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Dietary protein delivers nutrients known as amino acids (AAs) that are essential building blocks for all the body’s structures and functions. Your whole body is built from the AAs in your diet. Twenty total AAs occur naturally in the food you eat. Of these, nine must come from your diet—in the correct amounts and proportions—because your body can’t make them. These nine are called essential AAs. Your body uses AAs to form and maintain your muscle, bones, ligaments, and tendons, as well as organs. Insufficient dietary intake of AAs leads your body to prioritize sending AAs to build organ systems and other priority functions before building muscle.
Many people associate protein needs with growing children, but childhood muscle growth represents a daily gain of less than five grams of protein. Instead, the human body’s major protein requirement fuels something called protein turnover. Every protein in your body has a working lifespan, and just as you need to replace the windshield wipers of your car, your body needs to continuously replace proteins. Whether you are sixteen or sixty- five, your body must replace 250 to 300 grams of protein daily. The quantity and quality of protein in your diet become increasingly more important with each birthday.
When you think about the importance of dietary protein, remember this: A healthy body requires replacing the equivalent of every protein in your body four times every year.
Healthy protein turnover keeps your body strong and resilient, but as we get older this process becomes less efficient. Aging produces anabolic resistance, which reduces your body’s repair and replacement abilities. Anabolic resistance results in loss of muscle strength. But here’s the good news . . . We have discovered that increasing both daily protein and exercise can blunt this aging process. This means you can control the trajectory of the aging curve by making the right diet and exercise choices.
The aging situation becomes more complicated given that, even as your body needs more protein as you age, it also needs fewer overall calories. Your basic metabolism begins to slow down because the fuel required to run all your organs—heart, liver, kidneys, brain—as well as supporting muscle tone decreases by about 100 calories per decade. At twenty-five you need 2,200 calories, but once you reach sixty-five you only need 1,800 calories.
This shift requires a higher-quality diet, meaning foods containing more nutrients and essential AAs with each calorie you eat. That extra slice of pizza, the large French fries, or the chocolate cake may have little impact on you at twenty-five, but at sixty-five you’re likely to gain fat and to confront the complications of increased blood pressure and elevated blood sugar or blood lipids. Essential AAs build muscle, but they also help run every bodily function.
They build enzymes that:
High-quality dietary protein is essential for virtually every aspect of maintaining whole- body and muscle health for longevity.
Stimulating muscle protein synthesis (MPS)
To grow muscle tissue, your body breaks down dietary proteins into AAs. These serve as the building blocks needed to assemble new muscle proteins—a process stimulated by both resistance training and the presence of protein made available to the body through your diet, particularly foods rich in the nine AAs.
Why a higher-protein diet works
Improves metabolic health through glucose and insulin regulation: Healthy muscles are critical for metabolic health because they serve as the body’s glucose sink, helping to stabilize blood sugar and improve insulin sensitivity. Balancing protein with carbohydrates and avoiding excess carb consumption helps maintain proper glucose levels.
Enhances satiety: Dietary protein affects multiple signals. Digested more slowly than carbohydrates, protein sits in your stomach longer, making you feel full. But, more importantly, protein stimulates multiple hormone signals, including GLP- 1, PYY, GIP, and CCK, that tell your brain you have met your calorie needs.
You might recognize one of these hormones, GLP- 1, which is the basis for many popular weight- loss drugs. Protein is the natural GLP- 1 stimulator in every protein meal.
Increases thermogenesis: All calories are not equal during weight loss! Studies that Don and I have conducted show that participants consuming a higher-protein, reduced-carbohydrate diet lost more body fat and less lean body tissue than the control group consuming a high-carbohydrate, lower-protein diet similar to the Food Guide Pyramid.
Digestion and metabolism burn some calories as heat. For carbohydrates and fats, this “thermic” calorie loss totals only about 5 percent. For protein, the thermic loss totals between 15 and 20 percent. The big difference with protein may be associated with stimulating the calorie-heavy task of fueling MPS.
Stimulates muscle protein synthesis: Dietary protein is the main factor stimulating muscle protein synthesis. Every day, our bodies go through periods of eating and fasting. During fasting periods, especially overnight, all your organs, including the liver, kidneys, and heart, must maintain constant protein amounts by drawing on AAs from muscle. Every night your muscles enter a catabolic state, breaking down tissue to provide AAs for the rest of the body.
Whenever you eat your next meal (i.e., break your fast), it’s crucial to provide the AAs necessary to reverse this breakdown and trigger the anabolic (or building) state of MPS. A high-protein breakfast is especially critical during calorie restriction for weight loss.
