What Is Protein and Why Your Body Needs It
Updated: Monday, February 16, 2026
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We believe that lasting health isn’t about perfection—it’s about steady, science-backed changes that compound over time. And if there’s one foundational tweak nearly everyone benefits from, it’s optimizing protein.
Protein isn’t only about building muscle; it’s about repairing tissue, regulating metabolism, producing hormones, and giving your body the raw materials it needs to thrive. Yet many people unknowingly fall short of their protein needs—leading to fatigue, cravings, slower metabolism, and muscle loss.
Before we dive into “how much” or “what kind,” let’s start with the basics:
What is protein, really? And why does your body depend on it so completely?
What Is Protein? The Science Explained Simply
Protein is a macronutrient made up of amino acids, often described as the “building blocks of life.” These amino acids link together through peptide bonds to form long chains that fold into complex shapes, each structure determining the protein’s job inside your body—whether that’s repairing muscle fibers, creating enzymes, producing hormones, or transporting nutrients (Albert et al., 2002)1.
There are 20 amino acids, and your body can’t make nine of them. These are called essential amino acids (EAAs), and you must get them from food.
Why Protein Matters: Beyond Muscle
Protein plays dozens of irreplaceable roles, including:
- Maintaining muscle tissue
- Supporting immune function
- Producing enzymes and hormones
- Facilitating neurotransmitter synthesis
- Building skin, nails, connective tissue, and bones
- Regulating metabolic rate via the thermic effect of food (TEF)
Carbohydrates and fats matter too—but protein is the nutrient your body struggles most to store.
Which brings us to…
Nitrogen Balance: Measuring Whether You’re Getting Enough Protein
Protein is the only macronutrient containing nitrogen. This allows researchers to track whether you’re breaking down more tissue than you’re building.
- Positive nitrogen balance → building/repairing tissue
- Negative nitrogen balance → muscle loss, under-recovery, poor immune function
Chronic negative balance is common in:
- People who undereat
- Dieters
- Older adults experiencing anabolic resistance
- Individuals under chronic stress or illness
Protein sufficiency is not optional—it’s fundamental.
Muscle Protein Synthesis (MPS) and the Leucine Trigger
To build or maintain muscle, you must stimulate muscle protein synthesis—your body’s process of repairing and strengthening muscle fibers.
But here’s the catch:
You need enough of one specific amino acid—leucine—to “flip the switch.”
This is known as the leucine threshold, typically 2–3 grams per meal, which often equates to 25–35 grams of high-quality protein (Goldman et al., 2024)2.
Without hitting this threshold, your meal may not stimulate MPS effectively—even if you ate protein.
This is why many people eat “some protein,” yet don’t see results in muscle, strength, or metabolism.
DIAAS vs. PDCAAS: Why Protein Quality
Not all protein sources are equal.
Some are more bioavailable, meaning your body digests and absorbs their amino acids more efficiently.
Two major scoring systems exist:
PDCAAS (Protein Digestibility-Corrected Amino Acid Score)
This was the standard for years, but it caps scores at 1.0, which hides meaningful differences between protein sources (FAO, 2013)3.
DIAAS (Digestible Indispensable Amino Acid Score)
The newer, more accurate measure.
It evaluates:
- How many essential amino acids a food contains
- How well your gut absorbs them
- How digestible they are at the end of the small intestine
DIAAS reveals what nutrition experts have observed:
Animal proteins generally score higher, and plant proteins can be excellent when combined wisely.
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Protein–Glucose Connection: Why Protein Stabilizes Blood Sugar
Protein slows digestion and helps regulate glucose by:
- Reducing post-meal blood sugar spikes
- Increasing satiety hormones
- Supporting gluconeogenesis (the creation of glucose from amino acids) when needed
This is why higher-protein meals often reduce cravings and energy crashes (Gannon et al., 2003)4.
Optimizing protein intake is one of the simplest Tweaksly-approved strategies for metabolic stability.
