Protein has become a marketing keyword in the United States. It appears in cookies, chips and sweetened drinks. Influencers promote high-protein diets to build muscle. Yet recent data indicate most American adults already consume sufficient amounts. The focus is shifting. Experts now point to protein quality, not quantity, as the real issue, a topic explored in detail here.
Table of contents
- Joseph Matthews and University of Arkansas for Medical Sciences data
- Rob Wolfe and 2021 randomized protein study
- Donald Layman and EAA-9 tool at University of Illinois Urbana–Champaign
- Glenda Courtney-Martin and University of Toronto dietary recommendations
Joseph Matthews and University of Arkansas for Medical Sciences data
Protein intake in the United States
Most adults in the United States already meet or exceed recommended protein intake levels. Joseph Matthews, a nutritionist at the University of Arkansas for Medical Sciences in Little Rock, states clearly that Americans “don’t have a protein issue.” Instead, he and other specialists highlight the importance of selecting appropriate protein sources.
Current U.S. dietary guidelines recommend 1.2 to 1.6 grams of protein per kilogram of body weight per day. These guidelines assume that:
- 1 ounce of meat
- 1 cooked egg
- 1/4 cup of cooked beans
- 1 tablespoon of peanut butter
provide equivalent protein value.
Emerging evidence disputes this assumption. Rob Wolfe, a metabolism expert at the same institution, explains that foods with identical protein totals “aren’t equivalent.” He adds, “We should pay attention to the quality of protein.”
Rob Wolfe and 2021 randomized protein study
Animal versus plant protein efficiency
Proteins consist of long chains of amino acids. The human body requires 20 amino acids. It can synthesize 11. The remaining 9 are essential and must come from food.
Animal-based foods such as beef, chicken, fish, milk and eggs contain all essential amino acids in substantial amounts. Most nuts and beans lack one or more. Digestibility also differs. The body generally breaks down animal proteins more efficiently than plant proteins, increasing bioavailability.
In 2021, Wolfe participated in a randomized study involving 56 participants aged 18 to 40. Each person consumed one of seven protein sources:
- Beef sirloin
- Pork loin
- Eggs
- Kidney beans
- Peanut butter
- Tofu
- Mixed nuts
Although each portion met U.S. guideline protein amounts, blood analyses showed differences. Participants who consumed animal products produced more muscle protein than those assigned plant-based options. The findings demonstrated unequal biological efficiency despite equal labeled protein content.
Donald Layman and EAA-9 tool at University of Illinois Urbana–Champaign
Essential amino acids as measurement
Donald Layman, who studies nutritional biochemistry at the University of Illinois Urbana–Champaign, argues that protein guidelines should center on essential amino acids rather than total protein. He states, “What we have is a requirement for nine essential amino acids.”
To that end, his team built a tool called EAA-9. That’s short for nine essential amino acids. It calculates how well foods help people get the ones they need.
Examples from their data show stark contrasts.
| Food item | Limiting amino acid | EAA-9 score |
|---|---|---|
| Egg | Histidine | 15.77 |
| Peanut butter (1 tbsp) | Lysine | 4.04 |
A single egg delivers about 25 percent of several amino acids but only 15.77 percent of histidine, limiting its usable protein value to that percentage. Peanut butter scores significantly lower due to lysine deficiency. According to the EAA-9 scale, one would need roughly four tablespoons of peanut butter to match the usable protein benefit of one egg.
Layman’s team published these findings in the July 2025 Journal of the Academy of Nutrition and Dietetics.
Orthopedic surgeons Brad Weening and Paul Zalzal discuss how the body uses protein and why it should be eaten several times a day:
Video: YouTube / channel Talking With Docs
Glenda Courtney-Martin and University of Toronto dietary recommendations
Plant combinations and health outcomes
Glenda Courtney-Martin, a nutrition scientist and dietician at the University of Toronto Hospital for Sick Children in Canada, emphasizes balance. She states, “It’s about overall nutrition.” Broader context on diet and micronutrients can be found in research on vitamin supplements.
She also notes practical strategies. Combining foods with complementary amino acid profiles improves quality. For example:
- Legumes are low in methionine but high in lysine.
- Rice has the opposite profile.
- Beans and rice together provide a complete amino acid pattern.
Processing methods such as soaking and fermentation increase digestibility. Substituting rice with other cereals is discussed further zobacz tutaj.
Health and environmental data further influence recommendations. High meat intake is associated with cardiovascular disease and certain cancers. Livestock production contributes greenhouse gases and land use pressure. Researchers in 2019 advised diets centered on plant foods, limited seafood and poultry, and minimal red meat such as beef.
Courtney-Martin underscores daily structure. She advises that young people include protein at every meal and prioritize minimally processed foods prepared at home. She explains that balanced meals should include:
- Protein sources
- Fruits and vegetables rich in vitamins
- Cereal grains for carbohydrates and fiber
- Dairy or calcium alternatives
Nutrition affects growth, immune resilience and long-term health outcomes, particularly in young populations.
Current research indicates that while total protein intake in the United States is generally sufficient, amino acid composition and digestibility determine biological effectiveness. The distinction between quantity and quality is shaping ongoing revisions to dietary science.
FAQ
Do most adults in the United States consume enough protein?
Yes. Most adults in the United States already meet or exceed recommended protein intake levels. According to Joseph Matthews from the University of Arkansas for Medical Sciences, Americans “don’t have a protein issue,” but rather a question of protein quality.
What is the recommended daily protein intake in the United States?
Current U.S. dietary guidelines recommend 1.2 to 1.6 grams of protein per kilogram of body weight per day. These guidelines assume equal value between sources such as meat, eggs, beans and peanut butter.
Are animal proteins more efficient than plant proteins?
Yes. Research shows that animal-based proteins are generally digested more efficiently and provide higher bioavailability of essential amino acids than most plant-based proteins. In a 2021 randomized study involving 56 participants aged 18 to 40, those consuming animal products produced more muscle protein than participants assigned plant-based options.
What are essential amino acids?
The human body requires 20 amino acids to function properly. It can produce 11 on its own. The remaining 9 are essential amino acids and must be obtained from food. The balance of these amino acids determines the biological quality of dietary protein.
What is the EAA-9 tool developed by Donald Layman?
The EAA-9 tool measures how effectively foods provide the nine essential amino acids. For example, an egg has an EAA-9 score of 15.77 due to histidine limitations, while one tablespoon of peanut butter scores 4.04 because of low lysine content.
Can plant-based diets provide high-quality protein?
Yes. Combining plant foods with complementary amino acid profiles, such as beans and rice, can provide a complete amino acid pattern. Processing methods like soaking and fermentation can also improve digestibility.
Is protein the only nutrient that matters in a balanced diet?
No. As Glenda Courtney-Martin emphasizes, “It’s about overall nutrition.” Balanced meals should include protein sources, fruits and vegetables, cereal grains and calcium-rich foods to support growth, immune function and long-term health.
Source: Science News Explorer