It is critical to use convincing research methodology to demonstrate the benefits of nutrition assistance programs targeted to vulnerable older adults. We examined the impact of Older Americans Act Nutrition Program (OAANP) participation on food security in participants and waitlisted people in Georgia using two waves of self-administered mail surveys conducted 4 months apart (n = 717, mean age 74.6 ± 9.5, 70.9% female, 33.2% black). At baseline, 54% of the sample was food insecure. Waitlisted people reported higher levels of persistent food insecurity (45.9%) or becoming food insecure (10.0%) than participants (29.3% and 7.1%, respectively) over 4 months. While considering potential confounders, the estimated odds of achieving food security were 1.65 times (95% CI: 1.10–2.48) higher in participants than in waitlisted people over 4 months. Our data suggest the feasibility of using food insecurity measures to detect the benefits of OAANP participation as well as the need to increase the capacity of OAANP.