Not All Protein is Equal: What Bioavailability Means for Women Over 40

If you're eating plenty of protein but still losing muscle, the problem might not be how MUCH you're eating - it might be WHAT you're eating. Because here's something most women don't know: Not all protein sources are created equal.

The Protein Paradox

You track your protein intake carefully. You hit your daily goal of 80-100 grams. You're doing everything "right."

But your muscles still feel weaker. Your body composition isn't changing. You're wondering what you're missing.

The answer might be simpler than you think: bioavailability.

What the Research Shows

A 2023 study from Purdue University tested this directly. Researchers gave people equivalent two-ounce servings of different proteins:

• Pork (animal protein)
• Eggs (animal protein)
• Black beans (plant protein)
• Almonds (plant protein)

Then they measured how many essential amino acids showed up in people's bloodstreams.

The result? Animal proteins delivered significantly more usable amino acids than plant proteins.

We're talking about a 30-40% difference in how effectively your body can use the protein.

Why This Matters for Women Over 40

Let's say you're eating 80 grams of protein per day.

If that protein is primarily from high-bioavailability sources (animal proteins), your body is using most of it - maybe 70-75 grams worth.

But if that protein is primarily from lower-bioavailability sources (plant proteins), your body might only be using the equivalent of 50-55 grams.

That 20-25 gram difference? That's the difference between maintaining muscle and losing it.

The Math:

Scenario A: High-Bioavailability Protein
80g consumed → ~75g used by body = Muscle maintained

Scenario B: Low-Bioavailability Protein
80g consumed → ~55g used by body = Muscle loss over time

Same amount eaten. Different results.

What Affects Protein Bioavailability?

1. Amino Acid Profile

Animal proteins contain all nine essential amino acids in optimal ratios. Plant proteins often lack one or more, or have them in lower amounts.

2. Digestibility

Animal proteins are easier for your body to break down and absorb. Plant proteins contain fiber and compounds that can interfere with absorption.

3. Leucine Content

Leucine is the "trigger" that tells your muscles to start building. Animal proteins have 2-3 times more leucine than plant proteins.

Protein Bioavailability Rankings

Highest Bioavailability (Your body uses 90-100%):

• Whey protein isolate
• Eggs
• Chicken and turkey
• Fish
• Greek yogurt

High Bioavailability (Your body uses 80-90%):

• Beef
• Pork
• Soy (tofu, tempeh)

Moderate Bioavailability (Your body uses 60-75%):

• Quinoa
• Beans and lentils
• Pea protein

Lower Bioavailability (Your body uses 40-60%):

• Wheat protein
• Rice protein
• Nuts and seeds

Does This Mean Plant Protein is Bad?

Absolutely not.

Plant protein is associated with:

• Healthy aging
• Lower risk of chronic diseases
• Better overall longevity
• Lower inflammation

The research consistently shows benefits from plant protein for overall health.

But when it comes specifically to MUSCLE PRESERVATION - which is critical for women over 40 - animal proteins have a clear advantage.

The answer isn't either/or. It's BOTH.

Practical Strategies

Strategy 1: The 80/20 Approach

Get 80% of your protein from high-bioavailability sources (animal proteins, whey). Get 20% from plant sources for overall health benefits.

Example for 100g daily protein:

• 80g from: eggs, chicken, fish, Greek yogurt, whey protein
• 20g from: beans, nuts, quinoa, whole grains

Strategy 2: For Vegetarians

If you avoid meat but eat dairy and eggs:

• Prioritize eggs, Greek yogurt, cottage cheese, whey protein
• These have the same high bioavailability as meat
• You can meet muscle preservation needs

Strategy 3: For Vegans

If you eat fully plant-based:

• Increase total protein target by 25% (if aiming for 100g, eat 125g)
• Prioritize soy and quinoa (highest plant bioavailability)
• Combine complementary proteins (rice + beans)
• Consider pea/rice protein blend supplements

The Bottom Line

Your protein tracking app doesn't know about bioavailability. It just counts grams.

But your body knows. Your muscles know.

If you're eating enough protein by the numbers but still seeing muscle loss, ask yourself: What SOURCES am I relying on?

The answer to that question might be the missing piece.

Because the protein your body can USE matters more than the protein you eat.

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Sources: Mathai JK, et al. Nutrients. 2023;15(13):2870; PMC6723444; British Journal of Nutrition 2017