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Quantitative evolutionary design of nutrient processing: glucose.

Anthony C Steyermark¹, Mandy M Lam, Jared Diamond

¹Department of Physiology, University of California School of Medicine, Los Angeles, CA 90095-1751, USA. acsteyermark@stthomas.edu

Proceedings of the National Academy of Sciences of the United States of America

|June 22, 2002

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Rats can process glucose at rates 2.2 times their normal intake, demonstrating a significant safety factor in nutrient processing. This excess capacity may have evolved to handle varied nutrient loads and metabolic demands.

Area of Science:

Physiology
Evolutionary Biology
Metabolic Science

Background:

Quantitative evolutionary design examines biological capacities relative to natural nutrient loads.
Understanding nutrient processing by the intestine and associated organs is crucial for metabolic health.

Purpose of the Study:

To investigate the relationship between nutrient-processing capacities and natural nutrient loads.
To experimentally determine the limits of glucose processing beyond the intestine using total parenteral nutrition (TPN).

Main Methods:

Administered nutrients intravenously to rats via total parenteral nutrition (TPN) to control nutrient delivery rates.
Compared glucose processing in control rats (oral TPN) versus experimental rats (intravenous TPN).
Monitored glucose levels in serum and urine, serum osmolality, weight gain, and survival rates.

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Main Results:

Rats processed oral TPN glucose at 42 mmol/day completely.
Rats processed infused TPN glucose up to 92 mmol/day completely.
Higher infusion rates led to impaired glucose processing, hyperglycemia, increased serum osmolality, diuresis, dehydration, reduced weight gain, and decreased survival, mimicking nonketotic hypertonicity.

Conclusions:

Rats possess a glucose processing safety factor of 2.2, indicating a capacity significantly exceeding voluntary intake.
This excess capacity likely evolved to manage diverse nutrient loads, increased demands, or rapid glucose mobilization.
The findings provide insights into metabolic limits and evolutionary adaptations for nutrient processing.