I'm wary of this early result. If the mice were defecating equal calories yet some were putting on weight and others weren't then the energy had to go somewher

I'm wary of this early result. If the mice were defecating equal calories yet some were putting on weight and others weren't then the energy had to go somewhere. Until there's a clear idea of where that energy went, this result is little more than speculation. In contrast there was another study earlier this year that showed "naturally thin" people simply eat less. There are genetic predispositions in play here. The gut biome too may play a role. The biggest factor however is our relationship with food. People eat for a variety of reasons eg for the experience, to self-medicate (eg anxiety, depression), as a reward, as an activity that itself acts as a reward, etc. The healthiest attitude to have is to treat food as fuel. I tend to eat the same thing a lot. Part of this is decision fatigue. Part of it is probably ADHD or something adjacent. But a lot of it is simply thinking of food as fuel and not tying it to emotional states, social obligations or hobbies.