What is Protein? An Essential Guide

Protein is an essential part of a healthy eating pattern, but protein consumption is not only about quantity — it’s about quality.

Proteins and the amino acids that comprise them are often referred to as “the building blocks of life.” Protein is a necessary component for our bodily functions — including fluid balance; immunoprotection; and tissue growth, repair and maintenance. Consuming the appropriate amount of protein for your gender, age and lifestyle can help combat the tolls that physical or emotional stressors take on your body. Importantly, science tells us that protein quality — where the protein comes from and the package of nutrients it provides — is more important than quantity. 

What is protein?

Protein is one of the six essential nutrients found in food; (carbohydrates, fats, vitamins, minerals and water are the others). Along with carbohydrates and fats, protein is considered a macronutrient because our bodies need it in large quantities and it provides us with caloric energy. Proteins have a wide variety of functions that are required in nearly every aspect of our body’s metabolism; they act as enzymes, hormones, structural components for our cells; antibodies; buffers (regulating pH balance); and fluid balancers. Proteins also control such cell functions as signaling, transportation, storage and more.

Proteins are composed of long chains of amino acids, of which there are 20. The order and structure of these amino acids determines their function. Some amino acids we synthesize naturally, while others — called essential amino acids — must be obtained from food. 

What is a complete protein?

The amino acids that form proteins are categorized into three groups: essential, nonessential and conditional.

  • Essential amino acids include amino acids that the body doesn’t synthesize on its own and therefore must come from exogenous sources, such as the foods that comprise our diet. The nine essential amino acids are phenylalanine, valine, threonine, methionine, tryptophan, histidine, isoleucin, leucine and lysine. A complete protein is a protein that contains all of the essential amino acids. This type of protein is sometimes referred to as a “pure protein.” Most animal products, as well as quinoa and chia seeds, are complete proteins. There are many foods that contain some, but not all, of the essential amino acids; and when these complete protein sources are consumed within a short timeframe (such as throughout the day), your body will utilize amino acids from each to obtain the complete protein components. The best way to ensure you’re getting enough essential amino acids is by eating a variety of nutrient-dense foods, which is also beneficial for your gut health
  • Nonessential amino acids are produced by our bodies without help from outside sources; these amino acids are alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine and tyrosine.
  • Conditional amino acids are in a category of their own because our bodies can produce enough of these compounds — except in times of poor health, such as illness or stress. These amino acids include tyrosine, cysteine, proline, arginine and glutamine. 

How do you know if a protein is a complete protein?

There is no way for the average shopper to identify which type of protein they’re buying from the labels or nutrition facts panel. The most successful way to obtain the amino acids your body needs is by eating a variety of high quality foods, as we discuss below. 

How much protein do I need?

Many factors impact each individual’s protein requirements, such as activity level, body size (e.g., height and weight), development stage (such as pregnancy or breastfeeding), stress level, and more. In developing healthy food patterns, a good place to start is with a general recommendation; then, tweak it to suit your needs. A good starting point for recommended protein intake is the USDA’s 2020-2025 Dietary Guidelines for Americans

The USDA recommends adults consume 10-35% of their calories from protein. (One gram of protein provides you with approximately four calories.) To understand how many calories might be appropriate for your lifestyle, the guidelines offer a table (in Appendix 2) that accounts for gender, age and activity level. Keep in mind that these recommendations are offered as a frame of reference and every person metabolizes food differently, especially in times of stress and illness, so be mindful about what works for you. Additionally, as you age, sarcopenia (the loss of muscle mass) begins to set in and your protein needs will become higher.

Here are just a few examples of the protein levels that certain groups of individuals might consider:

  • Moderately active adult women, age 26-45, are recommended to consume 2,600 calories per day, with 260-910 of those calories from protein — equating to 65-228 grams of protein each day.
  • Active males in their early thirties have a somewhat higher recommended caloric intake, of around 3,000 calories per day. A starting protein range for these individuals ranges from 75-262g of protein per day. 
  • For older individuals, especially post-menopausal women, researchers have theorized that increasing protein intake above the recommended 10-15% range of daily caloric intake could be beneficial to bone health. Similarly, a 2017 meta-analysis revealed that consistently consuming more than 15% of your daily calories in protein has a positive influence in preventing hip fractures and bone mineral density loss. However, more research is needed concerning the most beneficial protein sources. 

To recap, the formula to identify a recommended starting range for your protein intake is:

Lower end: (caloric intake x .10)/4 = # of grams of protein

Higher end: (caloric intake x .35)/4 = # of grams of protein

When should you eat protein?

It is important to space your protein intake throughout the course of the entire day, even if you are exercising or weightlifting. Our bodies do not store amino acids, so they must be created as we need them. By the same token, there is a limit to how much protein the body can absorb at once. Consuming protein throughout the day can be beneficial not only because your body needs it for every metabolic process, but because protein keeps you full — typically more so than do carbs or fats. 

After an intense workout, your body benefits from an influx of high-quality protein (in addition to carbs and fats) within 30 minutes, but neither do you need to overwhelm your body with the majority of the day’s protein immediately following a workout. 

