Agree, I don't think he's a twit and had good intentions (along with raising his profile as I don't for a second think it was totally selfless).I don't hate him but his approach to what (in my view) was a noble goal was just awful.
But the challenge is so big he needed to dedicate a lot more time to it and have a proper plan.
What he's actually done is when he's had a few weeks spare in his calendar he's started on the school dinners or sugar tax stuff. If he wanted to make a real change he needs to dedicate a lot more time to it. Either do it properly or don't bother.
He was advertising middle class junk food for Sainsbury's while berating others for having junk food that didn't have as fancy names and ingredients.