Nutrition Diet: What is Not a High Quality Protein?

October 13, 2025 •

4 min read

While protein is a vital macronutrient, research indicates that most plant-based proteins are naturally incomplete, meaning they lack one or more essential amino acids in sufficient quantities. Understanding what is not a high quality protein is key to building a balanced and effective nutrition diet.

Quick Summary

Low-quality proteins typically feature an incomplete amino acid profile, low digestibility, or are highly processed with unhealthy additives like sugar and sodium. Individual plant sources, gelatin, and processed meats are common examples of proteins that are not considered high quality when consumed alone.

Key Points

Incomplete Amino Acid Profile: Many plant-based proteins are low-quality because they lack sufficient amounts of one or more essential amino acids.
Low Digestibility: Protein quality is affected by digestibility, with some plant proteins being less efficiently absorbed due to fiber and antinutrients.
Heavy Processing: Processed meats, protein bars with high sugar, and highly processed meat alternatives can compromise protein quality with added unhealthy ingredients.
Complementation is Key: For vegetarians and vegans, combining different plant protein sources (like grains and legumes) ensures a complete intake of essential amino acids.
Prioritize Whole Foods: The best strategy for a high-quality protein diet is to focus on whole, minimally processed foods from both animal (if applicable) and diverse plant sources.

Protein is an indispensable component of every cell in the body, serving as the building block for muscles, bones, enzymes, and hormones. However, not all dietary protein is created equal. Protein quality is determined primarily by two factors: the completeness of its amino acid profile and its digestibility. A 'high-quality' or 'complete' protein contains all nine essential amino acids (EAAs) that the human body cannot produce on its own. A protein that lacks or is low in one or more of these essential amino acids is considered 'low-quality' or 'incomplete'.

What Makes a Protein Low Quality?

Several factors can diminish the nutritional quality of a protein source, impacting its ability to support bodily functions and protein synthesis effectively.

Incomplete Amino Acid Profile

Most plant proteins are incomplete, meaning they are low in one or more of the nine essential amino acids. This missing or deficient EAA is called the 'limiting amino acid'. For example, most grains are limited in lysine, while legumes are often low in methionine. This makes it difficult for the body to create new proteins if those sources are not combined appropriately.

Low Digestibility

Protein quality is also measured by how well the body can digest and absorb it. Some plant proteins have lower digestibility compared to animal proteins due to their molecular structure and the presence of 'antinutrients,' such as phytic acid and tannins. These compounds can interfere with the absorption of protein, along with other vitamins and minerals.

Excessive Processing

Many protein-containing foods are heavily processed with added sugars, artificial sweeteners, sodium, and unhealthy fats. This heavy processing can damage the protein, reduce its bioavailability, and introduce unhealthy additives that negate any nutritional benefits. Examples include sugary protein bars, highly processed plant-based meat alternatives, and certain yogurts with high sugar content.

Examples of Foods that are Not High Quality Proteins

To make informed dietary choices, it's helpful to identify specific food items that fall short in protein quality.

Gelatin: This is a well-known example of an incomplete protein, lacking the essential amino acid tryptophan.
Processed Meats: Hot dogs, sausages, and deli meats contain protein, but often come with high levels of sodium, saturated fats, and preservatives like nitrates, which have been linked to health risks.
Many Individual Plant Sources: While valuable for overall health, individual plant sources like grains (e.g., wheat, rice), nuts, seeds, and most legumes (e.g., beans, lentils) are incomplete proteins when eaten alone. Vegans and vegetarians must combine these foods to ensure a complete amino acid intake.
Highly Processed Plant-Based Alternatives: Many meat-like products are heavily processed with protein isolates, sodium, and fillers. Reading the ingredient list is crucial to assess their true nutritional value.
Sugary Yogurts and Protein Bars: These items often hide more sugar and fat than beneficial protein. Always check the nutrition label for a balance of protein to sugar.
Whey Concentrate: As a supplement, whey protein concentrate is less refined than whey isolate and is considered a lower-quality option due to its limited refinement process.

