There’s that professor who ate only McDonald’s, but added a daily walk to his routine. He lost weight.

https://www.al.com/entertainment/2015/08/meet_the_science_te...

Caveat: Losing weight is not necessarily the same as being healthier in this case

As for potatoes – I love using them as the carb in lunch. High volume, low calories, great combo. Makes you feel full but isn’t actually that much food. As a small person it’s easy to overeat in America so gotta be careful.