A vacuum-ultraviolet (VUV) spectroscopy system is proposed for measurement of acetone in human breath that has been attracting attention as a biomarker of body fat metabolism and diagnosis of diabetes. A strong absorption peak of acetone at 195 nm is detected by using a simple system consisting of a deuterium lamp source, a hollow-core fiber gas cell, and a fiber-coupled compact spectrometer corresponding the VUV region. The hollow-core fiber functions as a long path and extremely small volume gas cell and enables sensitive measurement of trace components in exhaled breath. For breath analysis, we applied multiple regression analysis using absorption spectra of O2, H2O, and the acetone standard gas as explanatory variables to quantitate the concentration of acetone in breath. We applied standard addition method based on human breath and as a result, it was found that the measurement accuracy was 0.074 ppm in standard deviation (SD) for healthy human breath with the acetone concentration of around 0.8 ppm and precision was 0.026 ppm SD. We also tried to monitor body fat burn based on breath acetone and confirmed that breath acetone increased after exercises because acetone is a volatile byproduct of lipolysis.