Why braking hard will cause gas wasted?

"The Environmental Protection Agency estimates that accelerating rapidly and braking hard can reduce your car's fuel efficiency by as much as five percent."

Accelerating rapidly will cost a lot of gas, that makes sense, but how does braking hard cause the same effect on gas? Shouldn't it be saving gas instead, since there is a cut on gas burning?

It takes a lot of gas to brake hard so thats why it wastes a lot of gas.

hard breaking at a stop light means you have to accelerate again to get back to speed. ALL acceleration uses more gas than maintaining a steady speed. So it's an indirect effect. There may be a slight direct effect as well since hard breaking means your average RPM's prior to breaking will be higher than if you coasted or breaked more slowly but it's likely far less significant than the other reason.

hard breaking at a stop light means you have to accelerate again to get back to speed. ALL acceleration uses more gas than maintaining a steady speed. So it's an indirect effect. There may be a slight direct effect as well since hard breaking means your average RPM's prior to breaking will be higher than if you coasted or breaked more slowly but it's likely far less significant than the other reason.

i think they mean what is the point of speeding up when you're going to brake anyway. i don't think they mean the braking itself contributes to wasting gas. like why speed up to slow down suddenly when you can just look ahead and cruise up the light without stepping more on the gas at all.

hard breaking at a stop light means you have to accelerate again to get back to speed. ALL acceleration uses more gas than maintaining a steady speed. So it's an indirect effect. There may be a slight direct effect as well since hard breaking means your average RPM's prior to breaking will be higher than if you coasted or breaked more slowly but it's likely far less significant than the other reason.