What Makes a Protein "Complete"?
Proteins are composed of amino acids, and the human body requires 20 different types for proper function. Nine of these are essential, meaning the body cannot produce them and they must be obtained through diet. A complete protein source provides sufficient amounts of all nine essential amino acids. While animal products like meat and eggs are typically complete proteins, many plant-based foods are considered incomplete because they lack enough of one or more essential amino acids. However, the body can pool amino acids throughout the day, so this is generally not an issue for individuals with varied diets.
The Amino Acid Profiles of Peanut Butter and Bread
Peanut butter and bread, individually, are considered incomplete protein sources, each with a distinct amino acid profile that complements the other.
Peanut Butter's Limiting Amino Acid
As a legume, peanut butter is a plant-based protein source rich in several amino acids, but it is relatively low in the essential amino acid methionine. A two-tablespoon serving provides about 8 grams of protein and is also a good source of healthy fats, fiber, magnesium, and vitamin E.
Bread's Complementary Amino Acid
Whole-grain bread, on the other hand, is typically lower in lysine but contains a good amount of methionine. This makes whole-grain bread a complementary partner to peanut butter. When consumed together, the methionine from the bread helps compensate for the lack in peanut butter, and the lysine in peanut butter complements the bread's profile. This combination effectively creates a complete protein source.
How a PB&J Creates a Complete Protein
The process of combining incomplete protein sources to form a complete protein is known as protein complementation. It is not necessary to consume these complementary proteins in the same meal, as the body can utilize amino acids from foods eaten throughout the day. This means a whole-grain PB&J sandwich provides a complete protein source due to the combined amino acid profiles of its components.
Enhancing Your PB&J for Maximum Protein
To optimize the nutritional value of a PB&J:
- Choose Your Ingredients Wisely: Use natural peanut butter with minimal added sugar and whole-grain or sprouted bread for enhanced nutrition. Refined white bread offers fewer nutrients and less fiber.
- Boost Protein with Add-ins: Incorporate chia or hemp seeds, which are complete proteins, or mix protein powder into the peanut butter or a side drink.
- Consider Other Combinations: Enhance the protein content by adding Greek yogurt or cottage cheese.
Complete vs. Complementary Proteins: A Comparison
| Feature | Complete Proteins (e.g., Animal Sources, Soy, Quinoa) | Complementary Proteins (e.g., PB&J, Rice & Beans) |
|---|---|---|
| Definition | Contains all nine essential amino acids in sufficient amounts in a single food source. | Two or more incomplete proteins, when combined, supply all nine essential amino acids. |
| Best for | Individuals seeking a single-source protein with a balanced amino acid profile, or those with higher protein demands. | Individuals following plant-based diets or simply varying their protein intake. |
| Example Sources | Meat, poultry, fish, eggs, dairy, soy (tofu, edamame), quinoa. | Peanut butter and whole-grain bread, rice and beans, hummus and pita, lentils and nuts. |
| Nutritional Profile | Often higher in saturated fat (animal sources) but dense in protein. | Typically higher in fiber and healthy fats, with a wider array of micronutrients. |
The Final Takeaway: A Nutritious and Balanced Meal
A PB&J made with whole-grain bread functions as a complementary protein, providing all nine essential amino acids. The body's ability to utilize amino acids consumed throughout the day means complementary proteins don't need to be eaten in the same meal. Choosing whole-grain bread and natural peanut butter makes a PB&J a nutritionally sound part of a balanced diet. A varied intake of protein sources is important, especially for those on plant-based diets. A PB&J also offers healthy fats, fiber, vitamins, and minerals.
Conclusion
While a PB&J is not a complete protein on its own, the combination of peanut butter and whole-grain bread creates a complementary protein source, providing all nine essential amino acids. This makes the classic PB&J a surprisingly balanced and effective meal, particularly for plant-based diets, as part of a varied nutritional intake.