Can you eat too much protein?

While many research studies support the theory that high-protein diets are effective for weight loss and cardiovascular health, it has also been shown that the consumption of large amounts of protein can lead to weight gain. Excess protein is converted and stored as fat in our bodies (except for the unnecessary amino acids, which are excreted in our urine). Furthermore, protein sources (such as red meat) containing high levels of saturated fats could be problematic, especially when consumed with foods high in carbohydrates.

Some medical researchers have associated a high protein diet with increased risk for kidney stones and other metabolic issues. However, most research studies do not control for the variety of protein sources, making it difficult to clarify a protein’s impact on metabolic markers. Thus, saying that consumption of “too much” protein “is negative” is still a somewhat controversial concept. 

A recent study suggested that there are temporal windows at which protein consumption is optimal for your body, based on individual biological clocks. As a general rule, most peer-reviewed medical research indicates that moderation and variety of protein consumption are keys. 

Underconsuming protein can put you at risk for stunted growth, decreased immunity and organs working less efficiently. However, most Americans are not at risk for protein deficiencies.

If you’re looking for insight on protein for diabetics, read our in-depth guide: Protein and diabetes.

The best protein sources

Not all proteins are created equal. A Harvard study of 130,000 adults, followed over a 32-year period, concluded that quality, rather than quantity of proteins consumed is the most significant factor relating to improved mortality and lower morbidity (i.e., disease frequency/severity). Similarly, a 2017 review found that different protein sources — likely due to the type and amount of additional vitamins and nutrients in each source — have varying impacts upon the risk of developing type 2 diabetes. This review found that red meat and processed meat consumption represented higher risk factors for the disease, while soy, dairy and dairy products acted somewhat preventatively.

Eating protein involves more than consuming a single nutrient; it entails consuming the package of everything that comes with it: the fats, carbohydrates, vitamins and minerals that impact your health. The best protein sources are both nutrient-dense and low in saturated fat, sodium and processed carbohydrates (i.e., sugars). 

Animal proteins (such as meat, poultry, eggs, fish and dairy) are often good sources of complete proteins, while plant-based foods are often lacking one or more essential amino acids ― although they are often more nutrient-dense than their animal counterparts. Interestingly, certain plant protein pairings can provide the materials to build complete proteins — such as rice and beans, peanut butter and whole grain bread, and beans and corn. But, whether you’re a vegetarian, vegan, omnivore — or something in between — here are three easy steps to get you started. 

  1. Choose optimal animal sources:
  • Poultry (chicken, turkey, eggs)
  • Seafood (fish, mollusks, crustaceans)
  • Red meat on a limited basis (unprocessed beef, pork, lamb, veal, goat)
  1. Get proteins from plants when possible
  • Legumes: lentils, peanuts, black beans, chickpeas, kidney beans, peas (green, snow, snap), soybeans and soy products (edamame, tempeh, tofu)
  • Nuts and seeds: almonds, pistachios, walnuts, hemp seeds, flax seeds, chia seds, pumpkin seeds, sunflower seeds
  • Whole grains: wheat, quinoa, wild rice, buckwheat, teff, millet
  1. Eat a variety of high-quality proteins

A special note on protein powders: These supplements derive from a variety of sources such as whey, pea, collagen, egg whites, and insects. As when selecting all proteins, it’s important to look at the list of ingredients (including vitamins and minerals) that accompany each scoop of protein powder. Often, these supplements contain added sugars or sugar alcohols that can impact your digestive health. These powders can be a great option for a life-on-the-go or simply to get more protein into your everyday diet, but they’re not a necessary part of healthy eating. Typically, casein, whey, egg white and soy-derived protein powders are complete proteins, but it’s not possible for consumers to be sure if this is the case because they are not regulated by the FDA. What you read on the label may not be what you get. 

How does my protein intake impact the environment?

Proteins, like every other food product, are associated with varying detrimental environmental impacts. Animal meat production is known for its high resource intensity. Beef production is the most resource-intensive of all proteins, necessitating 20 times more land and responsible for 20 times more greenhouse gas emissions per edible protein unit compared with plant-based alternatives. Chicken, pork and dairy are more resource-efficient than beef. The table below (from the World Resources Institute sustainable diets program) provides a snapshot of the environmental impact and associated costs of each common protein type.

Key Takeaways

Shifting your food habits toward the consumption of high-quality proteins can help with weight management, energy levels, satiety, immunoprotection, and tissue growth and repair. Furthermore, high-quality proteins are associated with living a longer and healthier life, thanks in part to the vitamins and minerals often contained in protein-rich food sources. Additionally, high-quality proteins are typically low in saturated fats, processed carbohydrates and sugars — food types most associated with cardiovascular and metabolic disorders. The surest way to consume proteins that contain the essential amino acids you need, regardless of your dietary preferences, is by eating a variety of the nutrient-dense foods we list above. If you’re not sure how much protein you should be eating, the guides supplied in this article are a great starting point.

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