In healthcare we are much concerned about privacy, but Sainsbury’s, the supermarket chain, knows how much toilet paper I’ve bought in the past 20 years, how many chocolate éclairs I eat a month, that I love smoked fish, whether I eat white or brown bread, and much more. It could probably do a better job of predicting my life expectancy than my GP. So why don’t they and other supermarkets make a bigger contribution to health? I propose that they do. (I wrote this on New Year’s Eve and was more shocked than pleased to discover on 2 January that I’d been thinking in the same way as the government.)
I was thinking this as I was checking out this afternoon. I’m given a receipt that details everything that I’ve bought with the cost, the amount of money I’ve “saved” by buying discounted products, and the number of loyalty points I’ve accrued. And now, an innovation, I’m told how much money I have saved by shopping in Sainsbury’s rather than other supermarket chains—or if I’ve paid more I’m given a voucher to that amount to use on my next purchases.

Sainsbury’s own products do have the traffic light system, telling me how many calories and how much fat, saturated fat, salt, and sugar is in a portion, and whether this is healthy (green), unhealthy (red), or in the middle (orange). (The peanut butter I have for breakfast every morning looks lethal.) The supermarket could easily include this information against every product on my receipt, but that would surely be too much information to be useful.

A better nudge might be to add it all up and give me a green, orange, or red receipt. I often make my own calculation as I look at people’s baskets. The one with three bottles of vodka, a loaf of white bread, a tin of corned meat, and four packets of cigarettes screams red. Two grapefruit and a cucumber would be smugly green, but  many baskets, particularly the big ones that are a weekly shop, are harder to calculate. A coloured receipt would, of course, be visible to all, making it perhaps an effective “nudge.”

But the supermarket might be wary of “shaming” its customers with red receipts, so perhaps an overall score would be better—perhaps out of 100. Such a score would also give you much more information than the traffic light system, and you might take pleasure in edging your score ever higher. The receipt might even make suggestions on how you could raise your score—perhaps based on the supermarket’s knowledge of healthy foods that you have bought before.

The supermarket knows all your previous purchases, so it could give you information on the present purchase in relation to previous scores, perhaps as a graph, or an overall score on all your purchases for the past year. You could also be given information that relates your purchases to those bought by everybody else using that supermarket or in your postcode or to the healthiest people in Britain. Your whole supermarket might be given a score, opening up the possibility of competition among communities as well as among individuals and of each individual against him or herself.

If they wanted to, supermarkets could go even further, giving people more loyalty points for buying healthy products. No doubt if supermarkets wanted to be “in the health business” they would come up with a hundred clever schemes to promote healthy purchasing. The extraordinary data they have would allow them very quickly to see which were the most effective, and competition among supermarkets would further drive healthy purchasing.

But do they want to be in the health business? They certainly don’t want to be in the disease business, although they are, but they are likely to be fearful of being accused of “nannying” and they won’t want to discourage those who purchase mainly unhealthy products. And there may be many false signals—for example, to those who buy all their fruit and vegetables at farmers’ markets and only cat food at the supermarket.

There is, however, growing interest in diet as a major driver of health, and supermarkets can surely make money from being in the health business. The trick may be to concentrate on the positive in the way that condoms are marketed as jumbo, colossal, and supercolossal. There are no small penises.

RS was the editor of the BMJ until 2004 and is director of the United Health Group’s chronic disease initiative.