Fructose is involved in fat gain, preventing natural weight regulation in animals.

“store fat normally animals will regulate their weight beautifully they just maintain their weight normally if you take an animal and you put a tube down its throat and give it extra food to make it gain weight if you take the tube out the animal will go right back to its normal weight if you starve an animal and so it's below its normal weight and then you let it just eat it will eat back to its regular weight but when it wants to gain fat it will do so usually through a mechanism that involves fructose”