(13)C-Breath testing in animals: theory, applications, and future directions

Area of Science:

• Comparative Physiology
• Biochemistry
• Nutritional Science

Background:

• The carbon isotope composition of exhaled breath reflects oxidized metabolic fuels.
• Stable carbon isotope (13C) breath testing is a minimally invasive in vivo method to study substrate oxidation.
• Its use has surged in comparative physiology due to convenience and affordability.

Purpose of the Study:

• To review the practical aspects of (13C) breath testing.
• To identify strengths and weaknesses of different methodological approaches.
• To highlight applications in human and animal studies.

Main Methods:

• Review of (13C) breath testing methodologies, including natural abundance vs. enriched tracers.
• Comparison of experimental protocols like diet-switching and fuel-switching.
• Discussion of factors in experimental design: extrinsic vs. intrinsic labeling, and modeling nutrient oxidation.

Main Results:

• Case studies demonstrate diverse applications in human physiology and comparative studies.
• The technique is valuable for investigating fuel use, energetics, and carbon turnover across species.
• (13C) breath testing provides insights into thermobiology, locomotion, and nutrition.

Conclusions:

• The review critically compares various (13C) breath testing approaches.
• It emphasizes the technique's utility in answering fundamental questions in physiology and nutrition.
• The authors advocate for increased and rigorous use of (13C) breath testing in research.