"Actually all elements are capable of fission.
"

You misunderstand what fission is, the flow of electrons has nothing to do with fission, fission is the splitting of atoms. All elements are capable but only elements heavier than iron produce more energy than they require when their nucleus is split, the decay of radioactive isotopes is something completely different than fission.

The gasoline was an example to show a concept, not to be taken literally as drinking gasoline is ridiculous, it's to show that different kinds of energy can not be used interchangably.

No amount of physiological change would allow you to transform the heat from nuclear reactions into chemical energy wich the body requires.

To recap, the decay of radioactive isotopes is not in fact nuclear fission, the reason it's call nuclear is the nucleus of the atom splits, and only elements lighter than iron produce energy when their nucleus is split.

All of this is only adding on to the fact that even if nuclear reactions could take place in the body, it would take internal steam powered turbines to harness it.

Combustion and fission are absolutely unrelated. Combustion is a chemical reaction in wich an element bonds with oxygen. It happens every day. Rust is in fact slow combustion. Fission is the splitting of an atoms nucleus, no chemical reaction takes place, they aren't on the same scale so one is not an "order of magnitude" above the other

For example, when a hydrocarbon (chains of carbon attached to hydrogen) burns, the oxygen in the air splits up the carbon and hydrogen, forming bonds with both to form carbon dioxide and hidrogen dioxide (water). When a uranium nucleus is split it destroys the uranium atom, splitting it into two or more lighter elements, hence, totally different reactions. It is akin to comparing a physical change (for example cutting an apple) and a chemical change (burning gasoline)

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