I used to have a sausage roll or pastie every morning from the canteen, then almost every day for five years I had a chip butty with gravy and a sausage in batter for dinner
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My parents are decent people and we always had more money than most in my area but my mother didn't cook, my father has no interest in food, he hardly eats.
My mother had the usual excuse, tired after work etc. I got used to just eating toast, crisps, rolls and sandwiches at home. Nearly every Sat my old man would take us to the chippie and then on Sunday we would have fish fingers and chips or summat
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Water was for washing, not drinking. I survived on Coke.
I was fat but in no way did the food affect me mentally, I was pretty bright and finished well ranked in my year (top class and top sets). I did not suffer from sugar highs and lows nor did I do anything no normal teenage kid doesn't. My sister had the same diet and got 10 A*'s and had the best results of anyone in her year.
The only downside I see for myself personally of such a bad diet is that I have a stunted palate now. I don't find most very heathly stuff nice to taste or look at. My GF is Chinese and they eat a ton of greens, I don't see the attraction nor do I like to eat most of it (ps. they do not eat anything like what they sell!!!!)
Kids do need more healthy stuff but I think taking choice away is a bad thing, forcing little people to eat things just because we deem them healthy is just bad. If they want to go home for lunch or eat crisps then let them, the parents need to tackle it.