Protein builds and repairs your body's tissue, but it does a great deal more than that. Proteins run almost all the chemical reactions in your cells, carry signals between organs, help defend you against infection, and move molecules around. Eating it also helps you feel full and protects muscle when you lose weight.
The word gets stuck to gym shakes, which undersells it. MedlinePlus, the US National Library of Medicine's health site, says proteins do most of the work in cells. Here are the seven jobs that matter most.
What protein does: the short answer
Every protein is a long chain built from a set of 20 amino acids. The order of those amino acids sets the shape, and the shape sets the job. When you eat protein, digestion breaks it down into amino acids and short fragments, and your cells reassemble them into whatever they need.
That means a chicken breast does not become your muscle in any direct way. It becomes a supply of parts. Nine of those amino acids must come from food, which is what a complete protein refers to.
Job 1: protein builds and repairs tissue
Structural proteins give shape and support to cells, and on a larger scale they let your body move. Muscle is the famous example, but the same is true of the connective tissue, skin, hair and nails built from proteins such as collagen and keratin.
This work never finishes. Your body is always breaking proteins down and rebuilding them, so you need a regular supply even if you never lift anything heavier than a coffee cup. Strength training tells muscle to rebuild a little stronger, and a meta-analysis of 49 trials found protein supplementation increased those gains, up to a total intake of about 1.62 g/kg a day. Our guide to how much protein you need per day turns that into grams.
Job 2: protein runs the chemical reactions in your cells
Enzymes are proteins, and according to MedlinePlus they carry out almost all of the thousands of chemical reactions that take place in cells. Without them, digesting a meal, making energy or copying DNA would be far too slow to keep you alive. If you remember one thing from this article, make it this one, because it shows why protein is more than a fitness topic.
Job 3: protein carries signals around the body
Some hormones are proteins or smaller protein-like chains. They carry messages between cells, tissues and organs. Growth hormone is one example. Insulin, which moves sugar out of the blood, is another. GLP-1, the gut hormone behind a well-known class of medications, is a short chain of amino acids as well.
Job 4: protein helps defend you against infection
Antibodies are proteins that bind to specific invaders, such as viruses and bacteria, and mark them for removal. A 2016 review of dietary protein and health lists impaired immunity among the effects of protein undernutrition. This does not mean extra protein will stop you catching a cold. It means a genuine shortage can leave your defenses short of parts.
Job 5: protein moves and stores molecules
Transport proteins bind to small molecules and carry them through cells and around the body. Hemoglobin takes oxygen from your lungs to your tissues. Ferritin stores iron. If you have ever been told your ferritin was low, you were hearing about a protein doing this job.
Job 6: protein helps you feel full after eating
A review in the American Journal of Clinical Nutrition found that higher-protein meals produced greater reported fullness and raised satiety hormones. The authors called the effect modest, and it did not reliably change how much people ate at the next meal. So protein helps, but it is not an appetite switch. It also costs more energy to process than other macronutrients, as we cover in does digesting protein burn energy.
Even a modest effect is useful when you are trying to keep weight off. One of the tips on OffRamp's home screen reads: "Hungry an hour after eating? Add protein, not restriction." The opposite instinct, eating even less, leaves you hungrier.
Job 7: protein protects muscle during weight loss
When you eat less, your body draws on its own tissue, and that includes lean mass as well as fat. The same review reported that in short, tightly controlled feeding studies, higher-protein diets led to more fat loss and better preservation of lean mass than lower-protein ones. Longer studies were less clear-cut, but this is still the job that matters most for someone in maintenance.
OffRamp is built around a single protein floor for this reason: 1.6 g per kilogram of goal weight, rounded to the nearest 5 g. There is no calorie target anywhere in the app, so protein is the one number you track.
What happens if you do not get enough protein
Serious protein deficiency is uncommon in well-fed countries, but the effects show how much rests on this nutrient. The 2016 review lists stunting, anemia, physical weakness, edema, vascular dysfunction and impaired immunity. That edema, or swelling from fluid, happens partly because blood proteins help keep fluid where it belongs.
A milder shortfall is harder to spot, and it is more likely after a big drop in appetite, whether from a GLP-1 medication, illness or ageing. We list what it tends to look like in signs you are not getting enough protein. If you notice swelling, hair loss or ongoing weakness, have it checked by a doctor instead of assuming protein is the cause. This article is general education written by a founder, not a clinician.
