The definitive guide to cutting ultra-processed food from your diet

It is a scary thought that in 1980 when I went to medical school, only one in every 14 British adults was obese. Now it is close to one in four.

We didn’t see a lot of overweight patients when I was a medical student. These days, the NHS spends millions every year reinforcing beds, building bigger scanners and even designing larger mortuary fridges.

And this is only a fraction of the many billions spent treating and managing diseases caused by obesity, such as type 2 diabetes, arthritis and some types of cancer. So why, over the past 40 years, have we Brits become so fat?

I firmly believe the main culprit is our increasing reliance on unhealthy takeaways and ultra-processed junk food, which now makes up more than half of most people’s daily calories. Ultra-processed foods are the sort of brightly packaged, aggressively marketed food and drinks that fill our supermarket shelves.

If you look at the ingredients, they will typically be high in salt, fat and sugar, along with a list of mysterious ingredients you have almost certainly never heard of.

How bad is this food, really? Well, a few years ago I decided to put myself through an experiment for a TV documentary where I consumed an ultra-processed food diet for a couple of weeks.

I didn’t go crazy, I just switched to a diet where around half of my daily calories came from ultra-processed food. I went back to eating cereal for breakfast, sugary fruit yogurts, plenty of snacks – crisps, chocolate bars, biscuits and things like that – and some microwaveable frozen meals.

Several times a week I also went to a fast-food restaurant and had a burger and chips, with a Coke to wash it down, or fried chicken and chips, again with a sweet, fizzy drink. I had my weight, waist, blood sugars and blood pressure measured before starting on this diet, and then at the end of two weeks.

At the start I quite enjoyed it, eating the sort of food I hadn’t had for a long time. But I quickly noticed that within hours of eating, I would get hungry and crave more junk food.

I soon started sleeping badly, snoring loudly (according to my wife, Clare) and in a matter of days I felt far more lethargic than normal. I was tracking my blood sugar levels throughout the two weeks and, after only a couple of days in, they started to rise – alarmingly.

I was also feeling more anxious than normal, and that contributed to my need for more comfort food.

After two weeks, I did repeat tests. By now I had put on 6lb, my waist had expanded by around an inch and my blood sugar levels had soared into the diabetic range.

I had also developed high blood pressure, which alarmed my GP.

To counteract it all, I put myself on my own Fast 800 diet (a low-calorie diet based on eating plenty of healthy protein and fibre) and within ten days I had shed the weight.

And when I was retested, everything had returned to normal, which was a huge relief.

A friend of mine, Dr Chris van Tulleken, did something similar, but for four weeks. He put on more than a stone and the brain scans done before and after his experiment revealed that eating all that ultra-processed food had rewired his brain, encouraging him to seek out and eat even more of these unhealthy foods.

Chris managed to lose some of the weight he had put on, but who knows if his brain will ever fully recover.

He has since written a bestselling book, Ultra-Processed People, about the potential damage all of this is doing to our bodies and our mental health.

It is not just Chris and I banging this drum. Scientists across the world are beginning to link UPF foods to cancer, heart disease and other chronic diseases such as diabetes and high blood pressure.

One study published in The Lancet in November 2023 followed the diets of more than a quarter of a million people from seven countries across Europe for 11 years. It found that those who consumed the most processed foods had an increased risk of these problems compared with those who ate the least.

The top culprits were processed meat and fizzy drinks – which may not come as a surprise to most people.

But what about the rest of the foods we put in our shopping baskets without thinking?

How can the average shopper work out whether something is ultra-processed or not – and does it really matter?

It’s worth saying at this point that most experts don’t all agree on a definition.

Some claim that if a food product contains at least one ingredient you don’t usually find in a kitchen, it’s UPF.

Others claim anything wrapped in plastic and made at an industrial scale counts because the processes they go through strip the food of its nutrients and fibre – leaving behind lots of calories and little else.

At the moment, the most scientific approach uses what is known as the NOVA classification system, developed by the Brazilian professor of nutrition and public health Carlos Monteiro. This splits all food into four distinct categories.

Monteiro noticed that people in his native country’s rural communities had begun to pile on the pounds after being given access to packaged and processed food for the first time.

The NOVA principles are simple. The first category, Group 1, is for food that is ‘unprocessed or minimally processed’ – mainly, food found in nature.

This might include fruit and vegetables, meat and fish, but also other things that have undergone a degree of processing – pasteurisation, freezing, grinding or milling – foods such as milk, flour and pasta.

Group 2 is for the kinds of ingredients you might use to cook in your kitchen – which includes oils, butter, sugar, salt, honey and vinegar – but we don’t tend to eat these by themselves.

Food that combines Group 1 and Group 2 appears in Group 3 – in other words, food that has been processed, but not necessarily to a point that it becomes unhealthy or unrecognisable. Most cheese is in this category, along with tinned or frozen vegetables, fruit and beans.

The final category, Group 4, is what most people think of as ultra-processed foods.

These contain very little, if any, intact whole foods from Group 1, and will likely have a long list of unfamiliar ingredients and additives that you wouldn’t recognise from your kitchen.

These might include preservatives, emulsifiers and flavour enhancers; substances to thicken, sweeten and colour, or soften.

There’s a theory that food that is created to be soft and easy to chew and is dense in calories, makes you want to eat more of it. It stops your stomach signalling that you’re full, so you keep going. It could even be addictive.

You can also spot a UPF because it will be conveniently ready-to-eat or heat, and is often packaged attractively.

So should we all be cutting UPFs from our diet completely?

Purists would say so, and that we should cook only from scratch or eat minimally processed ready-made foods.

But given that many are staples – such as sliced bread, breakfast cereals, yogurts, sauces, and even cheeses – that might not always be easy or realistic.

Unless you are savvy it can be more expensive, as research shows that going UPF-free can often increase the price of a weekly shop.

And who doesn’t simply run out of time and resort to an emergency frozen pizza or microwave meal every now and then?

Is there a way to avoid UPFs, or simply cut down and not complicate life unnecessarily? The answer is yes.

I gather, for example, that some supermarkets now stock sliced bread that they claim is totally UPF-free, or at least lower in UPF-type ingredients than others.

And though our most popular breakfast cereal, Weetabix, contains malted barley extract, a flavour enhancer that makes it a UPF, Shredded Wheat is just wheat, so it is UPF-free (of course, adding a huge amount of sugar before eating it would negate the benefits).

And what about things such as soft cheese?

Philadelphia, the UK’s favourite cream cheese, according to supermarket analysts The Grocer, is most certainly a UPF, containing a thickener called guar gum, also known as E412 (food additives used to be given ‘E-numbers’, which made them easier to spot – more on this over the following pages) along with the preservative citric acid.

But Sainsbury’s own brand White Soft Cheese spread is made with just a single ingredient: milk. Processed, yes, but not UPF.

To cut through the confusion on this subject, and to help you make the most well-informed choices next time you go to the supermarket, read on.

We’ve spoken to experts in food science to produce a definitive guide to the main items in your weekly shop.

And not only will it help you work out what counts as UPF and why, but it will also reveal which of them you might not need to worry so much about after all.