The 30th century of Earth-One had Tenzil Kem of the planet Bismoll-One, a world where all the natives of that planet had to learn to eat any matter due to microbes which made their food stock inedible. This adaptability translated to his ability to both chew and digest matter at the rate of superhuman speed, while having a high metabolism. This led to his inclusion in the Legion of Super-Heroes, although his membership records wasn't consistent due to several mitigating factors. For instance, on one occasion, he ate to much in order to escape a prison camp which led to his becoming obese. Thankfully, the effects were reversed soon afterwards.
In the 20th century of Earth-Two was Theodore "Tubby" Watts, an assistant photo-journalist for Sees-All-Tells-All News, alongside his boss Johnny Chambers. Chambers was secretly the masked man known as Johnny Quick, who obtained a super-speed formula that allowed him to move as fast as the Flash, whom he joined alongside as a member of the All-Star Squadron. On a few occasions, Tubby tagged along with the All-Stars, and especially during several of Quick's solo missions. On at least one occasion, Tubby used the formula 3x2(9yz)4a to grant himself superhuman speed, although his large physique didn't handle it quite well, and so he retired from superheroics.
Back to Kem, whose career as Matter-Eater Lad had hit several roadblocks, not least of which was his eating the "Miracle Machine" in order to save the universe from its destructive power. He got better, although he eventually returned to his native world to become a politician. Meanwhile, Tubby stayed surprisingly young... perhaps a side effect of the speed formula... and remained by Johnny's side reporting on news across America decades later.