It's so easy to be sucked in by a bargain such as 'buy one get one free', or even one that's less of a good deal such as 'supersize your order for only 30p'. At the time of purchase, our brains switch off (at least the part that can see reason) and since we were going to buy the product anyway, getting more of it seems like a good idea. But campaigners claim that this kind of marketing ploy is as damaging to our health as happy hours in pubs.

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Supermarkets have long been trying to flog us discounted junk foods and rarely do we see two-for-ones on healthy foods. And now even when making non-food purchases, retailers try to throw in a half-price supersized chocolate bar.

Recent research showed that supermarkets offer three times as many unhealthy food discounts than healthy foods.

Nutritionist and obesity campaigner Zoe Harcombe said: "The supermarkets pounce on us at every opportunity and feed the obesity epidemic on their way to profits. Pushing this sort of processed food is as bad for health as selling drinks cheap or offering double measures. There was rightly an outcry about that, there should be similar concern about this."

She added: "You don't see 'Buy an apple, get one free'. But we are absolutely deluged with bars of chocolate, bags of crisps, bigger drinks and muffins.

"It is difficult to understand how we can be quite so evil to our fellow human beings. It should be outlawed. If someone said 'Have free cigarettes with your purchase' everyone would be outraged.

"There are no free or cheap offers on natural food because there is no margin in it.

"There is a margin in junk food so they discount to shift more of it. This is bad for the nation's wellbeing, fuels obesity and ends up costing the health service a fortune."

So while retailers get fat off their profits, we just get fat.

And it's so easy for them to sell to us, according to psychologist Dr David Lewis-Hodgson of consumer research consultancy MindLab International.

He said: "The easiest person to sell to is someone who has already said yes.

"So we are at our weakest when we have ordered a cappuccino and are being offered a muffin, cake or bagel. The appetite centre of our brain has been activated and we don't tend to think about the 700 calories that come with the full-cream doughnut we are being offered.

"They are in it to make money. Retailers are falling over themselves to make us feel good about being in their shops so they can shift products off the shelves."

The nation's current state of health is not looking good. All those extra cakes and chocolates have increased our obesity rate to 24 per cent of the population and the estimated cost to the NHS for treating obesity-related illnesses is over £4 billion a year.

Perhaps that buy one get one free is looking like less of a bargain now.

Do you think retailers have a responsibility to think about their customers' health or are they within their rights to try to make profits? Leave a comment and share your thoughts.