I am 58, on a (mostly) strict ketogenic diet since 2013. It has worked wonders for me and I expect to eat this way the rest of my life. I eat a lot of meat and eggs as I have found that combination (1) is something I enjoy very much, and (2) makes me feel the best. I didn’t have much weight to lose but I went from 175 to 160 (high school weight) and under 15% body fat. My energy level is consistently very good. Diet…
Weight loss comes from having a calorie deficit, not from keto. You can gain weight on keto if you eat more calories. You can achieve the same weight loss by just eating fewer total calories, without cutting carbs as well.
Consider: healthy people who are injected a small dose of insulin experience tiredness (reduced energy use) and increased hunger.
Contrary to eating fats, eating carbs triggers the release of insulin. Young, healthy people who have a properly working endocrine system handle eating carbs fine. But for those who don't, it's a different story. Just like those test subjects, their body limits energy consumption and experiences constant hunger.
So yeah, they don't burn enough calories and eat too much of them, but the saying so is pointless if not insulting; the question that needs addressing is why.