Protein Bioavailability Comparison Table
Below is a simplified table of five common protein sources, comparing grams of protein, leucine content, and bioavailability (via DIAAS or equivalent measure).
|
Protein Source |
Protein (per 100g) |
Leucine (g) |
Bioavailability Score (DIAAS/Estimate) |
|
Whey Protein Isolate |
~90g |
~10g |
1.10–1.25 |
|
Chicken Breast |
~31g |
~2.6g |
1.08 |
|
Eggs |
~13g |
~1.1g |
1.13 |
|
Lentils (cooked) |
~9g |
~0.7g |
0.60–0.70 |
|
Tofu |
~17g |
~1.5g |
0.90 |
How Much Protein Do I Actually Need per Day?
General guidelines suggest:
- 0.8 g/kg bodyweight (minimum for survival, not optimal)
- 1.2–1.6 g/kg for adults seeking healthy aging and maintenance
- 1.6–2.2 g/kg for muscle building, fat loss, or active individuals
Needs increase with age due to anabolic resistance (Schoenfeld & Aragon, 2018)5, making protein a critical focus for older adults.
Can the Body Store Excess Protein? (Amino Acid Pool Explained)
Your body doesn’t “store” protein like fat. Instead, amino acids circulate in a small, dynamic amino acid pool—used for:
- Tissue repair
- Hormone production
- Enzyme creation
Excess beyond immediate needs is converted into energy or stored as fat. This is why consistent protein intake across meals is key.
What Happens If I Don’t Eat Enough Protein?
Inadequate protein may lead to:
- Muscle loss
- Weakened immunity
- Poor wound healing
- Brittle hair and nails
- Persistent hunger
- Lower metabolic rate
- Increased injury risk
Chronic deficiency can accelerate sarcopenia—age-related muscle wasting.
Tweaksly Tip: The 30g Breakfast Tweak
Start your day with 30 grams of high-quality protein.
This helps you hit the leucine threshold, stabilizes blood sugar, and prevents mid-morning cravings.
FAQs
Foods like eggs, poultry, fish, whey protein, Greek yogurt, tofu, lentils, and beans are among the highest—though bioavailability differs.
Most adults thrive on 1.2–1.6 g/kg of bodyweight daily, with higher needs for active or aging individuals.
Fatigue, muscle loss, poor recovery, brittle nails, hair thinning, and cravings.
Low intake, illness, chronic stress, high training volume, aging, or poor digestion.
Your body benefits from protein doses every 3-5 hours, not constant grazing. MPS needs time to rise and fall.
Conclusion: Protein Is the Tweak That Changes Everything
Protein isn’t just a nutrient. It’s a biological requirement, the backbone of healthy aging, metabolic stability, muscle strength, and cellular repair.
By making protein your foundational tweak, you support every major system in your body—one small adjustment at a time.
Disclaimer: This content is for informational purposes only and should not be considered medical advice. Always consult a qualified healthcare provider before making dietary changes.
About the Author
Jalaine McCaskill, founder of Tweaksly, offers practical, research-based nutrition tips and reviews to make healthy eating simple and achievable. Dedicated to distilling complex clinical studies into actionable daily tweaks.
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References:
- Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002. The Shape and Structure of Proteins. Available from: https://www.ncbi.nlm.nih.gov/books/NBK26830/
- Goldman, D. M., Warbeck, C. B., & Karlsen, M. C. (2024). Protein and Leucine Requirements for Maximal Muscular Development and Athletic Performance Are Achieved with Completely Plant-Based Diets Modeled to Meet Energy Needs in Adult Male Rugby Players. Sports (Basel, Switzerland), 12(7), 186. https://doi.org/10.3390/sports12070186
- Food and Agriculture Organization of the United Nations (FAO). (2013). Dietary protein quality evaluation in human nutrition: Report of an FAO Expert Consultation. https://www.fao.org/3/i3124e/i3124e.pdf
- Gannon, M. C., Nuttall, F. Q., Saeed, A., Jordan, K., & Hoover, H. (2003). An increase in dietary protein improves the blood glucose response in persons with type 2 diabetes. The American journal of clinical nutrition, 78(4), 734–741. https://doi.org/10.1093/ajcn/78.4.734
- Schoenfeld, B. J., & Aragon, A. A. (2018). How much protein can the body use in a single meal for muscle-building? Implications for daily protein distribution. Journal of the International Society of Sports Nutrition, 15, 10. https://doi.org/10.1186/s12970-018-0215-1