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Int J Obes (Lond). 2014 Sep;38(9):1248-50. doi: 10.1038/ijo.2014.7. Epub 2014 Jan 20.

Breath carbon stable isotope ratios identify changes in energy balance and substrate utilization in humans.

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USDA ARS Human Nutrition Research Center, Grand Forks, ND, USA and University of Wisconsin-Madison, Madison, WI, USA at time of work; Paso del Norte Institute for Healthy Living, El Paso, TX, USA at time of publication.
Department of Animal Sciences, University of Wisconsin-Madison, Madison, WI, USA.
University of North Dakota, Grand Forks, ND, USA.
Department of Nutritional Sciences, University of Wisconsin-Madison, Madison, WI, USA.
Department of Ob/Gyn and Wisconsin National Primate Research Center, University of Wisconsin-Madison, Madison, WI, USA.
Department of Zoology, University of Wisconsin-Madison, Madison, WI, USA.


Rapid detection of shifts in substrate utilization and energy balance would provide a compelling biofeedback tool for individuals attempting weight loss. As a proof of concept, we tested whether the natural abundance of exhaled carbon stable isotope ratios (breath δ(13)C) reflects shifts between negative and positive energy balance. Volunteers (n=5) consumed a 40% energy-restricted diet for 6 days followed by 50% excess on day 7. Breath was sampled immediately before and 1 h and 2 h after breakfast, lunch and dinner. Exhaled breath δ(13)C values were measured by cavity ring-down spectroscopy. Using repeated measures analysis of variance (ANOVA) followed by Dunnett's contrasts, pre-breakfast breath values on days 2-6 were compared with day 1, and postprandial day 7 time points were compared with pre-breakfast day 7. Energy restriction diminished pre-breakfast breath δ(13)C by day 3 (P<0.05). On day 7, increased energy intake was first detected immediately before dinner (-23.8±0.6 vs -21.9±0.7‰, P=0.002 (means±s.d.)), and breath δ(13)C remained elevated at least 2 h post dinner. In conclusion, when shifting between negative and positive energy balance, breath δ(13)C showed anticipated isotopic changes. Although additional research is needed to determine specificity and repeatability, this method may provide a biomarker for marked increases in caloric intake.

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