One of the abiding memories of my childhood is of my mother banging on about the evils of processed foods, E numbers, additives, apples sprayed with chemicals, white plastic bread, intensively farmed meat and so on. This was roughly 30 years ago, and it used to drive me mad.

If I had a friend with terrible teenage skin, my mother would say their diet was obviously a disaster. If a small child was badly behaved, she’d raise a knowing eyebrow and talk about sugar rushes. Mercifully, her tastes were too deluxe to adopt a lentilly, 1970s vegan take on things, but she was the first person I knew to form a deep and meaningful, non-hippie relationship with the health food shop. If I’d had to describe her relationship with diet and nutrition, I’d have said “cranky”, and rolled my eyes, before dreaming of McDonald’s.

Food scares used to irritate me beyond reason. Like everyone, I thought: “If you listened to all this guff, you’d be too scared to eat anything at all.” I liked to reinforce this with “a little of everything does you good”.

Well, we all turn into our mothers in the end. Over the years, I’ve noticed, with some annoyance, that all of mine’s food-related pronouncements were becoming true. Oily fish is incredibly good for you (and makes a child brainier if you eat it while pregnant, according to research published last week). Hydrogenated fats really aren’t a great idea. Sugar does cause bizarre fluctuations in mood and behaviour (to say nothing of weight).

And, despite myself, I’ve now adopted an interest in food and nutrition which my youthful self would have found cripplingly embarrassing. I believe sugar is the devil. I ban fizzy drinks. There hasn’t been white bread in my house for years. Our meat and vegetables are organic. I take a loony amount of supplements. I’m obsessed by fish oils. You know the woman you see in the supermarket, carefully reading all the labels and then ranting to herself about how it’s no wonder everybody’s obese and lethargic and sick? I am she.

I am also the woman who says: “There is no need for anybody to have bad skin or feel tired in the afternoons,” and, more controversially: “That poor child doesn’t have attention deficit hyperactivity disorder, ADHD. He just gets fed crap.” And, yes, my children roll their eyes. And yes, there is a part of me that knows it’s earnest and bourgeois and hideously middle-class to obsess about my family’s food in this way when most of the world is starving and the average British child gets fed filth at school. But I can’t stop. Having lost three stone (and counting) in the process helps, I have to say.

So when I read, as I did last week, that two separate reports claim that changes in diet over the past 50 years appear to be a major factor behind a significant rise in mental illness, I don’t roll my eyes any more, but nod vigorously in agreement. The Mental Health Foundation said last week that studies had clearly linked ADHD, depression, Alzheimer’s and schizophrenia to junk food and the absence of essential fats, vitamins and minerals in diet.

Another report published last week, by Sustain, warned that the cost to the country of mental illness — currently almost £100 billion a year — will continue to rise unless the government focuses on diet in its food, farming, education and environment policies.

“Food can have an immediate and lasting effect on mental health and behaviour because of the way it affects the structure and function of the brain,” the report says. Equally persuasive was an Oxford University study published last May which showed that junk food and highly processed diets cause bad behaviour and learning difficulties in children. It also suggested that ADHD could be “treated” by an improved diet, rather than by medication. This was the study, you may remember, that caused a rush for omega-3 fish oil supplements, after they were found to improve dramatically concentration in children.

What is interesting about all this is that the gist of it is reaching even the people with an in-built resistance to what they see as food faddism. I’m not the only one who has done an about-turn — not when Marks & Spencer has banned hydrogenated fats from its stores, and now uses free-range chicken and eggs in its ready meals, when the shelves of every supermarket are groaning with wheat-free this and sugar-free that, and when even Starbucks offers to make your latte with soya milk.

We have a growing network of farmers’ markets, organic vegetable box schemes, old-fashioned butchers who source their meat responsibly. The people I know whose diets I least admired — takeaways, fizzy drinks, alcohol and chocolate about covers it — are getting in on the act too. They’re no longer chucking their children quite as many bagfuls of sweets and crisps, they’ve reacquainted themselves with vegetables other than the potato, and they no longer look alarmed when you present them with a piece of broccoli.

Food has always been in part about class. If you believe, and it’s hard not to, as Jamie Oliver almost sainted himself in an effort to point out, that transcending the trappings of class is about education, then it follows that something quite radical needs to happen, school dinners notwithstanding. Poor people don’t necessarily have the time, inclination or money to spend Saturday afternoons at the bohemian, ultra-expensive farmers’ market.

News came this week of a young man of 20 who died of malnutrition in Britain, having never eaten anything but chips, white toast and baked beans, a diet which caused fatal liver cirrhosis. The parents of children who only eat spaghetti hoops and chocolate spread please take note.

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