Complete and Incomplete Proteins: Understanding the Essentials of Protein Quality

Protein is a vital macronutrient essential for various bodily functions. It’s well known that proteins are made up of  amino acids, which are often referred to as the building blocks of life. However, not all proteins are created equal. In the world of nutrition, proteins are classified into two main categories: complete and incomplete proteins. This article aims to shed light on these types of proteins, their differences, sources, and how they fit into a balanced diet.

What are Complete Proteins?

Definition and Characteristics of Complete Proteins

Complete proteins are those that contain all nine essential amino acids in sufficient quantities. These amino acids are termed “essential” because the body cannot synthesize them on its own, and they must be obtained from the diet.

Sources of Complete Proteins

Sources of complete proteins, which contain all nine essential amino acids, include both animal-based and plant-based foods. Here’s a detailed list:

Animal-Based Sources

  • Meat: Beef, pork, lamb, veal, and game meats are all complete protein sources.
  • Poultry: Chicken, turkey, duck, and other poultry products provide all essential amino acids.
  • Fish and Seafood: Salmon, trout, mackerel, sardines, shrimp, crab, and oysters are excellent sources of complete proteins.
  • Eggs: Considered one of the most perfect sources of protein, eggs contain all essential amino acids in the right proportions.
  • Dairy Products: Milk, cheese, yogurt, and other dairy products are rich in complete proteins.

Plant-Based Sources

  • Quinoa: A pseudocereal that contains all nine essential amino acids, making it a rare plant-based complete protein.
  • Soy Products: Tofu, tempeh, edamame, and soy milk are all derived from soybeans and are complete proteins.
  • Buckwheat: Another pseudocereal that is a good source of complete protein.
  • Hemp Seeds: Known for their protein content, hemp seeds contain all essential amino acids.
  • Chia Seeds: Besides being rich in omega-3 fatty acids, chia seeds also provide complete protein.
  • Spirulina: This blue-green algae is a complete protein and also rich in vitamins and minerals.
  • Amaranth: Like quinoa, amaranth is a pseudocereal and a complete protein source.
  • Nutritional Yeast: Often used as a condiment or supplement, nutritional yeast is fortified with all essential amino acids.

Importance of Complete Proteins in Diet

The importance of including complete proteins in your diet stems from their comprehensive provision of essential amino acids, which are critical for numerous bodily functions. Here’s why complete proteins are vital in the diet:

1. Muscle Repair and Growth

  • Essential amino acids are crucial for the repair, maintenance, and growth of muscle tissue. After exercise or any physical activity, the body needs these amino acids to heal and build muscle.

2. Hormone Production

  • Amino acids play a significant role in synthesizing hormones and neurotransmitters that regulate various bodily functions, including metabolism, mood, and stress responses.

3. Enzyme Function

  • Enzymes, which are proteins, catalyze most of the chemical reactions in the body. Essential amino acids are required for the synthesis and proper function of these enzymes.

4. Immune System Health

  • Complete proteins contribute to the production of antibodies and other immune system components, which help defend against infections and diseases.

5. Tissue Repair and Maintenance

  • Beyond muscle, essential amino acids are necessary for the repair and maintenance of all body tissues, including bones, skin, and organs.

6. Nutrient Absorption and Transport

  • Some proteins and amino acids are involved in transporting and storing nutrients, aiding in the absorption and utilization of vitamins, minerals, and other nutrients throughout the body.

7. Balanced Nutrition

  • Foods that are sources of complete proteins often provide other important nutrients. For example, fish is not only a complete protein but also a source of omega-3 fatty acids and vitamins D and B12.

8. Supporting a Healthy Diet

  • Including a variety of complete protein sources can help ensure a balanced and nutritious diet, especially for individuals with specific dietary needs, such as athletes, the elderly, and those recovering from illness or surgery.

Incorporating complete proteins into the diet is particularly important for those who may be at risk of protein deficiency, such as vegetarians, vegans, and older adults. However, it’s also important to balance protein intake with other nutrients and to choose lean protein sources to support overall health and wellness.

What are Incomplete Proteins?

Definition and Characteristics of incomplete Proteins

Incomplete proteins are those that lack one or more of the essential amino acids in sufficient amounts. This doesn’t mean they are inferior, but they need to be combined with other protein sources to meet the body’s amino acid requirements.

Sources of Incomplete Proteins

Incomplete proteins are foods that do not contain all nine essential amino acids in sufficient quantities required by the human body. These proteins are typically found in plant-based foods, with some exceptions. Here’s a list of common sources of incomplete proteins:


  • Rice: Both white and brown rice are incomplete proteins but can be combined with beans to form a complete protein meal.
  • Wheat: Found in bread, pasta, and cereals, wheat is a major source of incomplete protein.
  • Oats: Often consumed as oatmeal or in oat-based products, oats are a good source of protein but lack some essential amino acids.
  • Corn: Corn and corn-based products like tortillas contain protein but are not complete sources.


