We investigated with LC-MS techniques, measuring approximately 109 lipid compounds, in mouse brain and liver tissue after 48 hours of starvation and a High-Fat Diet if brain and liver lipid composition changed. We measured Cholesterolesters (ChE), Lysophosphatidyl-cholines (LPC), Phosphatidylcholine (PC), Sphingomyelin (SPM) and Triacylglycerols (TG's) for liver tissue while for brain tissue we had an extra lipid compound the Plasmalogens. In addition, dynamics of hepatic steatosis were determined in an in vivo mouse model with localized non-invasive Magnetic Resonance Spectroscopy (1H-MRS) techniques. In the experimental design Male C57bl6 mice (age 8-12 weeks) were exposed to three treatments: A: They were fed a chow Diet for a period of approximately 40 days (Control group); B: They were fed a High-Fat Diet, containing 0.25% cholesterol (Ch) and 24% energy from bovine lard for a period of approximately 40 days, C: Or they were exposed to 48 hours of starvation. For whole brain tissue of these mice groups the LC-MS techniques indicated that the brain was rather invulnerable to Dietary intervention. The (phospho-) lipid-composition of the brain was unchanged in the starvation group but the cholesterol-ester content was significantly increased in the high High-Fat Diet group. These observations suggest that the brain lipid composition is insensitive to starvation but can be affected by a high High-Fat Diet. In contrast, for liver tissue both 24 h starvation and the 40 day High-Fat Diet resulted in exponential hepatic fat accumulation, although their time course (measured with 1H MRS) techniques was distinctly different. Mass spectrometry (LC-MS) demonstrated for liver tissue remarkable differences in lipid profiles between treatments. 1H-MRS proved to be a reliable method for frequent, repetitive determination of hepatic fat in vivo and a noninvasive alternative to biopsy. Moreover, LC-MS and Principal Component Analysis (PCA) demonstrated that in liver tissue different lipid end products are formed as result of Dietary composition Apparently, for liver tissue starvation and a High-Fat Diet result in a process called hepatic steatosis which is regulated under both conditions via different metabolic pathways. In addition, 1H-MRS techniques demonstrated for liver that the relative amount of unsaturated bindings is significantly higher in the High-Fat Diet group (P≤0.001), which can be deducted from the relative intensities of the (CH=CH) elements and their conjugated unsaturated elements (C-CCH2C=C). We conclude, comparing brain vs. liver tissue that both tissues have a totally different metabolic response to both treatments. The brain is insensitive to starvation but can be affected by a High-Fat Diet while in liver tissue both treatments result paradoxically in a hepatic steatosis. However, for the liver, the dynamics and the lipid profiles of this process of this hepatic steatosis under starvation or a High-Fat Diet are totally different. © 2010 Nova Science Publishers, Inc. All rights reserved.