"We only really recently have evidence for sugar, on its own, causing diabetes."

OK. But first let me say most of what follows about health I learned in the 1960s, back then it was common knowledge and discussed in schools, newspaper reports and on radio talk shows, etc. As I was reasonably healthy I wasn't given any special advice or instructions so the info I received was essentially the same as everybody else.

The big questions are how strong or irrefutable does evidence have to be before we act on it or take it seriously, and what disruptive factors interfere with our considerarion of said evidence. It's probably best to illustrate this with a couple of examples from when I was at school. Around that time carbon tetrachloride/CCl4 was commonly used in dry cleaning shops and one could wiff it as one passed by. It was also the time when health worries about using CCl4 for cleaning became a prominent issue and phasing it out for safer alternatives started.

In highschool chemistry we were instructed that CCl4 was toxic and to avoid getting it on one's skin and not to breathe its fumes. This led some kids including myself to ask why is it toxic when it's so inert (with four Cl atoms and no hydrogen versus say DCM/CH2Cl2—with its two hydrogens DCM would be more reactive, thus it would seem to be more harmful but whilst still harmful it's less so). The teacher said he wasn't sure why CCl4 was so harmful but went on to say it affects the liver and probably has something to do with upsetting fats as they are very soluble in it, he did not mention it was a likely carcinogen. We accepted that answer.

Then there was the matter of benzene/C6H6, he said it was very toxic and a known carcinogen, and it could be absorbed through the skin and its vapors breathed in. To make matters worse it is often a constituent of other solvents and fuels, gasoline for instance. He stressed repeatedly that we must handle it carefully and take precautions especially so if we were to become chemists as we'd likely have access to it more frequently and in higher concentration than most others. I still recall him holding up a small sealed bottle of it while he spoke about it.

This raised similar questions as to why C6H6 was dangerous whilst many compounds containing benzene rings are either not poisonous or are much less so than benzene (and of course some are even more so).

This is where the teacher was out of is depth and said we're not toxicology experts so we just have to accept the evidence that many of these chemicals are dangerous and especially so benzene. He then went on to state a general safety rule that we should always apply which is to treat all aromatics, petroleum-like chemicals (which back then also contained Pb/TEL) and chlorinated hydrocarbon compounds as toxic, dangerous and flammable. This applies to everyone, not just chemists—painters and industrial workers are also at risk of exposure to many different types of volatile solvents. That and related safety mantra was drummed into us often.

That general rule I've applied ever since and I'm still a living member of this planet despite the fact that I've used many different toxic solvents over the years.

The point of all that is we are often not fully aware of the dangers of these chemicals but there is a 'smoking gun' that manifests out of observation and statistics, that is the harm they've caused to others. Even back in the '60s when the biochemistry of chemicals such as CCl4 and C6H6 was much less well understood than today toxicologists and biochemists considered the causal link between past exposure to them and illness strong enough to warn and where necessary act to minimize harm. Definitive proof wasn't need to act.

Similar but less forceful instructions were applied to smoking. Back then cancer was hardly mentioned (despite evidence from the early '50s of the link) but we were told at school not to smoke because we would likely get lung disease which would shorten our lives. (BTW, I don't smoke.)

And there was a similar message with NaCl. 'Do not use or put too much salt on your food' was a common lecture of the time from both parents and teachers—'you'll get hardened arteries and high blood pressure if you do.' Moreover, this understanding was around long before I was born yet in the 1980s some authorities modified this to say it only applied to a percentage of the population who were susceptible and that most of us didn't have to worry about our salt intake levels. This dangerous message was reversed in the '90s. One wonders how much damage it caused. A question remains about how this wrong and corrupt message took hold in the first instance when the 'facts' as stated were so evidently wrong (so contrary to longstanding evidence).

I'd note it seems not much has changed since the reversal as so much commercially prepared food still contains hugh amounts of salt. Forget health effects for a moment, I find much of this food too salty for my liking and in some instances it's just too salty for me to eat.

On the matter of fat, you're right. By the 1960s fat was a hot ropic mainly because it was linked to heart disease. I recall in our household my father switching to margarine which later turned out to be questionable but the rest of us continued to use butter, albeit sparingly. My mother always discouraged heavy butter usage and spread it thinly. With meat-based soups etc. she'd always let them settle and skim off the fat. Same with fried foods, they'd be patted with paper towels to remove any excess fat (note she was not faddish about the practice because she was concerned about getting fat—she was naturally skinny—but rather because she was following long-held advice). I say that because my mother's concern with fat long predated the 1960s fat scare as my grandmother did exactly the same. Clearly my mother had learned the 'dangers' of fat from her mother so that meme goes back at least a century I'd reckon.

No doubt misleading information from vested commercial interests pressured much of society to act not in its best interests but two things stand out in these debates. The first is why the medical profession, health departments, statisticians, etc. didn't speak out in unison and with more force as it would have saved many lives (and on evidence they still don't do so). Medical statistics alone ought to have been a sufficient smoking gun for governments to act, but they didn't.

Second, education in these matters from a young age by both parents and schools is essential. In my case, one thing stands out which is that we kids were not only told what was bad for us but also we were given clear reasons for why they were so. Logical reasons for why we should act in our best interests are much more effective than some nebulous edict without explanation saying 'don't do it'.

I am still unclear as to exactly why these health messages became so derailed from around the 1970s onwards. It's always been clear to me that health issues surrounding fats and sugar were always separate despite them having many common factors and interactions. So why was such a simple notion so hard to explain to a lay public? (I have my theories but I'll leave them for now.)

With sugar we kids were taught all the usual facts at school: rotting teeth, getting fat and the risk of diabetes, but perhaps what made those facts sink in and last a lifetime was that as the same time we were taught the heroic story of how Charles Best and Frederick Banting separated insulin in 1922 and immediately saved lives. This history was even more poignant to us as one our classmates had type-1 diabetes and it was obvious to all that he wouldn't be alive but for them. Both facts sharpened our minds about the dangers of high sugar intake.

Again, for me it seems something went wrong with the education system, and it was made worse when professionals went off course and changed health messages midstream, they made the disaster worse.