies found that people who ate more protein had higher bone mass and lower rates of fractures than those who ate less protein. (5)
(Some of Behuniak's research has been funded by the dairy industry, as well as by NIH.)
"Individuals who consume very large amounts of protein, particularly animal protein, risk permanent loss of kidney function," warns the website forksoverknives.com.
But the best studies don't back that up.
"In our studies of more than 5,500 people who didn't have kidney disease, higher protein intakes were not associated with impaired kidney function," says Albert Einstein College of Medicine's Jeannette Beasley.
For example, the Cardiovascular Health Study tracked more than 3,600 adults aged 65 and older for an average of six years. During that time, 27 percent of the participants suffered a rapid decline in kidney function. But the decline wasn't linked to how much protein they ate or whether it was animal or plant protein. (6)
It's a different situation for people with kidney disease, diabetes, or other chronic conditions, who may be told to eat less protein to relieve some of the strain on their kidneys from filtering the byproducts of protein metabolism, notes Beasley.
(3) J.Nutr. 141: 391, 2011.
(4) Am. J. Clin. Nutr 68: 859, 1998.
(5) Am. J. Clin. Nutr. 90:1674, 2009.
(6) Nutrition 30: 794, 2014.
* The only sure way to build muscle or slow muscle loss as you age is to do strength training.
* Shoot for a daily amount of protein in grams that's equal to half your weight in pounds.
* Don't worry about protein causing cancer, bone loss, or kidney disease.
(1) Osteoporos. Int. 24:1555, 2013.
(2) Clin. Nutr. pii: S0261,2014.
(3) Am. J. Clin. Nutr. 87:150, 2008.
(4) J. Am. Geriatr. Soc. 58:1063, 2010.
(5) J. Am. Geriatr. Soc. 67:1863, 2013.
(6) J. Gerontol. A Biol. Sci. Med. Sci. 69: 695, 2014.
(7) Am. J. Clin. Nutr. 82:1065, 2005.
(8) Am. J. Clin. Nutr. 93: 322, 2011.
(9) Am. J. Physiol. Endocrinol. Metab. 286: E321, 2004.
(10) J. Nutr. 144: 876, 2014.
(11) J. Am. Diet. Assoc. 709:1582, 2009.
(12) J. Physiol. 542(Pt 2): 631, 2002.
(13) JAMDA 13: 720, 2012.
(14) J. Nutr. 742:1532, 2012.
(15) J. Gerontol. A Biol. Sci. Med. Sci. 68: 682, 2013.
(16) JAMDA 13: 713, 2012.
(17) Horm. Metab. Res. 39: 389, 2007.
(18) J. Am. Diet. Assoc. 111: 290, 2011.
(19) Am. J. Clin. Nutr. 89: 831, 2009.
(20) Am. J. Clin. Nutr. 96:1281, 2012.
(21) N. Engl. J. Med. 360: 859, 2009.
THE PROTEIN COUNTER The Recommended Dietary Allowance (RDA) for protein is 0.36 grams for each pound you weigh. To play it safe, shoot for 0.5 grams per pound. To make it simple, divide your weight in half. That's your protein target in grams. So if you weigh 150 pounds, shoot for 75 grams of protein a day. Calories Protein(g) Chicken or turkey breast, skinless 170 34 (4 oz. cooked) (1) Beef or pork (4 oz. cooked) (1) 300 30 Salmon (4 oz. cooked) (1) 200 28 Shrimp (4 oz. cooked) 140 26 Tempeh (4 oz.) 220 21 Greek yogurt, plain, 0% (6oz.) 100 17 Morningstar Farms Grillers Prime (1) 170 17 Cottage cheese, 1% (1/2scup) 80 14 Starbucks Nonfat Caffe Latte 130 13 (grande, 16 ft. oz.) Canned tuna, light, in water 50 11 (2 oz. drained) Tofu, extra-firm (4 oz.) 110 11 Sliced deli turkey breast (2 oz.) 60 10 Soy nuts (1/4 cup) 110 9 Milk, fat-free (1 cup) 80 8 Yogurt, plain, nonfat (6oz.) 80 8 Edamame, shelled (1/2 cup cooked) 100 8 Silk Original Soymilk (1 cup) 110 8 Beans (1/2 cup cooked) (1) 120 8 Quinoa (1 cup cooked) 220 8 Spaghetti (1 cup cooked) 220 8 Cheddar or swiss cheese (1 oz.) (1) 110 7 Almond or peanut butter (2 Tbs.) (1) 190 7 Egg, large (1) 70 6 Brie or goat cheese (1 oz.) (1) 90 6 Nuts (1/4 cup) (1) 170 6 Whole wheat bread (i slice, 1.5 oz.) 100 5 Gardenburger Original (1) 110 5 Campbell's Condensed Chicken Noodle Soup 60 3 (1 cup prepared) Hummus (2 Tbs.) 70 2 Cream cheese (1 oz.) 100 2 Ice cream or frozen yogurt (1/2 cup) (1) 120 2 Silk Original almond milk or coconut 70 1 milk (1 cup) (1) (1) Average. Source: USDA National Nutrient Database for Standard Reference and company information.
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|Publication:||Nutrition Action Healthletter|
|Article Type:||Cover story|
|Date:||Nov 1, 2014|
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