Protein is important for maintaining muscle mass, strength, metabolic health and physical function as we age.
However, when it comes to supporting muscle growth, recovery and body composition, the amount of protein you eat is only part of the equation.
What Are Amino Acids?
Nutritional protein is made up of smaller compounds called amino acids.
There are 20 amino acids that the body uses to build and repair tissues, produce enzymes and hormones, support immune function, and maintain healthy skin, hair and nails.
Of these 20 amino acids, 9 are classified as essential amino acids. These are amino acids that the body cannot produce on its own and must therefore be obtained through food.
The essential amino acids are:
- Histidine
- Isoleucine
- Leucine
- Lysine
- Methionine
- Phenylalanine
- Threonine
- Tryptophan
- Valine
While all amino acids have important functions within the body, the essential amino acids are particularly important for supporting muscle repair, recovery and growth.
Why Amino Acid Composition Matters
If one or more essential amino acids are lacking from a protein source, muscle protein synthesis (the process by which the body repairs, maintains and builds muscle tissue) is limited, even when total protein intake appears adequate.
This is because the body can’t manufacture the missing essential amino acid/s and therefore cannot fully utilise the other amino acids available.
In addition, different protein sources contain varying amounts of each essential amino acid. Some proteins are particularly rich in amino acids that play a key role in muscle protein synthesis, while others contain lower concentrations.
As a result, two protein sources may provide the same number of grams of protein, but differ in their ability to support muscle repair, recovery and growth.
Not all protein sources are equally effective at stimulating muscle protein synthesis.
A “complete” protein contains all 9 essential amino acids in sufficient amounts to support muscle protein synthesis.
- Most animal-derived proteins are complete proteins and generally have higher digestibility than many plant-based protein sources.
- Most plant proteins contain all or some of the essential amino acids, but are generally lower in one or more essential amino acids than animal-derived protein sources.
This doesn’t mean plant proteins are ineffective. However, a greater variety is often needed to obtain all essential amino acids in adequate amounts.
Leucine: The Key Amino Acid for Muscle Growth
Leucine is an essential amino acid that acts as a key signal that initiates muscle protein synthesis.
Without sufficient leucine, the muscle protein synthesis response is reduced, even if total protein intake is adequate.
Protein sources naturally rich in leucine include:
- Whey protein
- Lean meat
- Chicken
- Fish
- Eggs
- Dairy products
Whey protein is considered the most effective protein supplement for stimulating muscle protein synthesis due to its high leucine content and rapid digestibility.
While whole foods should always form the foundation of your nutrition, a whey protein supplement can be a convenient way to increase your protein intake and support recovery after training.
The Importance of Protein After 40
As women move through perimenopause and menopause, declining estrogen levels can contribute to:
- Reduced muscle mass
- Lower strength levels
- Slower recovery from exercise
- Increased fat accumulation (you can read more about that in my article “Perimenopause Belly Fat“)
- Reduced insulin sensitivity (you can read more about that in my article “Perimenopause & Insulin Sensitivity“)
At the same time, the body’s response to dietary protein becomes less efficient (anabolic resistance).
As we age, our muscles require a greater protein stimulus to grow and repair.
This is one reason protein intake becomes increasingly important after 40, particularly when combined with regular strength training.
It’s not simply about preventing muscle loss. Maintaining muscle mass supports:
- Metabolic health
- Physical function
- Balance
- Independence
- Glucose regulation
- Long-term quality of life.
Why Protein Source Matters
Different protein sources contain different amino acid profiles, vary in digestibility, and differ in their ability to stimulate muscle protein synthesis.
For women over 40, particularly during perimenopause and menopause, prioritising protein sources rich in essential amino acids and leucine may help support muscle mass, strength, recovery and metabolic health.
Protein isn’t just about hitting a daily target.
It’s about choosing protein sources that provide the amino acids needed to support muscle protein synthesis, recovery and healthy ageing.
Knowing which protein to eat is important.
Knowing how much to eat, when to eat it, and how to combine it with effective training is even more important.
That’s exactly what we focus on inside my 4 Week Starter Challenge – A science-based program designed specifically for women over 40.
Results from following a science-based plan designed specifically for women over 40.