Proteins are essential molecules that perform many vital functions in your body. They are made up of smaller units called amino acids, which are linked together in long chains. There are 20 different amino acids that can combine in various ways to form thousands of different proteins. Some of these amino acids are called essential, meaning that your body cannot make them and you need to get them from food.

What Do Proteins Do in Your Body?

Proteins have many roles in your body, such as:

• Growth and maintenance: Proteins are needed for the growth and repair of your tissues, organs, muscles, skin, hair, and nails. They also help maintain fluid and electrolyte balance, acid-base balance, and blood clotting.
• Enzymes: Proteins act as catalysts for many chemical reactions in your cells. They speed up the rate of these reactions and help regulate your metabolism. For example, digestive enzymes help break down food into smaller molecules that can be absorbed and used by your body.
• Hormones: Proteins act as messengers that communicate between your cells, tissues, and organs. They help control various processes such as growth, development, reproduction, stress response, and blood sugar levels. For example, insulin is a protein hormone that helps lower your blood sugar after a meal.
• Transport and storage: Proteins help transport and store various substances in your body. They carry oxygen in your blood (hemoglobin), deliver nutrients to your cells (albumin), store iron in your liver (ferritin), and fight infections (antibodies).
• Energy: Proteins can also be used as a source of energy when carbohydrates and fats are not available. However, this is not their main function and it can have negative effects on your health if done excessively.

How Much Protein Do You Need?

The amount of protein you need depends on several factors, such as your age, sex, weight, activity level, health status, and goals. The National Academy of Medicine recommends that adults get a minimum of 0.8 grams of protein per kilogram of body weight per day¹. This is equivalent to about 0.36 grams of protein per pound of body weight per day.

However, this is only the minimum amount to prevent deficiency and may not be optimal for everyone. Some people may benefit from higher protein intake, especially those who are:

• Pregnant or breastfeeding: Protein needs increase during pregnancy and lactation to support the growth and development of the baby and the production of milk.
• Older adults: Protein needs increase with age to prevent muscle loss and maintain bone health.
• Athletes: Protein needs increase with physical activity to support muscle growth, repair, and recovery.
• People recovering from illness or injury: Protein needs increase during periods of stress or trauma to help heal wounds and fight infections.
• People trying to lose weight: Protein needs increase when following a calorie-restricted diet to preserve muscle mass and increase satiety.

The optimal protein intake for these groups may vary from 1.2 to 2.0 grams of protein per kilogram of body weight per day². This is equivalent to about 0.54 to 0.91 grams of protein per pound of body weight per day.

What Are the Best Sources of Protein?

Not all sources of protein are created equal. Some foods provide more protein than others, and some proteins are more digestible and bioavailable than others. Moreover, some foods provide more than just protein; they also contain other nutrients that are beneficial for your health.

The quality of a protein source depends on its amino acid profile and digestibility. A complete protein source contains all nine essential amino acids in adequate amounts. An incomplete protein source lacks or has low levels of one or more essential amino acids. A digestible protein source is one that can be easily broken down and absorbed by your body.

Animal-based foods such as meat, poultry, fish, eggs, dairy products, and whey are generally considered complete and highly digestible sources of protein. Plant-based foods such as beans, lentils, nuts, seeds, soy products, quinoa, buckwheat, and hemp are generally considered incomplete or less digestible sources of protein. However, you can combine different plant-based foods to get all the essential amino acids you need.

