Protein is an essential part of the human diet, and most Americans eat plenty of it.
Adults should eat a minimum of 0.8 grams of protein for every kilogram of body weight daily — that's about 58 grams for a 160-pound adult, according to recommendations from the Institute of Medicine.
"We're a meat-, poultry-, fish-focused society," said Julie Metos, a dietitian at the University of Utah. "When we think of a meal, it's usually some form of meat, surrounded by starches or veggies on a plate."
At any meal, consuming 2 to 3 ounces of cooked lean meat, poultry or fish, or half of a cup of cooked beans, is what's suggested.
Portion sizes in the U.S. are often bigger than that, Metos said.
Three ounces of protein is a serving about the size of the palm of your hand, she said. "But a hamburger at a fast food place is usually 4 ounces. And if you get a double burger, it's 8 ounces."
While eating more protein than what's recommended is not necessarily bad for you, if the excess protein in a diet is contributing to excess calories, it can contribute to weight gain.
Here are three more things you should know about protein.
A high-protein diet may help with weight loss — but only for a little while.
Although there is some evidence to suggest that high-protein, low-carb diets help people lose weight more quickly than low-fat, high-carb diets, it remains unclear if high-protein diets can work for the long term.
In a 2007 study published in the Journal of the American Medical Association, researchers looked at 311 overweight and obese women, and divided them into four groups. Each group followed either the Zone diet (which roughly balances protein, carbohydrates and fat intake), the Atkins diet (high protein, low carb), the LEARN diet (low fat), or Ornish diet (low fat) for one year.
At the end of the study, they found that women on the Atkins diet, who ate the most high-protein meals, lost about 10 pounds, while women in the other groups who lost between three and six pounds.
But experts have said that not all the women in the study stuck with their assigned diets.
Metos said that current research suggests focusing weight-loss efforts on reducing the number calories you eat. "The protein, fat and carbohydrate content is not a factor, as long as the calories are reduced."
"Some people report they feel more full with a higher-protein diet, so it could help them indirectly to lower their calorie intake, but over time it is not shown to be better," she said.
Adding more protein to your diet doesn't promote muscle growth.
In a 2004 study, researchers looked at whether adding more protein to an athlete's diet would affect performance and muscle build.
They found that while athletes — especially those involved with sports that require a lot of endurance and muscle power, such as long-distance runners or football players — may benefit from increased protein intake, most athletes in the study get enough protein from their regular diets.
Even body builders need only a little bit of extra protein, for example by intaking protein powder to support muscle growth, which they can get by eating more food, reports the National Institutes of Health.
"People who are trying to get into shape think they need more protein, so they drink protein shakes," Metos said, "but they probably don't need that at all."
Eating too much protein can be bad for your health.
The health risks of eating too much protein greatly depend on what kind of protein you eat, but some high-protein foods are also rich in saturated fat, which can raise the risk of heart disease.
"It's OK to eat a little extra protein, as long as you keep your calories in check," Metos said. "Protein has calories, so if you eat a little too much, and don't exercise, it can get stored as fat."
In a large study published in the June issue of the British Medical Journal, researchers looked at nearly 44,000 women in Sweden, who were in their 30s and 40s at the study's start, who completed dietary questionnaires. After 15 years, the study group experienced 1,270 cardiac events, such as heart attacks and strokes.
The researchers found that for every 20 fewer grams of carbohydrates that study participants ate daily, and 5 more grams of protein eaten daily, the risk of heart disease increased by 5 percent.
In addition to heart disease, studies suggest that eating high amounts of protein can contribute to high cholesterol levels, gout and may put a strain on the kidneys, especially those who suffer from kidney disease.
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