"Calorie content" is not just something in a substance, calories are energy, not a substance. That is, look, you eat a certain amount of some kind of food that is digested and partially absorbed by your body in an already altered form (decomposed into simple elements - amino acids, fats, proteins) and these elements can potentially give in the process of chemical processing by the body and decomposition into even simpler components release energy.
The most energy-intensive nutrient (what we can eat and absorb) is fat. One gram of fat will release 9 calories.
So you can't eat anything like that.
What kind of substance? If only uranium)))))) In this case, weight gain is a problem that will worry you in the last place, I dare to assure you))))) So - do not worry, eat uranium, get fat do not have time))))