Julia Dowsett, who was hired six months ago as a school meals nutritionist for Enfield council, walks around schools at lunchtime.
"I've seen a child eating a plate of cold chips; another whose lunch box contained three bags of crisps; one whose lunch included two pork pies, a jam sandwich and (again) a bag of crisps," she said.
"You see these things and it's quite concerning."
Miss Dowsett is working through all 80 primary schools in the north London borough, running classes for parents on how to make a variety of healthy packed lunches for their children.
"I think the skill of making a packed lunch has been largely lost. A lot of people don't realise it can be cheaper and easier to make a good, balanced packed lunch than to buy convenience foods off the supermarket shelf," she said.
In response to parents' complaints that their children will not even look at some vegetables, such as spinach, Miss Dowsett brandishes research showing that if you can get them to taste a food 15 times, they will accept it.
Julia MacGechan, who makes packed lunches for three of her four children, has attended one of Miss Dowsett's classes. She admitted that some of the food she had put in her children's lunches in the past, particularly off-the-shelf snacks, had been "awful".
It had been a blow when Eversley primary school, where her two youngest sons go, banned chocolate from lunch boxes. But she now gives her sweet-toothed son Adam a piece of cake instead.
"You get the hang of it. Packed lunches are pretty quick," she said.