The quality of a protein source

The quality of a protein source is not the only factor to consider when choosing what to eat. You should also pay attention to the other nutrients and substances that come along with it. For example:

• Lean meats provide protein along with iron, zinc, vitamin B12, and other minerals.
• Fatty fish provide protein along with omega-3 fatty acids, vitamin D, selenium, and iodine.
• Eggs provide protein along with choline, lutein, zeaxanthin, and biotin.
• Dairy products provide protein along with calcium, phosphorus, potassium, vitamin A, and vitamin B2.
• Whey provides protein along with lactose, immunoglobulins, lactoferrin, and other bioactive peptides.
• Beans and lentils provide protein along with fiber, folate, iron, magnesium, and phytochemicals.
• Nuts and seeds provide protein along with healthy fats, fiber, vitamin E, selenium, and antioxidants.
• Soy products provide protein along with isoflavones, phytosterols, saponins, and other phytoestrogens.
• Quinoa and buckwheat provide protein along with complex carbohydrates, fiber, manganese, magnesium, and flavonoids.
• Hemp provides protein along with gamma-linolenic acid (GLA), arginine, edestin, and other cannabinoids.

As you can see, different sources of protein have different benefits for your health. Therefore, it is important to eat a variety of foods that provide protein and other nutrients. You should also choose foods that are minimally processed and low in saturated fat, trans fat, cholesterol, sodium, and added sugars.

What Are the Effects of Too Much or Too Little Protein?

Protein is essential for your health, but too much or too little can have negative consequences. Here are some of the effects of protein imbalance in your body:

• Too much protein: Excess protein intake can cause dehydration, kidney problems, liver problems, bone loss, gout, and increased risk of some cancers. It can also displace other nutrients from your diet and increase your calorie intake. The upper limit for protein intake is 35% of calories per day¹.
• Too little protein: Inadequate protein intake can cause muscle loss, weakness, fatigue, poor wound healing, hair loss, skin problems, edema, anemia, immune deficiency, and increased risk of infections. It can also affect your growth and development if you are a child or pregnant. The lower limit for protein intake is 10% of calories per day¹.

How to Optimize Your Proteins Intake

To optimize your protein intake and maximize its benefits for your health, you should follow these tips:

• Eat enough protein: Aim for at least 0.8 grams of protein per kilogram of body weight per day¹, or more if you belong to any of the groups that need more protein. Use a nutrition calculator or app to track your intake and adjust it as needed.
• Eat a variety of protein sources: Include both animal-based and plant-based foods that provide protein and other nutrients in your diet. Choose lean meats, fatty fish, eggs, dairy products, whey, beans, lentils, nuts, seeds, soy products, quinoa, buckwheat, hemp
• Eat complete proteins: Make sure you get all nine essential amino acids from your food. You can do this by eating animal-based foods or by combining different plant-based foods that complement each other. For example: rice and beans; hummus and pita bread; peanut butter and whole wheat bread; tofu and broccoli; etc.
• Eat high-quality proteins: Choose foods that are high in protein digestibility corrected amino acid score (PDCAAS), which measures the quality of a protein source based on its amino acid profile and digestibility. Foods with a PDCAAS of 1.0 are considered the best sources of protein. These include eggs, whey, casein, soy, milk, beef, chicken, fish, and rice³.
• Eat protein throughout the day: Spread your protein intake evenly across your meals and snacks. This can help you maintain muscle mass,
  prevent hunger,
  and regulate blood sugar levels. Aim for about 20 to 30 grams of protein per meal and 10 to 15 grams of protein per snack⁴.
• Eat protein after exercise: Consuming protein within two hours after physical activity can help you repair and build muscle tissue,
  enhance recovery,
  and reduce soreness. You can choose a high-protein food or a supplement such as whey or casein.

Summary

Proteins are essential molecules that perform many vital functions in your body. They are made up of amino acids that can be obtained from food or synthesized by your body. You need to eat enough protein to support your growth, maintenance, enzymes, hormones, transport, storage, and energy needs. Eat a variety of protein sources that provide different nutrients and benefits for your health. Avoid eating too much or too little protein as this can have negative effects on your body. You should optimize your protein intake by choosing high-quality proteins, eating complete proteins, eating protein throughout the day, and eating protein after exercise.

Sources:
(1) 9 Important Functions – Healthline.
(2) The Nutrition Source – Harvard T.H. Chan School of Public Health.
(3) Why Your Body Needs It – WebMD.
(4) What do they do? – MedlinePlus.