Transcription factor forkhead box O1 (FoxO1) regulates energy expenditure (EE), food intake, and hepatic glucose production. These activities have been mapped to specific hypothalamic neuronal populations using cell type-specific knockout experiments in mice. To parse out the integrated output of FoxO1-dependent transcription from different neuronal populations and multiple hypothalamic regions, we used transgenic mice expressing Cre recombinase from the Nkx2.1 promoter to ablate loxP-flanked Foxo1 alleles from a majority of hypothalamic neurons (Foxo1KO(Nkx2.1) mice). This strategy resulted in the expected inhibition of FoxO1 expression, but only produced a transient reduction of body weight as well as a decreased body length. The transient decrease of body weight in male mice was accompanied by decreased fat mass. Male Foxo1KO(Nkx2.1) mice show food intake similar to that in wild-type controls, and, although female knockout mice eat less, they do so in proportion to a reduced body size. EE is unaffected in Foxo1KO(Nkx2.1) mice, although small increases in body temperature are present. Unlike other neuron-specific Foxo1 knockout mice, Foxo1KO(Nkx2.1) mice are not protected from diet-induced obesity. These studies indicate that, unlike the metabolic effects of highly restricted neuronal subsets (proopiomelanocortin, neuropeptide Y/agouti-related peptide, and steroidogenic factor 1), those of neurons derived from the Nkx2.1 lineage either occur in a FoxO1-independent fashion or are compensated for through developmental plasticity.