From the comments at Knuckledragin:

Gasoline contains 20,000 BTUs per pound and ethanol contains 12,800 BTUs per pound. When you buy fuel at the pump, you are buying energy. E 15 contains about 2% less energy than E 10, So your gas mileage will be about 2% less. The Biden administration expects this move to lower gas prices by about $.10 a gallon. So, if gas is $4.00 per gallon, 2% of that is 8 cents a gallon, so the real reduction in prove is about 2 cents a gallon. Let’s go Brandon!

Of course the (Unimportant Side Effect) will be third world starvation,  revolutions, and actual hunger in The United States.   And for many budgets, meat will be off the table as animal feed becomes to expensive.