Which Food Has the Highest Quality of Protein?

The humble egg has long been the benchmark for protein quality, historically receiving the highest possible score on older metric scales. With advancements in nutritional science, we now use more precise methods to assess protein sources. This article explores which food has the highest quality of protein today using the modern DIAAS metric for a more accurate evaluation.

Quick Summary

An evaluation of protein quality, comparing modern DIAAS scores to older methods. The article covers top animal and plant sources, their amino acid profiles, and digestibility to determine which foods offer the most complete and usable protein for the body.

Key Points

• DIAAS is the gold standard: The Digestible Indispensable Amino Acid Score (DIAAS) is the most accurate method for determining protein quality by measuring digestibility in the small intestine.

• Eggs are a benchmark: Whole eggs provide a complete amino acid profile with high digestibility, often serving as a quality standard.

• Milk proteins score highly: Whey and casein from milk are exceptionally high-quality proteins with excellent DIAAS scores, making them ideal for muscle synthesis.

• Animal proteins top the charts: In general, animal-derived sources like milk, beef, and chicken have higher DIAAS scores than most plant proteins.

• Plant-based options exist: Soy, quinoa, and hemp are notable complete plant proteins, and combining various plant foods can provide a complete amino acid profile over the course of a day.

• Processing can improve quality: Cooking and processing can enhance the digestibility of plant proteins, increasing their overall quality.

Understanding Protein Quality

Protein quality is not just about the total grams in a food; it's about two key factors: the amino acid profile and digestibility. Your body requires nine essential amino acids that it cannot produce on its own. A "complete protein" source contains all nine of these in sufficient quantities. Digestibility refers to how efficiently your body can break down and absorb the protein's amino acids. A protein is only as good as what your body can actually use.

The Shift from PDCAAS to DIAAS

For many years, the Protein Digestibility Corrected Amino Acid Score (PDCAAS) was the standard for measuring protein quality. However, PDCAAS had a significant limitation: it measured digestibility over the entire digestive tract rather than specifically in the small intestine, where most absorption occurs. This often led to an overestimation of protein value, especially for plant-based sources.

In 2013, the Food and Agriculture Organization (FAO) introduced the Digestible Indispensable Amino Acid Score (DIAAS) as the new, more accurate gold standard. DIAAS measures protein quality based on the ileal digestibility of each individual essential amino acid, providing a truer picture of how much of each amino acid is absorbed by the body. This metric helps distinguish between different high-quality proteins more effectively.

Top Tier Animal Proteins

Animal proteins are generally considered the highest quality due to their complete amino acid profiles and high digestibility. Here are some of the top contenders based on DIAAS scoring and other nutritional metrics:

• Whey Protein: Derived from milk, whey protein is a front-runner in terms of quality. Whey protein concentrate and isolate boast high DIAAS scores, with some specialized whey complexes reaching values over 1.6. It is rapidly absorbed and rich in branched-chain amino acids (BCAAs), making it popular for muscle synthesis and recovery.
• Eggs: The whole egg remains a nutritional powerhouse with a complete amino acid profile and excellent digestibility. The DIAAS for whole, boiled egg is 1.12. It contains not only high-quality protein but also other vital nutrients like choline and vitamin B12.
• Milk: Cow's milk offers high-quality protein, with a DIAAS score of 1.14. Milk contains both casein (a slow-digesting protein) and whey (a fast-digesting one), providing a sustained release of amino acids. Sheep's milk and goat's milk have even higher protein content per serving.
• Meat and Poultry: Lean cuts of meat and skinless poultry are excellent sources of high-quality protein. Beef has a DIAAS of 1.09, and chicken breast is scored at 1.08. They are also rich in iron, zinc, and B vitamins.
• Fish: Fish, particularly fatty varieties like salmon, are high-quality protein sources that also provide heart-healthy omega-3 fatty acids. Tilapia has a DIAAS of 1.00, and salmon is cited for its excellent protein content.

High-Quality Plant-Based Proteins

While many individual plant proteins are considered "incomplete," there are exceptions and effective strategies for creating complete, high-quality protein intakes through plant-based diets.

• Soy: Soy is one of the few plant-based sources that is a complete protein, containing all nine essential amino acids. Soy protein isolate scores highly on the PDCAAS scale and has a good DIAAS score, although slightly lower than animal counterparts. Tofu and tempeh are great examples of soy products.
• Quinoa: This ancient seed is a complete protein source, providing all essential amino acids. While the quantity of some amino acids may be lower than in animal sources, it is a valuable part of a balanced plant-based diet.
• Hemp Seeds: Offering all essential amino acids, hemp seeds are another complete plant-based protein source. They also provide healthy fats and fiber.
• Protein Combining: The concept of complementary proteins is crucial for maximizing plant-based protein quality. By combining different plant foods that have complementary amino acid profiles, you can form a complete protein. For example, combining grains like rice with legumes like beans or lentils provides all essential amino acids. This doesn't need to happen in the same meal, but rather over the course of a day.

