What is Protein?

Protein ranks as the second most prevalent molecule in the body’s fat-free tissues, following water. It plays a crucial role in various bodily functions, including:

• pH Balance
• Energy Production
• Cell Signaling
• Nutrient Transport

Amino acids, the fundamental building blocks of proteins, consist of carbon, hydrogen, oxygen, and nitrogen. The structure of proteins can be elaborated in several ways (prepare for some technical jargon):

1. Primary Structure: The sequence of amino acids in a chain.
2. Secondary Structure: The folding patterns within the protein chain, typically forming alpha helices or beta sheets.
3. Tertiary Structure: The overall three-dimensional shape of a single protein molecule, shaped by amino acid interactions.
4. Quaternary Structure: Some proteins are made up of multiple polypeptide chains, which together form this structure.

In essence, proteins are chains of amino acids, referred to as peptides. While a protein can consist of just two amino acids (known as a dipeptide), most proteins comprise a minimum of 50 amino acids (termed polypeptides).

Amino Acids: Categories and Importance

Amino acids can be classified into three main categories:

1. Essential Amino Acids: These cannot be synthesized by the body and must be obtained through diet. There are nine essential amino acids, including three branched-chain types:
   • Histidine
   • Lysine
   • Methionine
   • Phenylalanine
   • Threonine
   • Tryptophan
   • Isoleucine (branched-chain)
   • Leucine (branched-chain)
   • Valine (branched-chain)
2. Conditionally Essential Amino Acids: Typically non-essential, these can become essential under specific circumstances, such as injury. They include:
   • Arginine
   • Cysteine
   • Glutamine
   • Glycine
   • Proline
   • Tyrosine
3. Non-Essential Amino Acids: These can be produced by the body, often from essential amino acids. They include:
   • Alanine
   • Asparagine
   • Aspartic Acid
   • Glutamic Acid
   • Serine

Additionally, amino acids can be classified based on their metabolic fate: glucogenic or ketogenic, indicating whether they convert into glucose or ketones for energy. This conversion is particularly evident in low-carb scenarios, such as a ketogenic diet.

Among humans, only leucine and lysine are strictly ketogenic. Leucine is pivotal for muscle development as it activates a process known as mTOR (mammalian target of rapamycin). This topic could warrant its own discussion, so let me know if you’re interested in learning more!

The remaining amino acids are primarily glucogenic. Here’s a useful chart to clarify this.

The Significance of Protein in Bodily Functions

While we've touched on a few functions of protein, its importance extends beyond those mentioned. Let’s explore additional roles that protein plays in our bodies:

• Cellular Structure and Repair: Proteins are essential for maintaining cellular integrity and repairing tissues, especially muscle.
• Enzymatic Functions: Proteins serve as enzymes, facilitating and regulating biochemical reactions, crucial for digestion, energy production, and molecule synthesis.
• Hormonal Regulation: Certain proteins act as hormones or assist in hormone production. Insulin and oxytocin are notable examples.
• Immune System Support: Antibodies, which are proteins, help identify and neutralize pathogens, bolstering our immune defenses.
• Transportation of Molecules: Proteins are key players in transporting various substances throughout the body, such as hemoglobin, which carries oxygen.
• Fluid Balance and pH Regulation: Proteins help maintain fluid levels in cells and tissues and act as buffers to regulate pH.
• Neurotransmission: Proteins are crucial for the nervous system’s functionality; neurotransmitters like norepinephrine are proteins.
• Muscle Contractions: Muscle proteins like actin and myosin are essential for contraction. Sufficient protein intake is vital for muscle mass and strength.

Evaluating Protein Quality

Does the type of protein matter? Absolutely.

High-quality proteins are typically complete, containing all nine essential amino acids. In contrast, lower-quality proteins may lack some or not be as easily absorbed by the body. Higher quality proteins are found in meats, particularly chicken, turkey, and lean cuts of red meat. Eggs also provide excellent quality protein along with omega-3 fatty acids, which stabilize blood sugar.

For those following a vegan diet, soy stands out as the best protein source, being complete and high in protein content. Other notable vegan sources with complete protein include:

1. Soy: Particularly edamame and tofu, both excellent sources.
2. Quinoa: A complete protein but lower in protein content compared to soy.
3. Chia Seeds: Contain complete proteins and are rich in omega-3s.
4. Hemp: Also a complete protein and contains BCAAs.

It’s important to consider how plant proteins are processed, as this affects their bioavailability. Cooking, fermenting, or using other methods can improve absorption.

A Quick Note on Soy: There’s some debate about soy’s phytoestrogens and their potential effects on health. However, evidence suggests that moderate consumption of soy is safe for most people and may even be beneficial for women in perimenopause and menopause.

Protein's Role in Muscle Health

You’ve likely heard that protein is crucial for building and maintaining muscle. However, there’s much discussion about the optimal amount of protein needed for muscle maintenance and growth.

During fasting, protein breakdown can occur in muscles, which can help eliminate old cells. The concern arises when protein intake is insufficient, especially without resistance training. Research indicates that resistance training can mitigate muscle loss during fasting.

Recommended Daily Allowance (RDA): The current RDA for protein is 0.8 grams per kilogram of body weight. However, for muscle growth, studies suggest an intake of up to 2.2 grams per kilogram may be more effective.

The takeaway? Prioritize protein intake, especially if you’re engaging in resistance training or aiming to build muscle.

Protein & Weight Loss

Research indicates that protein can enhance feelings of fullness, aiding those on calorie-restricted diets. It also boosts thermogenesis, meaning protein requires more energy to digest, potentially increasing calorie expenditure.

However, individual responses to protein can vary. Some may find that combining protein with fats provides better satiety. Rapidly digesting proteins, like whey and soy, are particularly effective at increasing fullness.

To sum it up, increasing your protein intake and ensuring it’s complete is beneficial. Resistance training during intermittent fasting can help prevent muscle loss, making strength training essential for overall health.

For further information on protein sources, refer to the USDA FoodData Central website.