Sometimes things get repeated so often they become accepted as truth.
Clearly this has become a legitimate strategy for more than one Government around the world.
On a more day-to-day level, there are lots of food stories we tell each other and ourselves that we simply accept.
One of these is the idea we need eight glasses of water a day.
How many hundreds of times have you heard this?
Two litres a day, they say, or we will not function properly. We'll get dehydrated, we'll get the dreaded "brain fog" and we'll appear wrinkly and tired.
We're all so scared of not drinking enough water that we carry around supplies to suck down all day long.
It's hard to believe this hasn't always been the case.
But I can remember living in the US in the mid-90s and being amazed at the aisle of water in the supermarket.
All those cute little individual bottles. I'd never seen anything like it. I even brought a bottle back home with me.
Shortly thereafter, the bottled water industry in New Zealand took off (nothing to do with me).
In fact, there is no scientific basis for the eight glasses a day maxim.
There have even been papers published showing this to be a myth. A 2007 paper covered other medical myths as well, like the one that we only use 10 per cent of our brains.
It's thought the eight glasses myth started in 1945, when people wrongly interpreted advice about how much fluid we need.
One of the authors of the 2007 paper, Aaron E Carroll, has written further about this.
"Contrary to many stories you may hear," he wrote in the New York Times, "there's no real scientific proof that, for otherwise healthy people, drinking extra water has any health benefits."
He cited reviews finding no benefit from drinking water to skin hydration or the appearance of wrinkles, or to kidney function.
He also advised we don't need to worry about walking around in a dehydrated state.
"The human body is finely tuned to signal you to drink long before you are actually dehydrated."
So should we just throw away our water bottles? It probably wouldn't hurt.
There's no official recommendation about how much water we should drink - it varies depending on how big we are, what we're doing and where.
We can get fluid from other sources. It's in the foods we eat - carrots and courgettes, for example, are over 90 per cent water - and in non-water drinks, too.
I get most of my daily fluid from green and black tea (which, no, isn't dehydrating, as another myth goes).
This is not to be anti-water.
Every expert would agree water should be our first choice of beverage, and certainly our kids' first choice. Water is a hands-down better choice than any sugar-sweetened beverage.
But we don't need to get stressed if we're not glugging two litres a day.