We get yet another reminder that the Pattersons are low class people who eat crap and won't moderate their appetites.
Panel 1: It would seem that Elly is displeased with what Mike spent his allowance on: bubble gum and what I assume is a chocolate bar. That's because her eyes are all bugged out when she says "Michael...you spent that whole dollar on junk!"
Panel 2: Being told that he's doing something wrong has the predicted result: anguished denial. He clasps the empty calories to himself and whines "Junk? You can't call this junk... it's good stuff!"
Panel 3: He then adds volume to his moaning as he squeals "Kids need candy! It's food energy....they said so on TV."
Panel 4: Instead of cutting off his allowance, sending him to his room for backchat or even getting him to wash his chocolate-smeared face and change out of the chocolate-stained T shirt he's wearing, Elly sends him on his way and, with a defeated expression on her face, thought-bubbles "How can you argue with the Gospel according to TV?"
Summary: My answer is "Very easily"; as babsbybend said, Elly's next move should be to deny him TV privileges, reduce his allowance and start serving real food that isn't drowning in sauce or syrup so he knows eating healthy doesn't mean sacrificing taste. Sadly for us, she isn't strong enough to argue; watching her cave after being bullshitted sort of tells me why she found him a handful: she has no spine and therefore should not be in a position to enable children's bad habits.