Is Peanut Butter on Whole Wheat Bread a Complete Protein?

Decades ago, a popular nutrition book propagated the now-debunked myth that plant proteins must be combined in the same meal to form a complete protein. So, is peanut butter on whole wheat bread a complete protein when paired, or does the body handle things differently?

Quick Summary

This article explores the amino acid composition of peanut butter and whole wheat bread to determine if their combination creates a complete protein. It clarifies the outdated concept of protein combining with the modern understanding of the body's amino acid pool and provides additional nutritional context for this popular food pairing.

Key Points

• Not needed in one meal: It is a myth that complementary proteins, like those in peanut butter and whole wheat, must be consumed simultaneously to form a complete protein.

• Amino acid pool: The body maintains a pool of amino acids, allowing it to combine essential amino acids from different meals throughout the day.

• Complementary proteins: Peanut butter (a legume) is low in methionine, while whole wheat bread (a grain) is low in lysine; combined, they complement each other’s amino acid profile.

• Balanced nutrition: Beyond protein, this combination provides a healthy mix of fiber, healthy fats, and complex carbohydrates for sustained energy.

• Variety is key: For most people, consuming a varied diet of different plant-based protein sources is a reliable way to ensure adequate intake of all essential amino acids.

• Better with whole foods: Using whole wheat bread and natural peanut butter without added sugars or oils offers the best nutritional benefits compared to processed versions.

What Defines a "Complete Protein"?

A complete protein contains all nine essential amino acids—histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine—which the body cannot produce. These must be obtained from food. Incomplete proteins are low in or lack one or more essential amino acids. While animal foods are typically complete proteins, the distinction for plant foods has evolved.

Deconstructing the Peanut Butter and Whole Wheat Combo

Neither peanut butter nor whole wheat bread is a complete protein on its own. Peanut butter is low in methionine, while whole wheat bread is low in lysine. Combining them creates a complementary protein pairing, where the strengths of one balance the weaknesses of the other, providing a full spectrum of amino acids.

Peanut Butter: The Legume Component

Peanut butter provides protein, fiber, and healthy fats. A two-tablespoon serving offers about 8 grams of protein. Its main limitation is the amino acid methionine. However, it remains a nutrient-dense and affordable protein option.

Whole Wheat Bread: The Grain Component

Whole wheat bread offers protein, fiber, complex carbohydrates, iron, and B vitamins. As a grain, it complements legumes like peanut butter by providing higher levels of methionine. Choosing whole wheat is important for maximizing nutrients.

The “Complementary Protein” Myth Debunked

Older advice suggested combining incomplete proteins in the same meal. However, modern science shows the body uses an amino acid pool, drawing from various foods consumed throughout the day. Therefore, a varied plant-based diet provides all essential amino acids without needing specific pairings in every meal.

Comparison of Protein Sources

This table compares the protein profiles of peanut butter, whole wheat bread, and other sources.

Feature	Peanut Butter (Legume)	Whole Wheat Bread (Grain)	Complete Plant Protein (e.g., Quinoa)	Animal Protein (e.g., Chicken)
Completeness	Incomplete (low in methionine)	Incomplete (low in lysine)	Complete (all 9 essential amino acids)	Complete (all 9 essential amino acids)
Key Amino Acid	Good source of lysine	Good source of methionine	Well-balanced profile	Well-balanced profile
Synergy	Complements whole grains	Complements legumes	No pairing required	No pairing required
Other Nutrients	Healthy fats, fiber, vitamins E & B3	Fiber, complex carbs, B vitamins, iron	Fiber, magnesium, phosphorus	Iron, B vitamins, zinc
Primary Use	Spread, snack, flavor	Base for sandwiches	Salads, bowls, side dish	Entrée, main protein source

Beyond the Myth: Broader Nutritional Picture

While the strict meal-by-meal pairing isn't necessary, the peanut butter and whole wheat sandwich is still a healthy choice, offering protein, healthy fats, complex carbohydrates, and fiber. This combination contributes to satiety and provides sustained energy. For plant-based diets, focusing on complementary proteins throughout the day is a sound strategy.

Complementary Plant-Based Pairings

Many plant food combinations provide complementary proteins over the day:

• Grains and Legumes: Beans and rice, hummus and pita bread.
• Grains and Seeds: Oatmeal with hemp or chia seeds.
• Legumes and Nuts/Seeds: Salad with chickpeas and sunflower seeds.

How to Maximize Protein Intake on a Plant-Based Diet

• Eat a variety of plant foods: Include whole grains, legumes, nuts, seeds, and vegetables for diverse amino acids.
• Incorporate complete plant proteins: Foods like quinoa, soybeans, buckwheat, and hempseed are complete proteins.
• Utilize protein powders: Vegan options can supplement intake, particularly for active individuals.
• Focus on whole foods: Choose less processed grains and legumes for maximum nutrition.

Conclusion

While peanut butter and whole wheat bread are a great source of complementary proteins, the body's amino acid pool means they don't need to be consumed in the same meal. A varied diet with different plant-based protein sources throughout the day is sufficient for most people to get all essential amino acids. Enjoy your sandwich knowing it's nutritious, but don't rely solely on it for all your complete protein needs.

Visit Forks Over Knives for more information on the myth of complementary protein.

Frequently Asked Questions

Does eating peanut butter and whole wheat bread together form a complete protein?

Yes, when paired, peanut butter and whole wheat bread complement each other to form a complete protein by providing all nine essential amino acids. However, the body's amino acid pool means they don't need to be eaten at the exact same time.

What is the difference between a complete and incomplete protein?

A complete protein contains all nine essential amino acids that the body cannot produce on its own, while an incomplete protein is low in or lacks one or more of these amino acids.

Is the idea of combining plant proteins at every meal still relevant?

No, this is an outdated myth based on early nutritional science. The human body is efficient at combining amino acids from various foods consumed throughout the day, thanks to its amino acid pool.

What amino acid is limiting in peanut butter?

Peanut butter, being a legume, is low in the essential amino acid methionine.

What amino acid is limiting in whole wheat bread?

Whole wheat bread, a grain, has lower levels of the essential amino acid lysine.

What are some other examples of complementary plant-based protein combinations?

Examples include rice and beans, hummus and pita bread, and a salad with chickpeas and sunflower seeds.

Are there any plant-based foods that are complete proteins on their own?

Yes, some plant-based foods are naturally complete proteins. These include quinoa, soy products (tofu, edamame), and buckwheat.