Complete Proteins Explained: Are You Deficient if Plant-Based?

Introduction

It’s hard to miss the latest trend surrounding protein in the health and wellness space. Protein is a macronutrient often highlighted as a key component in our diets needed from muscle-building all the way to weight loss (1,2). Protein is getting incorporated into almost every food imaginable, from breakfast cereals to ice cream, but not all protein is created equal. Protein can be classified as “complete” or “incomplete” based on its components. Here, we’ll dive into the science behind the different types of proteins, their sources, and risks of relying solely on vegan protein sources.

Complete vs. Incomplete Proteins

Proteins are composed of building blocks called amino acids. There are 20 different amino acids that our body uses, 11 of which can be synthesized by our bodies on their own (3). These are known as nonessential amino acids in terms of dietary requirements. The remaining 9, termed essential amino acids, must be obtained from our diet because our bodies cannot produce them. The body needs all amino acids to form functional proteins, for muscle growth, and for enzyme production (4).

A complete protein is a protein that contains all 9 essential amino acids in adequate amounts. On the other hand, incomplete proteins lack one or more of these essential amino acids or do not have them in sufficient amounts for optimal body function, which is why they were termed "incomplete" (5).

Sources of Complete Proteins

Complete proteins are primarily found in animal products such as meat, poultry, fish, eggs, and dairy (6). However, some plant-based foods like quinoa, buckwheat, soy, and chia seeds also contain all 9 essential amino acids (7). Incomplete proteins are typically found in plant-based foods.

It’s important to note that although incomplete proteins may be lacking in one or more essential amino acids, incomplete protein sources can be combined to form complete proteins. For example, rice and beans, peanut butter and whole wheat bread, and hummus and pita are classic combinations of incomplete proteins that provide a full amino acid profile when eaten together. Using rice and beans as an example, beans lack methionine but are high in lysine, while rice is low in lysine but contains methionine, so together, they form a complete protein (8). This practice, known as complementary proteins, ensures that all essential amino acids are consumed over the course of the day.

Are Incomplete Proteins Inferior to Complete Proteins?

The idea that incomplete proteins are inferior to complete proteins is really just a myth. Just because a food isn’t a complete protein doesn’t mean it lacks nutritional value or that we should avoid them. Many foods we consume regularly are incomplete proteins, but are rich in other essential nutrients. For instance, collagen is an incomplete protein because it does not have the amino acid tryptophan, yet it is renowned for its benefits for skin health, joint function, and connective tissue support (9). Similarly, plant-based proteins are often considered inferior due to their incomplete nature, but provide a host of other nutrients that support overall health. They are high in fiber, vitamins, minerals, and antioxidants, contributing significantly to a well-balanced diet (10).

Protein Risks On Plant-Based and Vegan Diets

Individuals who follow plant-based diets have a higher risk of protein deficiencies due to the difficulty in obtaining a full amino acid profile as well as the lower digestibility of plant proteins compared to animal proteins (11).

Amino Acids Lacking in Plant Proteins

Some of the most common amino acids lacking in plant-based diets include lysine, methionine, and tryptophan due to the specific amino acid profiles of most plant foods (12). Deficiencies in these amino acids can be mitigated by consuming a diverse range of plant-based foods and combining different protein sources to ensure a complete amino acid profile.

Lower Digestibility of Plant Protein

Protein digestibility, a measure of how effectively the body can break down protein and absorb it, is also a concern in those that follow vegan and plant-based diets. Plant proteins are typically less digestible than animal proteins for a variety of reasons (13):

• Structure of plant proteins: Plant proteins are more resistant to breaking down in the gastrointestinal tract.
• Fiber: Many plant-based proteins are high in fiber, which can interfere with protein absorption. While fiber is beneficial for digestion and overall health, it can reduce the bioavailability of protein.
• Anti-nutrients: Compounds such as phytic acid, tannins, and lectins are all found in plant foods and can bind to proteins and minerals, hindering their absorption. Techniques such as soaking, fermenting, and cooking can reduce the impact of anti-nutritional factors and improve protein digestibility.

Due to the lower digestibility of protein from plant-based sources, it’s sometimes encouraged for vegans and plant-based eaters to consume more protein throughout the day (14). It may also be recommended to consume a protein supplement such as a plant-based protein powder to help meet daily protein needs on a vegan or plant-based diet.

Besides protein, vegans should be mindful of other potential deficiencies such as vitamin B12, omega-3 fatty acids, and iron. A vegan multivitamin that covers all the essential vitamins and minerals that might be missing on a plant-based diet can be found here.

How Much Protein Do You Need Daily?

The recommended daily allowance (RDA) for protein is set at 0.8 grams of protein per kilogram of body weight per day for adults (15). This translates to about 0.36 grams per pound of body weight. For example, a person weighing 150 pounds would need approximately 54 grams of protein per day to meet the RDA.

While the RDA for protein is designed to prevent deficiencies and support basic functions, there is growing evidence that this amount is not sufficient for optimal health, and does not account for the increased protein needs associated with physical activity, muscle mass maintenance, or recovery from illness. The protein RDA has not been revisited or updated in almost twenty years, and many studies published since then support protein recommendations above the RDA (16).

Conclusion

While complete proteins provide all essential amino acids, incomplete proteins can also significantly contribute to our nutritional needs, especially when consumed in combination with other foods. Maintaining a balanced diet with a variety of protein sources is the best approach for covering all nutritional bases, especially on a plant-based diet. Ensuring adequate total daily protein intake, whether from animal or plant sources, is key to maintaining optimal health.

References:

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