  • Beans: Kidney beans, black beans, pinto beans, and others are high in protein but do not alone provide all essential amino acids.
  • Lentils: A staple in many diets around the world, lentils are a good source of protein, fiber, and minerals but are incomplete in their amino acid profile.
  • Peas: Including green peas, chickpeas (garbanzo beans), and split peas, these legumes are nutritious but incomplete proteins.

Nuts and Seeds

  • Almonds, Peanuts, and Other Nuts: While rich in protein, healthy fats, and other nutrients, nuts do not contain all the essential amino acids.
  • Sunflower Seeds, Pumpkin Seeds, and Others: These seeds are nutritious snacks or salad toppings but provide incomplete proteins.
  • Flaxseeds and Sesame Seeds: Known for their health benefits, these seeds are also sources of incomplete proteins.


  • Broccoli: This nutrient-dense vegetable contains protein but not in complete form.
  • Spinach: Similar to broccoli, spinach offers some protein alongside a variety of vitamins and minerals.
  • Potatoes: Potatoes have a bit of protein but lack a complete amino acid profile.


  • Avocado: Known for its healthy fats, avocado also contains some protein, though incomplete.
  • Mushrooms: Various types of mushrooms offer protein, but like most vegetables, they do not provide all essential amino acids.

It’s important to note that while these foods may not provide complete proteins on their own, combining different sources of plant-based proteins can ensure you get all the essential amino acids. For example, eating rice with beans or hummus with whole grain bread can provide a complete protein profile, making it easier for vegetarians and vegans to meet their protein needs.


of Incomplete Proteins in a Balanced Diet

Incomplete proteins play a crucial role in a balanced diet, even though they don’t provide all nine essential amino acids individually. Their significance in nutrition can be appreciated through several key aspects:

1. Nutrient Diversity

  • Incomplete protein sources, especially plant-based ones, often come packed with a variety of other nutrients including fiber, vitamins, minerals, and healthy fats. For example, grains and legumes are rich in B vitamins and minerals like iron, zinc, and magnesium.

2. Health Benefits

  • Diets high in plant-based foods are associated with lower risks of chronic diseases such as heart disease, diabetes, and certain cancers. The fiber and phytonutrients found in these foods contribute to improved health outcomes.

3. Environmental Sustainability

  • Incorporating more plant-based sources of protein can be more environmentally sustainable than relying heavily on animal-based proteins. Plants generally require fewer resources (water, land) and produce lower greenhouse gas emissions.

4. Flexibility in Meal Planning

  • Incomplete proteins offer flexibility in meal planning, as they can be combined in various ways to create complete proteins. This is particularly important in vegetarian and vegan diets. Complementary proteins do not necessarily need to be eaten together at one meal but can be consumed over the course of a day to meet amino acid requirements.

5. Weight Management

  • Many incomplete protein sources are lower in calories and fats compared to some complete protein sources, particularly those from animals. This can be beneficial for weight management and for maintaining a healthy body weight.

6. Economical

  • Plant-based proteins often cost less than animal proteins, making them an economical choice for many households. This can make healthy eating more accessible and affordable.

7. Cultural and Culinary Diversity

  • Foods containing incomplete proteins are staples in many cultural cuisines around the world. They contribute to the diversity of the diet and allow for the exploration of different flavors and cooking traditions.

8. Accessibility

  • For those who may have dietary restrictions, allergies, or ethical concerns with animal products, incomplete proteins provide important alternatives to ensure adequate protein intake.

Combining Complete and Incomplete Proteins

The concept of protein combining was once thought to be essential at every meal for those who rely primarily on plant-based proteins. However, contemporary nutrition science suggests that it’s not necessary to combine proteins in every meal as long as a variety of protein sources is consumed throughout the day.

Wanna learn more? Read our post on Combining Complete and Incomplete Proteins

Importance for Vegetarian and Vegan Diets

For those following plant-based diets, understanding complete and incomplete proteins is crucial. It ensures that they receive all the essential amino acids needed for optimal health. Plant-based diets can meet protein requirements effectively when a variety of plant proteins are included daily.


In conclusion, both complete and incomplete proteins are essential for a well-rounded diet. While complete proteins provide all the essential amino acids in one go, incomplete proteins can be combined to achieve the same result. Understanding these types of proteins is particularly important for those following vegetarian and vegan diets, but it’s also beneficial for anyone looking to optimize their protein intake for health and wellness. The key takeaway is the importance of variety in protein sources, ensuring a balanced intake of all essential amino acids for optimal health.


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