Background Animal and vegetable-based proteins differ on their effect on many health outcomes, but their relationship with unhealthy aging is uncertain. Thus, we examined the association between changes in animal and vegetable protein intake and unhealthy aging in older adults. Methods Data came from 1951 individuals aged ≥60 years recruited in the Seniors-ENRICA cohort in 2008-2010 (wave 0) and followed-up in 2012 (wave 1), 2015 (wave 2), and 2017 (wave 3). Dietary protein intake was measured with a validated diet history at waves 0 and 1, and unhealthy aging was measured with a 52-item health deficit accumulation index at each wave. Results Compared with participants with a >2% decrease in energy intake from vegetable protein from wave 0 to wave 1, those with a >2% increase showed less deficit accumulation over 3.2 years (multivariable β [95% confidence interval (CI)]: -1.05 [-2.03, -0.06]), 6 years (-1.28 [-2.51, -0.03]), and 8.2 years of follow-up (-1.68 [-3.27, -0.09]). No associations were found for animal protein. Less deficit accumulation over 8.2 years was observed when substituting 1% of energy from vegetable protein for an equal amount of carbohydrate or fat (-0.50 [-0.93, -0.07]), animal protein (-0.44 [-0.81, -0.07]), dairy protein (-0.51 [-0.91, -0.12]), or meat protein (-0.44 [-0.84, -0.04]). Conclusions Increasing dietary intake of vegetable protein may delay unhealthy aging when replacing carbohydrates, fats, or animal protein, especially from meat and dairy.