Protein

Protein is a macronutrient built from amino acids that the body uses to build and repair muscle, bone, skin, and the enzymes that drive its chemical reactions. It is supplied by foods such as chicken breast, eggs, fish, dairy, and plant sources like lentils, and most healthy adults need a minimum of about 0.8 grams per kilogram of body weight each day.

What Is Protein

Protein is found throughout the body — "in muscle, bone, skin, hair, and virtually every other body part or tissue," per Harvard T.H. Chan School of Public Health, The Nutrition Source, which notes the body relies on "at least 10,000 different proteins" to maintain its structure and chemistry, including the enzymes that power metabolic reactions and the hemoglobin that carries oxygen in blood. Per MedlinePlus, "proteins are the building blocks of life," essential for cell repair and creation and for supporting growth in children, teens, and pregnant women. Animal sources such as salmon, poultry, and eggs supply "complete" protein containing all the amino acids the body cannot make on its own, but per MedlinePlus, "you do not need to eat animal products to get all the protein you need in your diet" — combinations of plant foods such as beans, lentils, nuts, and whole grains cover the same amino acid needs. This database's most concentrated single source is soy protein isolate, an extracted/dried ingredient, reflecting how processing concentrates protein far above what whole foods typically contain per 100 grams.

Health Benefits of Protein

Per Harvard's Nutrition Source, protein's health effects depend heavily on its source, not just the total amount consumed:

• Heart disease: Replacing red meat with plant proteins such as beans, soy foods, nuts, fish, or poultry is associated with lower cardiovascular risk, per Harvard's Nutrition Source.
• Type 2 diabetes: Harvard's Nutrition Source reports that replacing red meat with nuts, legumes, and poultry is associated with a 16% to 35% lower risk of type 2 diabetes.
• Weight management: Nut consumption correlates with less weight gain over time, and legume-rich meals increase satiety, per the same source — an effect tied to protein and fiber together rather than protein alone.
• Tissue repair and growth: Per MedlinePlus, dietary protein supports the ordinary, continuous work of cell repair and creation, and is particularly important for growth in children, teens, and during pregnancy.

How Much Protein You Need

No nutrient_rda row exists in FoodData Explorer's database for Protein (nutrient_id 1003) at the time of this draft. Per Harvard's Nutrition Source, the National Academy of Medicine's Recommended Dietary Allowance (RDA) is "0.8 grams of protein for every kilogram of body weight per day" — about 50 grams daily for a 140-pound person, or 70 grams for a 200-pound person — with an acceptable range of 10% to 35% of total daily calories from protein. This 0.8 g/kg figure is a deficiency-prevention minimum rather than an optimal target. Separately, per Harvard's Nutrition Source's coverage of the 2025–2030 Dietary Guidelines for Americans, the newly released guidelines recommend a higher range of 1.2 to 1.6 grams of protein per kilogram of body weight per day — 50% to 100% more than the longstanding 0.8 g/kg RDA. No Tolerable Upper Intake Level has been established for total protein intake; Harvard's Nutrition Source notes that research has not linked the percentage of daily calories from protein to overall mortality risk, though the population-specific cautions below still apply at high intakes.

Signs of Deficiency and Excess

Per Cleveland Clinic, "protein deficiencies are rare among people who live in the U.S.," but documented signs include swelling (edema), stunted growth in children, a weakened immune system, muscle loss, bone fractures, brittle hair and dry skin, unintended weight changes, and anemia. Cleveland Clinic notes that severe deficiency typically requires an underlying cause — such as inadequate overall food intake or a chronic condition affecting appetite — rather than occurring in an otherwise well-fed, healthy population.

Excess intake is a separate concern from deficiency. Per Cleveland Clinic, very high protein intake "puts more pressure on your kidneys to filter and process" the additional nitrogenous waste protein breakdown generates, and "high-protein diets may also increase inflammation and oxidative stress." For people with healthy kidneys, moderately higher protein intake is generally not a documented problem, but going to an extreme is discouraged even in healthy individuals per the same source.

Warnings & Interactions

People with existing kidney disease are the population most consistently flagged for caution: per Cleveland Clinic, roughly 30 million Americans have kidney disease and only about 10% are aware of it, and eating a high-protein diet "puts more of a load on kidneys that are not working appropriately to begin with." Cleveland Clinic advises that people with high blood pressure, a family history of kidney disease, or other underlying health conditions talk with a healthcare provider before significantly increasing protein intake. Beyond the kidney-specific caution, no other well-documented drug or supplement interactions with dietary protein were identified in the sources reviewed for this draft.

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