Introduction: Neuropeptide Y (NPY) signaling in the brain plays an important role in energy regulation, and is altered during diet-induced obesity. Yet, NPY function during the consumption of specific diet components remains to be fully determined. We have previously demonstrated that consumption of a saturated fat component (free-choice high-fat; fcHF), a sucrose solution (high-sugar; fcHS), or both (fcHFHS) combined with a standard diet (chow and water) has diverse effects on Npy expression in the arcuate nucleus and the sensitivity to intraventricular NPY administration. Arcuate NPY neurons project to the lateral hypothalamus (LHA), and NPY administration in the LHA potently promotes chow intake in rats on a standard diet. However, it is currently unclear if short-term consumption of a palatable free-choice diet alters NPY function in the LHA. Therefore, we assessed the effects of intra-LHA NPY administration on intake in rats following one-week consumption of a fcHF, fcHS, or fcHFHS diet. Methods: Male Wistar rats consumed a fcHF, fcHS, fcHFHS, or control (CHOW) diet for one week before NPY (0.3 μg / 0.3 μL) or phosphate-buffered saline (0.3 μL) was administered into the LHA. Intake was measured 2h later. fcHFHS-fed rats were divided into high-fat (fcHFHS-hf) and low-fat (fcHFHS-lf) groups based on differences in basal fat intake. Results: Intra-LHA NPY administration increased chow intake in fcHFHS- (irrespective of basal fat intake), fcHF- and CHOW-fed rats. Intra-LHA NPY infusion increased fat intake in fcHF-, fcHFHS-hf, but not fcHFHS-lf, rats. Intra-LHA NPY infusion did not increase caloric intake in fcHS-fed rats. Discussion: Our data demonstrate that the effects of intra-LHA NPY on caloric intake differ depending on the consumption of a fat or sugar component, or both, in a free-choice diet. Our data also indicate that baseline preference for the fat diet component modulates the effects of intra-LHA NPY in fcHFHS-fed rats.