Comparison of Protein Quality


Feature	High-Quality Protein Sources (e.g., Eggs, Milk, Lean Meats)	Low-Quality Protein Sources (e.g., Individual Plant Sources, Gelatin)
Amino Acid Profile	Complete, containing all nine essential amino acids.	Incomplete, typically lacking one or more essential amino acids.
Digestibility	High digestibility; easily broken down and absorbed by the body.	Lower digestibility due to fiber and antinutrients; absorption varies.
Processing Level	Minimally processed (e.g., whole eggs, fresh meat).	Often heavily processed with added sodium, sugar, and fillers (e.g., processed meats, protein bars).
Nutrient Density	Rich in nutrients like B12, iron, and zinc.	May contain complementary nutrients like fiber and antioxidants.
Biological Value (BV)	Higher BV, indicating more efficient protein retention by the body.	Lower BV, with less protein retained for synthesis.

How to Ensure a High-Quality Protein Intake

Achieving an optimal protein intake, regardless of your dietary preferences, requires a strategic approach. Combining different foods can create a complete amino acid profile, a principle known as protein complementation.

Combine Plant Proteins: Pair foods with different limiting amino acids. Classic combinations include rice and beans (grains and legumes) or hummus (legumes and seeds).
Diversify Your Diet: Eating a wide variety of foods, whether plant-based, animal-based, or a combination, ensures a broader intake of different amino acids.
Choose Whole Foods: Prioritize whole, unprocessed sources of protein. For animal protein, opt for lean cuts of grass-fed beef or pasture-raised chicken. For plant protein, stick to whole lentils, chickpeas, and edamame.
Supplement Wisely: When using protein powders, research high-quality options like whey protein isolate or hydrolyzed beef protein isolate, which offer better bioavailability and fewer additives.
Consider Sustainable Sources: Some fish, like wild-caught salmon, offer high-quality protein and beneficial omega-3s, while certain farmed fish may contain contaminants and fewer nutrients.

Conclusion

The quality of protein in your diet is a nuanced topic that goes beyond mere quantity. While certain foods, particularly processed products and many individual plant sources, are not a high quality protein, they are not necessarily bad for you. By understanding the principles of amino acid completeness, digestibility, and processing, you can make informed choices to improve your overall nutrition. A diet rich in a variety of whole, minimally processed protein sources, combined strategically when necessary, is the most effective path to meeting your body's needs for repair, growth, and optimal health. You can learn more about protein quality assessment from resources like the FAO guidelines on protein quality evaluation.

Food and Agriculture Organization of the United Nations (FAO) Website

Frequently Asked Questions

An incomplete protein is a food source that is low in one or more of the nine essential amino acids (EAAs) that the human body needs to obtain from its diet. Examples include most grains, nuts, and legumes when eaten alone.

No, an incomplete protein is not necessarily unhealthy. Many plant sources that are incomplete proteins, like beans and lentils, are rich in other vital nutrients like fiber and antioxidants. The key is to consume a variety of protein sources throughout the day to ensure you get all essential amino acids.

Gelatin is a protein derived from animal collagen but is missing the essential amino acid tryptophan. Because it lacks a key building block, it cannot support new protein synthesis on its own and is therefore considered a low-quality protein.

It depends on the product. While they contain protein, many are heavily processed with high levels of sodium, fillers, and additives. Whole-food plant sources like tofu or tempeh are often a better option, but it's important to check the nutrition labels on processed products.

A limiting amino acid is the essential amino acid that is present in the lowest proportion in a food relative to human needs. It essentially acts as a bottleneck for protein synthesis, limiting how much protein can be built from that food source.

By combining complementary plant protein sources, vegetarians and vegans can create a complete amino acid profile. Examples include pairing grains (like rice) with legumes (like beans), or legumes with seeds (like hummus). Eating a varied diet of whole plant foods is also crucial.

Most animal proteins are considered high-quality or complete because they naturally contain all nine essential amino acids. However, the level of processing and added unhealthy ingredients can affect the overall nutritional value, as is the case with processed meats like hot dogs.