There are times when I cringe if a piece of science has been so over-simplified for public or children’s consumption that it’s simply wrong, or at best is an out-of-date picture.

The difficulty is deciding whether it’s better to have a poor picture than none at all. A good example would be the planetary model of the atom, where the electrons whiz around the outside in clean, well-defined orbits, just like planets around a star. This model was out of date 50 years ago, yet it’s what you will see time after time both in children’s science books and even in some adult-aimed science. Better than nothing? Perhaps, but misleading nonetheless.

Examples from physics are the ones that come most naturally to me, but the one that inspired this blog is ‘5 a day.’ This is a message being put across very strongly in the UK: you should eat five portions of fruit or vegetables a day. And certainly that’s a lot better than many people’s diets. But there does seem to be some evidence that it’s over simple as a useful message.

This is at two levels. One is that ‘five a day’ has been promoted very strongly as a catch phrase without always clearly explaining it. When talking to school children about it, some thought it meant five portions of fruit and five portions of veg per day. Others are confused about what a portion is. The website above has a section on ‘what counts as a portion’ but that doesn’t give very clear guidelines. I’ve heard it said that an (open?) fistful counts as portion, allowing for bigger portions as you get larger, but it’s not awfully straightforward.

The other problem is there is no distinction made between fruit and vegetables. Most of us could do to eat more fruit, but if you went for five portions of fruit a day, the chances are that you would be taking in an undesirably high hit of sugars – not as bad, certainly, as refined cane or beet sugar, but still not ideal.

The website above says ’What’s more there’s no limit to how much you can consume – so the more you eat, the better,’ and this just isn’t true. Anything can be taken to excess – it is possible for a vegan to overeat – and there certainly is a limit to the amount of fruit juice and fruit that it’s ideal to consume, thanks to those sugars.

Arguably that should be something like ‘at least 5 portions (portions are…) of fruit and veg, but preferably more than half vegetables, and make sure a couple are green leafy vegetables’… admittedly not so catchy, but arguably more informative.