Jet lag, a varying set of symptoms affecting performance and judgment in people who fly long distances, may have serious consequences for military personnel and operations. Diet is postulated as one low-cost, safe, and easily altered factor that may modify jet lag. Incidence and patterns of jet lag were evaluated, as well as an intervention with the Argonne diet, which alternates moderate feasting and fasting 4 days before departure, in 186 National Guard personnel deployed across nine time zones. As volunteers, 95 used the diet in preparation for deployment and 39 used it in preparation for return. Jet lag was significantly more frequent on either deployment or return or both for nondieters. Sedentary civilian jobs and a previous history of jet lag were associated with jet lag in this study.