We have 8 billion people. We have enough people to solve both the energy problem and the food efficiency problem.
That said, it's very, very funny that you responded to an article about energy inefficiency (calorie -> calorie) and said we should solve our energy problems. Beef is an energy problem! We're putting 30x the energy into the product against the energy we get out! Thats wasted energy!
Eh. Grow beef mostly grazed on marginal land that can't support other agriculture.
This is how a LOT of beef is produced and how most of it SHOULD BE.
They're not "lost calories" if they're produced on large swaths of semi-arid land that don't support any other kind of agriculture.
And on the opposite side... a LOT of those "lost calories" are corn. Corn is substantially more productive than other crops and people don't want to replace large portions of their diet with cereal grains or corn syrup so much of those "lost calories" would also be lost to much less efficient crops.