All of your cells contain protein, but that doesn't mean they can store extra protein at will. Your body breaks down protein foods to obtain specific amino acids that support multiple functions, including growth, tissue repair and enzyme production. Although these amino acids are necessary nutrients, you don't benefit from getting more than your body can use. Your body takes the protein it needs from the foods you eat and then either burns off any excess for energy, excretes it or stores the extra calories as fat.
What You Need
Protein needs are determined by your size and activity level. The average person needs just 0.36 gram of protein per pound of body weight. If you weigh 150 pounds, you'll get plenty with about 55 grams per day -- the amount in 1 cup of chopped, cooked chicken, 1 cup of low-fat milk and two eggs. Athletes require slightly more protein to support muscle repair and growth. They should aim for between 0.5 and 0.8 gram of protein per pound of body weight daily, with endurance athletes aiming for the lower end of the range and strength-based athletes at the higher end.
Myth: More Is Better
Because the amino acids in protein support tissue repair and growth, some people believe that eating more protein can result in larger muscles. Protein alone cannot build muscle -- only stress, usually in the form of exercise, can do that. A protein snack consumed right after exercise can help encourage muscle recovery and growth, though. Your body can only use so much protein to help in this process. A study published in the "Journal of the American Dietetic Association" in 2009 found that 30 grams of protein maximally stimulated muscle protein synthesis, the process by which muscles grow and repair. A serving greater than 30 grams offered no additional benefit.
Protein Overload Effects
Too much protein can also throw off your body's nitrogen balance, which results in a high concentration of amino acids in your urine and excess stress on the kidneys and liver, notes the National Strength and Conditioning Association. When your body processes protein, ammonia is produced as a byproduct. If you eat too much protein, the body cannot eliminate this ammonia through normal means, and your sweat may start to smell like ammonia. In an attempt to keep you from overloading on protein, your body will also slow digestion of protein in your stomach when you've eaten too much, causing nausea. Because your body can't store extra protein, it has to break it down. If you consume protein too close to exercise, your body won't focus on oxygenating and hydrating your muscles optimally because it needs oxygen and water to metabolize the protein. You may end up with a poor training session or competition as a result.
Many foods contain some protein, but not all are complete proteins -- meaning they have a complete array of amino acids. Meat, poultry, fish, eggs, soy, whey and dairy are complete proteins. Vegetarian sources of protein, including beans, nuts, seeds and grains, are incomplete sources, so they are missing one or more of the essential amino acids or don't offer them in adequate ratios. Ovo-lacto-vegetarians can get plenty of protein by eating a variety of plant foods as well as dairy and eggs, throughout the day. To prevent protein overload, eat a varied diet that includes plenty of whole grains, vegetables and fruits as well as protein-filled foods.
- Iowa State University Extension: Protein
- Nutrient Timing for Peak Performance; Heidi Skolnik and Andrea Chernus
- Oklahoma State University Extension: Protein and the Body
- National Strength and Conditioning Association: Resistance Training: Benefits of Post-Exercise Consumption of Protein Supplements
- Journal of the American Dietetic Association: A Moderate Serving of High-Quality Protein Maximally Stimulates Skeletal Muscle Protein Synthesis in Young and Elderly Subjects