Jeb Bush has adopted a drastic weight-loss program on the presidential campaign trail, as he prepares to challenge mostly younger and leaner field of Republican rivals.

The former Florida governor is melting away pounds at a staggering rate, but has led to regular bouts of dietary crankiness, The New York Times reports.

The months-long experiment in deprivation — little to no starch, dairy, or refined sugar, in adherence to the Paleo “caveman” diet — is his latest in a long struggle with weight gain for Bush.

Unlike a mountain-biking brother and trim elderly father, Bush has tried everything from climbing 22 flights of stairs a day to joining the low-carb Atkins craze of the early 2000s, The Times reports.

By embracing the Paleo diet, Bush has lost about 30 pounds since December, according to friends and observers.