Digestion

The common phrase “you are what you eat” is imprecise. A more accurate statement is: your body is what you digest and absorb. Nutrient intake alone is insufficient; physiological benefit depends on effective breakdown, absorption, and utilisation.

In a previous discussion, I noted that protein requirements increase with age. Current research suggests that from approximately 30 years of age onward, protein needs may rise by 1–1.5% per year. One plausible contributor is the gradual decline in digestive efficiency associated with aging.

Mastication

Chewing is not trivial. It is the first mechanical step in digestion and has measurable physiological consequences. Smaller food particle size improves enzymatic access and has been shown to enhance protein digestion.

As a practical benchmark, aim for approximately 50 chews per mouthful. Most individuals fall well short of this. Developing deliberate mastication habits can meaningfully improve digestive efficiency.

This becomes increasingly relevant with age. Bite force begins to decline in the late 20s, meaning greater effort and more thorough chewing are required to achieve the same degree of mechanical breakdown.

Additionally, vigorous mastication during childhood plays a structural as well as digestive role. Consistent chewing stimulus supports appropriate development of the masticatory musculature and promotes adaptive bone growth of both the maxilla and mandible.

This mechanical loading contributes to broader dental arches, improved tongue space, and more optimal nasal airway development. Inadequate chewing stimulus during critical growth periods may, conversely, be associated with narrower arches and reduced airway dimensions.

Gastric Function

Although there may be a modest age-related delay in gastric emptying, evidence suggests that basal gastric acid production remains largely preserved in healthy individuals. This is clinically important, as gastric acid is required to convert pepsinogen into pepsin — the primary enzyme responsible for initiating protein digestion.

However, this does not apply to individuals taking acid-suppressing medications. Approximately 10–20% of Western populations experience reflux, and around 15% of Australians use reflux medication. Acid suppression alters protein digestion physiology and warrants separate consideration.

Pancreatic Enzymes and Small Intestinal Activation

Pancreatic enzyme production appears to decline gradually from around 30 years of age. Several pancreatic proteases are central to protein digestion. In addition, many of these enzymes are secreted in inactive forms and require activation within the small intestine to function effectively.

Emerging research indicates that aging is associated with reduced digestion, absorption, and bioavailability of several amino acids. This suggests that even with adequate intake, net protein utilisation may decline.

Clinical Implications

These digestive changes appear to parallel age-related muscle loss. In individuals not actively engaging in resistance training or other muscle-preserving strategies, skeletal muscle mass declines at approximately 1% per year from the age of 30 onward. Notably, this rate mirrors estimates of declining protein digestive efficiency.

While correlation does not establish causation, the association is biologically plausible. Reduced protein digestion and amino acid availability may contribute to impaired muscle protein synthesis over time.

This has direct implications for aging well. Protein intake alone is insufficient; digestive efficiency must also be considered.

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