Comparison of Protein Quality (DIAAS)

Food Source	DIAAS Score (0.5-3 yr old)	Notes
Goat milk	1.24	A very high-quality dairy protein.
Cow milk	1.14	Excellent source of complete protein.
Whole egg (boiled)	1.12	A benchmark for complete, highly digestible protein.
Pork	1.13	High-quality animal protein.
Beef	1.116	Complete protein with high bioavailability.
Chicken Breast	1.08	Lean protein source, complete profile.
Fish (Tilapia)	1.00	Complete and highly digestible.
Soy Protein Isolate	0.898	Complete plant protein, good quality.
Tofu	0.97	Processed soy with high digestibility.
Chickpeas	0.83	Good plant protein, often limited by methionine.
Pea Protein Concentrate	0.822	Good plant protein source for supplementation.
Cooked Rice	0.595	Incomplete protein, needs combining with other sources.
Roasted Peanuts	0.434	Low DIAAS due to digestibility and limiting amino acids.
Wheat	0.40–0.48	Very low DIAAS, poor amino acid profile.

Factors Affecting Digestibility

Beyond the amino acid profile, digestibility plays a critical role in overall protein quality. The presence of certain compounds can affect this:

• Anti-nutrients: Some plant-based foods, particularly legumes and grains, contain anti-nutrients like phytic acid and enzyme inhibitors. These can hinder the absorption of protein and other minerals. However, proper processing like soaking, sprouting, and cooking can significantly reduce their impact.
• Processing: Heat treatment and other processing methods often improve the digestibility of plant proteins by deactivating anti-nutrients. For instance, commercial processing can make legume protein isolates highly digestible, comparable to some animal proteins.

Conclusion

Based on modern DIAAS metrics, animal-based products like whey protein, eggs, milk, and lean meats consistently rank highest in protein quality, offering complete amino acid profiles and excellent digestibility. For individuals following a plant-based diet, soy products and certain seeds like quinoa and hemp are excellent sources of complete protein. The strategy of combining complementary plant proteins is also highly effective for meeting essential amino acid needs. Ultimately, while some foods naturally provide a higher quality protein package, a well-planned, varied diet can supply high-quality protein from a range of sources. For a deeper look into the science behind DIAAS, you can read more here: Digestible indispensable amino acid score (DIAAS): 10 years on.

Takeaways for Your Diet

• Prioritize complete sources: Include animal proteins like eggs, dairy, and lean meats, or complete plant proteins like soy and quinoa in your meals.
• Practice protein combining: If relying on incomplete plant proteins, pair them with complementary sources over the day, like rice and beans or peanut butter on whole-grain toast.
• Opt for lean cuts: For animal proteins, lean meats and skinless poultry offer high protein with lower saturated fat.
• Choose processed plant options: For plant proteins, processed versions like isolates or cooked legumes can have improved digestibility and quality.
• Supplements can help: Whey protein is a top-tier supplement for those needing an extra high-quality boost, especially for athletes or individuals with increased needs.

Practical Recommendations

• Consider eggs: As a complete and highly digestible protein source, eggs are an easy, affordable addition to any diet.
• Diversify your plant intake: Ensure a wide variety of plant foods to cover all essential amino acids. For example, combine grains, nuts, and legumes.
• Cook and prepare correctly: Proper cooking and preparation can improve the nutritional value of plant proteins by breaking down anti-nutrients.

Frequently Asked Questions

Why is the DIAAS score a better measure of protein quality than PDCAAS?

The DIAAS score is superior because it measures the digestibility of individual amino acids at the end of the small intestine (ileum), reflecting what the body actually absorbs. PDCAAS measured over the entire digestive tract, which could lead to overestimating the nutritional value of some proteins.

Are all animal proteins higher quality than plant proteins?

Not necessarily, but most animal proteins, like eggs, milk, and meat, have higher DIAAS scores than individual plant proteins. However, some plant sources like soy and quinoa are complete proteins, and strategically combining different plant foods can provide a complete protein intake.

How can I ensure I get high-quality protein on a plant-based diet?

You can get high-quality protein by incorporating complete plant proteins like soy products (tofu, tempeh) and quinoa. Additionally, by combining different plant protein sources throughout the day, such as pairing legumes with grains, you can ensure a complete intake of all essential amino acids.

Why are eggs so often called the 'perfect' protein?

Eggs are an excellent source of protein because they are a complete protein with a balanced amino acid profile and high digestibility. The whole egg provides nearly seven grams of protein along with numerous other vitamins and minerals, making it a very high-quality nutritional package.

What is the role of protein powders in achieving high-quality protein intake?

Protein powders, particularly whey protein, are known for their high quality and rapid absorption, making them a popular supplement for athletes and others with high protein needs. Plant-based powders like pea and rice protein blends can also provide a complete amino acid profile.

Does cooking impact protein quality?

Cooking generally improves the digestibility of both animal and plant proteins. For many plant-based foods, heat treatment is crucial to breaking down anti-nutrients and making the amino acids more available for absorption by the body.

Which specific animal food has the highest DIAAS score?

Based on available data, special whey protein complexes can achieve the highest DIAAS scores, some exceeding 1.6. Among more common whole foods, goat milk, cow milk, and eggs score exceptionally high, all well over 1.0.