What is Protein? An Easy Guide

Everything you need to know about this vital macronutrient.

The word protein comes from the Greek proteios, meaning primary. A clear sign, if ever there was one, that protein is very important. While carbohydrates tend to be the most abundant food group, protein is no less vital. 

What is Protein?

Protein, which contains four calories per gram, is made from substances called amino acids. Amino acids are best thought of as being the protein alphabet. Where we use letters to spell different words, different amino acid configurations make up different proteins. For example, when you eat chicken, your body breaks the protein down into its constituent amino acids and then turns them into what you need – be it bigger biceps or a stronger spleen. 

As mentioned, chicken is a good source of protein but then so are all types of meat, poultry and eggs. Dairy and soya are also viable protein sources. There are also many vegan protein sources. Plant foods including grains, nuts, vegetables, beans and seeds contain amino acids, so it is possible for vegans to get enough protein, although this does require more planning and organization. 

Irrespective of the type of protein you eat, they all end up in the form of amino acids that then play a vital role in the health and function of your body. 

Types of Protein

Proteins can be categorized as complete or incomplete. This refers to the types of amino acids they contain. There are 20 amino acids. Of these 20 amino acids, 8 are “essential amino acids” which means that if those 8 amino acids are in your diet, your body can make the remaining 12 (non-essential) amino acids.

  1. Complete protein. Foods that have all the essential 8 amino acids are subsequently known as complete proteins. Eating a diet rich in these foods means that your body has everything it needs to make the remaining 12 non-essential amino acids.

    Foods deemed to be complete proteins include the usual suspects of meat, fish, eggs, dairy and soya. 
  2. Incomplete protein. Plant sources of protein are typically incomplete protein. In fact, most of us would actually say these foods are not even proteins at all but sources of carbohydrates or fats. Foods that are deemed incomplete can be combined to make complete proteins – something called complementary proteins. 

    Nuts, beans, vegetables and grains contain some amino acids but not all which means they are deemed to be incomplete proteins.

Sometimes, depending on who you read, nine amino acids are listed as being essential and 11 as non-essential, but it really doesn’t matter that much. 

How Much Protein Do You Need?

The type of training you do dictates how much protein you need and can use on a daily basis. Activities that are very catabolic (result in a lot of muscle breakdown) like strength training need more protein, whereas less catabolic activities such as running or yoga require much less and sedentary people require even less protein.

If, however, you are purposely reducing your food intake with the goal of losing fat, increasing your protein intake can help preserve muscle mass which is often lost in periods of low calorie dieting. 

While a lot of focus is on how much protein you need a day, research suggests that how you space that protein intake out throughout the day is also important.

According to some studies, it’s best to distribute your protein intake evenly throughout the day, instead of having just one protein-heavy meal. For example, you might include protein with every snack or meal, so that you’re consuming protein every 3 to 5 hours, especially after workouts.1

Protein Needs Based on Weight and Activity 

Here’s how much protein you need based on your age, weight, and level of activity.234

Type of IndividualProtein per kilogram of bodyweightProtein per pound of bodyweight
Sedentary adult0.8 g0.4 g
Recreational exerciser1.1-1.6 g0.5 – 0.7 g
Endurance athlete1.3 – 1.6 g0.6–0.7 g
Growing teenage athlete1.6 – 2.0 g0.7 – 0.9 g
Adult building muscle1.6 – 1.8 g0.7 – 0.9 g
Estimated upper limit for adults2.0 g0.9 g

Is More Protein Better?

It’s a common mistake to think more is better, that more protein automatically means more weight loss, greater performance, and bigger muscles. It’s an easy conclusion to draw when you consider the marketing hype that surrounds protein powders

While protein is undeniably important, consuming above and beyond what you actually need can be counterproductive and won’t make help you gain more muscle if you aren’t following a strength training routine. Furthermore, consuming extra protein can result in a caloric surplus which will result in fat gain rather than increased muscle size.

Research on the optimal amount of protein for good health is still ongoing and the benefit of high-protein diets for weight loss and health is still being debated by experts. However, what most experts do agree on, is the importance of eating healthier protein rich-foods, which includes fish and plant-based sources of protein such as beans, whole grains, nuts, and vegetables.

Another downside of high-protein diets is that eating too much red meat or processed meats may increase the risk of high cholesterol and heart disease. Equally, skipping healthy carbs such as vegetables in favor of protein may lead to nutritional deficiencies. Too much protein can also adversely affect kidney function in people who have kidney disease.

Why is Protein Important?

Broadly speaking, your body needs protein for two main reasons, structure and function.

  • Structural proteins refer to how protein is responsible for tissue growth and repair. It makes up a large percentage of your muscle mass, skin and internal organs as well as your hair, bones and nails.
  • Functional proteins, also known as homeostatic proteins, are integral parts of enzymes and hormones – chemicals that control the way your body works. 

Both types of protein are derived from the food you eat. So next time you are chowing down some chicken breast or tofu, remember that those amino acids are not just making your muscles bigger and stronger; they’re also ensuring your body runs as healthily and efficiently as possible. 

  • Emergency energy source. In some extreme circumstances, protein is also a source of energy – although this is relatively rare. Imagine you are stranded on a desert island for a few months with nothing substantial to eat. Or if you’re a runner, on a long run and, despite having eaten plenty of carbs beforehand you’ve been going for so long that you have fully depleted your glycogen stores and are essential running on empty.

    In this situation, your body will go all “cannibal” on you and start breaking down your muscle for energy. This process, called gluconeogenesis (literally making new glucose) means you will be able to survive for longer or keep on running, albeit slowly and painfully.

Weight Loss

Protein is also useful for people on a weight loss diet as it has a very high thermal effect. What this means is that eating protein uses a lot of energy and causes a spike your metabolic rate. The thermal effect of protein is around 30 percent. So for every 100 grams of protein you eat, 30 grams worth of energy is “lost” because it is used in the breakdown and utilization of the amino acids.

This is one of the reasons people often eat more protein to lose weight, and why low carb diets such as the Keto or Paleo Diet are often very effective. 

High Protein Foods List

Below is a list of common foods that are high in protein.

FoodServing SizeProtein Content (grams)
Meat3 oz 20-24 
Fish3 oz 16 – 26 g  
Seafood 3 oz 17-21 
Tofu 3 oz 9 
Lentils ½ cup 9 
Beans½ cup 6 – 9 
Peanut butter 2 tbsp 7 
Nuts 1 oz  4 – 6 
Sunflower seeds 1 oz 5 g
Milk8 oz 8 g
Soy milk 8 oz 7 g
Regular yogurt1 cup14 g
Greek yogurt1 cup25 g
Cheese, hard1 oz 7 g
Cottage cheese, Ricotta (low fat, part-skim) ½ cup 14 g
Quinoa ⅓ cup 6 g

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