Does building muscles or getting fat make you dumber? One indicator of intelligence is the brain-to-body mass ratio. An animal is smarter the bigger their brain is compared to their body. Whales have bigger brains than us humans, but they also have much bigger bodies which lowers their brain-to-body ratio. But what if a human dubbles their body weight either trough muscle building or getting fat? The brain does not become twice as big, but it must accommodate for a much bigger body. Does that mean you become more stupid if you work out or eat junk?