THE SHORT VERSION

  • Protein helps your body build and repair tissues, make enzymes and maintain immune defenses. Its work goes well beyond muscle.
  • Proteins are made of amino acids. Nine are essential, which means you need to get them from food.
  • Muscle is always being built and broken down. What you keep over time depends on the balance between the two.
  • Your needs depend on your age, activity and health. Research does not give one exact protein target for every meal.

Turn over a yogurt cup, a cereal box or a granola bar and you will find a protein number on it. A few grams here, a few more there. It is easy to treat that number like a score to collect.

But those grams stand for something your body actually uses. These two introductions set up our 14-part protein series. Before we compare one protein with another, I want to start with the work protein does inside you.

What is your body building?

Muscle gets most of the attention, but it is only part of the answer. Your body uses protein to make and maintain muscle, skin, hair, nails and blood. Antibodies, which help your immune system recognize germs, are proteins. So are many of the enzymes that run digestion. Healing a cut takes protein too.1

None of this happens once and ends. Your body is always taking proteins apart and rebuilding them. It recycles many of the amino acids and gets more from the protein you eat.1

Protein also tends to be more filling than carbohydrate or fat, which is one reason it comes up in conversations about appetite.2 Meat, fish, eggs, milk, beans, lentils, tofu and nuts can all contribute protein to your day.

Why do amino acids matter?

Every protein is a chain of smaller pieces called amino acids. Digestion breaks the chain down. Your body absorbs the pieces and joins them in new orders to make the proteins it needs. That is why amino acids are called the building blocks of protein.1

Your body uses twenty amino acids to make proteins. It can normally make eleven of them. The other nine have to come from food. These are the essential amino acids. Here, “essential” tells you where they must come from: your diet.1

A complete protein supplies all nine in amounts that meet a reference pattern of human needs. Meat, fish, eggs and milk are familiar examples. Many plant foods are relatively low in one or more essential amino acids. Eating enough protein from a variety of plant foods across the day can cover your needs.3

One essential amino acid, leucine, also helps signal muscle to build new protein. It still needs the other amino acids to do that work. Part 5 takes a closer look at leucine and why the muscle response changes with age.1

From food protein to your body’s own proteins, simplified. Only some of protein’s roles are shown.1

From food protein to your body’s own proteins, simplified. Only some of protein’s roles are shown.1

Why does muscle go up or down?

Your muscles are never still. They build new protein and take old protein apart at the same time. Building is called muscle protein synthesis. Taking apart is called muscle protein breakdown.4

Both are normal. Whether you gain, maintain or lose muscle over time depends on the balance between them. Part 4 gives that balance its own picture: a fountain with a faucet and a drain.4

Not eating enough protein can make it harder to maintain muscle. Illness, injury and long periods of inactivity can also contribute to loss. With age, losing muscle and strength can make everyday tasks harder and increase the risk of falls.5

Food and movement work together. Strength exercises give muscle a reason to adapt, while protein supplies the materials. Long periods of inactivity can make muscle less responsive to protein. Older adults may also need more protein in a meal to produce a similar muscle-building response to younger adults.6,7

What does this look like in an ordinary day?

The recommended dietary allowance for healthy adults is 0.8 grams of protein per kilogram of body weight per day. That is about 54 grams for someone who weighs 150 pounds, or 68 kilograms.8

This is a general reference for meeting basic needs, not a personal target for every situation. Age, exercise and recovery from illness can change what is appropriate.6,8

A practical place to start is to include a protein food at breakfast, lunch and dinner. That might be yogurt or eggs at breakfast, beans or tofu at lunch, and fish or lentils at dinner. The portions matter, because these foods contain different amounts of protein.

Spreading protein across meals may help. In a small study of healthy adults, a more even distribution led to higher muscle protein synthesis over 24 hours than eating most of the same daily amount at dinner.9

That does not mean protein above a fixed amount is wasted. In a 2023 study of young men after exercise, 100 grams produced a larger and longer-lasting muscle-building response than 25 grams during the 12 hours measured.10

The study does not make 100 grams a meal target. It shows why a single cutoff cannot describe every situation. For an everyday starting point, think about your whole day of eating before chasing a precise number at each meal.

When should you ask for help?

If you are losing weight or muscle without trying, or often feel weak or tired, talk with your healthcare team. If you have kidney disease, ask about your protein needs before making a large change. A registered dietitian can also help you work out an amount that fits your situation.

Back to the yogurt cup

The number on the yogurt cup tells you how much protein is in a serving. You now know what those grams are for. The next question is what they are made of, and how easily your body can use them.

Related reading

References

Educational content. The Fountain is written to explain, not to make health claims about any product. This article summarizes published peer-reviewed research. Nothing here is medical advice.

  1. Watford M, Wu G. Protein. Advances in Nutrition. 2018;9(5):651–653. https://doi.org/10.1093/advances/nmy027
  2. Leidy HJ, Clifton PM, Astrup A, et al. The role of protein in weight loss and maintenance. The American Journal of Clinical Nutrition. 2015;101(6):1320S–1329S. https://doi.org/10.3945/ajcn.114.084038
  3. Melina V, Craig W, Levin S. Position of the Academy of Nutrition and Dietetics: vegetarian diets. Journal of the Academy of Nutrition and Dietetics. 2016;116(12):1970–1980. https://doi.org/10.1016/j.jand.2016.09.025
  4. Tipton KD, Hamilton DL, Gallagher IJ. Assessing the role of muscle protein breakdown in response to nutrition and exercise in humans. Sports Medicine. 2018;48(Suppl 1):53–64. https://doi.org/10.1007/s40279-017-0845-5
  5. Cruz-Jentoft AJ, Bahat G, Bauer J, et al. Sarcopenia: revised European consensus on definition and diagnosis. Age and Ageing. 2019;48(1):16–31. https://doi.org/10.1093/ageing/afy169
  6. Deane CS, Ely IA, Wilkinson DJ, et al. Dietary protein, exercise, ageing and physical inactivity: interactive influences on skeletal muscle proteostasis. Proceedings of the Nutrition Society. 2021;80(2):106–117. https://doi.org/10.1017/S0029665120007879
  7. Moore DR, Churchward-Venne TA, Witard O, et al. Protein ingestion to stimulate myofibrillar protein synthesis requires greater relative protein intakes in healthy older versus younger men. Journals of Gerontology Series A. 2015;70(1):57–62. https://doi.org/10.1093/gerona/glu103
  8. Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: The National Academies Press; 2005. https://doi.org/10.17226/10490
  9. Mamerow MM, Mettler JA, English KL, et al. Dietary protein distribution positively influences 24-h muscle protein synthesis in healthy adults. The Journal of Nutrition. 2014;144(6):876–880. https://doi.org/10.3945/jn.113.185280
  10. Trommelen J, van Lieshout GAA, Nyakayiru J, et al. The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans. Cell Reports Medicine. 2023;4(12):101324. https://doi.org/10.1016/j.xcrm.2023.101324