Glucose restriction is very effective in C. elegans. In mammals, neither IF nor glucose restriction (i.e. low-carb) is conclusive with regards to longevity. The most prominent effect is on overall health. And here, low-carb works best.

OK, so the premise is some form of restriction to increase lifespan. In a mechanical sense, this makes sense. The less often we use a machine (or the less stress for a continuously running machine), the longer it remains functional. In a biological sense, it doesn't. To wit, chaperone-mediate autophagy, whereby an energy substrate - ketones - stimulate clean-up of what would otherwise decrease lifespan. The more ketones, the less crud, the longer lifespan. Or at least, if lifespan was a function of crud. It's not. Health is a function of crud.

OK, so the premise isn't just lifespan, it's up-to-maximum lifespan. What controls maximum lifespan? As far as anybody knows, we don't know. Whatever these experts are looking at ain't it, cuz it's all about health - up-to-maximum lifespan - not about absolute lifespan.