The specific optical spectra of tissues contain information about the biochemical composition. We present a simple optical fiber probe spectrometer design for noninvasive measurement of oxygen saturation in the microvasculature of stomach tissue. In a human Esophagectomy model with 23 patients, we measured the spectrum following surgical ligation of two of the three arterial paths to the stomach tissue that will become the anastamosis. Combining a diffusion model for semi-infinite slab remittance with absorption spectroscopy, we are able to specify the ratio of oxy-hemoglobin to deoxy-hemoglobin present in the tissue. We show a resting state of 0.47 (oxy-hemaglobin/total-hemaglobin) saturation decrease of 29% (p < 0.01) when arterial supply is reduced by artery ligation.