Essential vs Non-essential · the line is drawn on rates

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Glycine
The line for "conditionally essential" is drawn on rates, not on the molecule. Meléndez-Hevia 2009 added up an adult's daily glycine use item by item, compared it with the output of the synthesis pathway from serine, and found that production cannot keep up with use. This is a calculated inference that has not been tested against health outcomes in people.

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Essential depends on rates

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Whether a nutrient counts as essential is not decided by the molecule. It is decided by two rates: how fast your body makes it, and how fast your body uses it. When making falls behind using, it has to come from food.

Textbooks split the amino acids into two columns, essential and non-essential, which makes essentiality look like something stamped on the molecule. Yet when the US Institute of Medicine (IOM) defined conditionally essential in 2005, every word was about rates: when the body's own synthesis cannot meet metabolic need, the amino acid needs a dietary source.

Both rates move. An enzyme that is naturally sluggish, not yet developed, or broken by a mutation drags the making side down; a body that is growing, healing a wound, or inflamed pushes the using side up. The same molecule then slides from non-essential into essential. So when you see the word essential, ask first: for whom, and in what state?

Educational content, not medical advice — consult a clinician.

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Essential vs Non-essential · the line is drawn on rates

Story

Connected to · 1

cofactor · 1

Glycine
The line for "conditionally essential" is drawn on rates, not on the molecule. Meléndez-Hevia 2009 added up an adult's daily glycine use item by item, compared it with the output of the synthesis pathway from serine, and found that production cannot keep up with use. This is a calculated inference that has not been tested against health outcomes in people.

Read full story

Stop 1/6

Essential depends on rates

EVIDENCEGUIDE 1 · REVIEW 1

READ THE ORIGINAL

Whether a nutrient counts as essential is not decided by the molecule. It is decided by two rates: how fast your body makes it, and how fast your body uses it. When making falls behind using, it has to come from food.

Textbooks split the amino acids into two columns, essential and non-essential, which makes essentiality look like something stamped on the molecule. Yet when the US Institute of Medicine (IOM) defined conditionally essential in 2005, every word was about rates: when the body's own synthesis cannot meet metabolic need, the amino acid needs a dietary source.

Both rates move. An enzyme that is naturally sluggish, not yet developed, or broken by a mutation drags the making side down; a body that is growing, healing a wound, or inflamed pushes the using side up. The same molecule then slides from non-essential into essential. So when you see the word essential, ask first: for whom, and in what state?

Educational content, not medical advice — consult a clinician.