I was being sarcastic, I personally don't believe genetics play a role in obesity what so ever. The equation is simple taking In more calories then the body needs leads to fat gain, taking in less calories them the body needs leads to fat loss it's that simple.
Well, I would reword it to "taking In more calories then the body needs leads to weight gain, taking in less calories them the body needs leads to weight loss it's that simple."
I realize you might have meant it that way but yo-yo dieters that starve themselves and trigger the homeostatic mechanisms in the body will actually lose about half muscle mass and half fat mass in their weight loss efforts. Thing is, there are tons fo studies that indicate that within a year, the majority of those individuals gained back all of their fat mass and
added even more to the baseline. Whats worse, unless the individual starts lifting weights, they don't put the muscle mass back on with the rebound weight gain. So basically, when it is all said and done, starvation diets result in a yo-yo effect, which leaves the person with more fat and less muscle mass, lowering the overall BMR and making it even harder to lose weight the next go around.
Caloric deficits tend to lower BMR by eating away at amino acids through gluconeogenesis. Doing this to the extreme - like eating less than your BMR, will trigger homeostatic mechanisms and cause your body to "fight" the weight loss. Of course, macro composition, meal timing, meal size and meal variety play key roles in this too. It's a system that is far more complicated than "calories in, calories out".