SAN FRANCISCO (CBS 5) – Muscles keep us strong, burn calories, and help us look younger –  but when middle age hits, they often disappear. An average person in middle age loses about a quarter pound of muscle every year.

Now, scientists are coming up with new strategies for to keep people strong, including loading up on protein.

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Susan Bostrom-Wong wants to stay healthy and vital, and that means keeping her muscles strong.

“It’s sort of use it or lose it or at least try to maintain it,” said the 67-year-old.

Experts have said strength training is a great way to stem muscle loss. It’s tried and true. But fitness expert Laura Greenfield said it’s not enough. Greenfield is fitness manager at the Jewish Community Center in San Francisco.

“If you don’t take in sufficient protein, your body will rob it from your muscles,” said Greenfield.

Now scientists are finding out how much of which kind of protein you eat and when you eat it may really matter as you age.

“Researchers today are actually examining whether or not if we increase our protein intake can we increase our muscle mass,” said Jo Ann Hattner.

Hattner, a registered dietician, said you should eat the amount of protein in grams equal to half your body weight.

“So if you’re 150 pounds, that would be 75 grams of protein a day,” said Hattner.

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In addition, some studies indicate older individuals may need to eat protein that contains a larger amount of a certain amino acid called leucine.

“Leucine is a very popular amino acid right now because some short term studies in older people have shown it may actually be a stimulus for protein synthesis,” said Hattner.

The foods highest in leucine include poultry, fish, and dairy, as well as whey powder.

Leucine is also found to a lesser degree in some plant proteins including tofu, nuts and beans.

Laura Greenfield cautions not everyone can eat a diet high in protein and said anytime you change your diet to check with your physician. She also believes that you should mix up your sources of protein.

“Beans are a wonderful source of plant protein the vegetable family,” said Greenfield.

As for Susan Bostrom-Wong, she’s boosted the protein in her diet as well as boosting muscles with resistance training.

“I have more energy during the day. I’m stronger,” said the 67-year-old.

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