Sanjay buys a packet of crisps. He tells himself he will save them for later - but then decides to eat just one or two. Then he has a third, and a fourth... before he knows it, the whole packet is gone.

In his book Ultra-Processed People, Chris van Tulleken explains why Sanjay is unable to stop himself. The food industry has spent years making sure he cannot.

The book is about ultra-processed foods - UPFs for short. These include chemicals which are designed to trick the body. As a result we long for more of the food and do not recognise when we are full.

Take Pringles, which have 22 ingredients. They include acids which, in natural food, tell the body that some good proteinLarge biomolecules made of up amino acids, which in turn are made up of DNA. is coming its way: the kind you might get from fish or a meaty soup.

People in Britain get around 60% of their caloriesThe amount of energy released when your body digests and absorbs food. The more calories a food has, the more energy it gives your body. from UPFs. Some of these come in takeaways and ready meals. But they are also in things we eat every day like  cereal, ice-cream or cheap supermarket bread.

Chris van Tulleken has a personal interest in this. He has a twin brother, Xand, who until last year was addicted to UPFs. As a result, he was was 30lbs heavier than Chris.

As part of his research, Chris van Tulleken spent a month eating UPFs. By the end of it, he writes: "I felt like I'd aged ten years. I was aching, exhausted, miserable and angry."

Defenders of UPFs deny that they are addictiveSo enjoyable that you do not want to stop.. They say that the extra ingredients make food cheaper to produce and keep it fresh longer.

They also say that rich people like van Tulleken do not understand how vital this is to families who struggle to make ends meet.

In the 1960s, families in the US spent 16% of the money they had to spare on buying food. By 2021 it was down to 10.3%.

Henry Dimbleby, a food adviser to the UK government, says that 60% of British people are overweight.

Yes: It is all very well telling people not to eat cheap ultra-processed food - many families cannot afford anything else. That is why British politician Keir Starmer has ruled out a sugar tax if Labour wins power.

No: Eating well is essential. Buying cheap UPFs is a false economy - it is more than likely to lead to health problems such as diabetesA medical condition causing there to be too much sugar in the blood. and obesityThe medical condition of being very overweight. There are many ways of measuring this, including a BMI of 30 or more. (You can work out your BMI by dividing your weight in kilograms by your height in metres squared.) which will make it hard to earn a living.

Or... It depends how you define "well". You can eat healthily for very little money if you cook your own food and stick to simple dishes. A good cook can make delicious food from inexpensive ingredients.