It's very possible for both to be right in those claims. Modern diets are so profoundly unhealthy that almost any concerted effort to eat better will yield noticeable results.

Undisciplined

I wonder about this. I suspect the absence is why people see improvements. Cutting sugar and carbs is pretty obviously an improvement. 

kepford

Fitness

I have a couple family members who have done the carnivore diet for years and absolutely swear by it. They cite higher energy levels and better overall health. However, I often hear the same thing from vegetarians who reference all the benefits that come from a plant-based diet. Is it possible for both to be right? Does it depend on body-type/genetics?