Вы можете использовать следующий код
library(sjPlot)
library(ggplot2)
mod <- glm(mpg ~ wt, data = mtcars)
set_theme(base = theme_classic(), #To remove the background color and the grids
theme.font = 'serif', #To change the font type
axis.title.size = 1.5, #To change axis title size
axis.textsize.x = 1.2, #To change x axis text size
axis.textsize.y = 1.2) #To change y axis text size
plot_model(mod, type="pred", show.p = TRUE, axis.title = c("Cicatríz umbilical",expression(paste(delta^{13}, "C(‰)"))), title = "")
![enter image description here](https://i.stack.imgur.com/QvxF0.png)