What happened when I ate ultra-processed food for a month
Over half the energy from food eaten in the UK is believed to come from ultra-processed products. There are concerns these foods lead people to eat more and put on weight. One in four adults in the UK is estimated to be obese, as well as one in five children aged ten to eleven.
“I wanted to find out what effect a diet high in ultra-processed food had on me”, says Dr Chris Van Tulleken, presenter of What are we Feeding our Kids? (BBC One Thursday 27 May 9pm). There is little research on how ultra-processed foods interact with our bodies, especially among children and teenagers, who eat more than the average adult.
For the experiment, which is shown on the documentary, Chris increased his usual intake of 30 percent ultra-processed foods to 80 percent for four weeks. “It sounds extreme, but it’s the diet one in five people in the UK eats”, he says.
After the month was over, Chris reported poor sleep, heart burn, unhappy feelings, anxiety, sluggishness, and a low libido. He also had piles from constipation. “I felt ten years older”, he says, but “didn’t realise it was all [because of] the food until I stopped eating the diet”.
Chris gained almost 7kg in the four weeks and moved from a healthy weight to overweight. “If the weight gain continued at that rate for six months, I would have gained six stone”, he says. It didn’t stop there.
Brain activity scans showed the areas of Chris’ brain responsible for reward had linked up with the areas that drive repetitive, automatic behaviour. “Eating ultra-processed food became something my brain simply tells me to do, without me even wanting it”, he says, adding this is a similar brain response to taking substances we consider classically addictive such as cigarettes, alcohol and drugs. The changes in brain activity weren’t permanent, but “if it can do that in four weeks to my 42-year-old brain, what is it doing to the fragile developing brains of our children”, he says.
We don’t know exactly why ultra-processed foods have these effects, but Chris says most hypotheses come down to a combination of the physical act of processing and their nutrient make-up.
Impact on how much we eat
Chris talks to Dr Kevin Hall, a senior investigator for the National Institute of Health, on the documentary. For research, Dr Hall tested two diets that were matched in terms of fat, sugar, salt and fibre content, but one was made up of unprocessed foods and the other of around 80 percent ultra-processed foods. The participants were able to eat the foods on offer until they wanted to stop.
His study found “folks eating the ultra-processed diet ended up eating more than 500 calories per day more [and] gained almost a kilo of body weight over two weeks”, says Hall. Blood tests showed an increase in the hormone responsible for hunger and a decrease in the hormone that makes us feel full among the participants eating the diet high in ultra-processed foods. These results were consistent with Chris’ experience – his hunger hormone increased by 30 percent during his experiment, which may have encouraged over consumption.
Hall also found participants on the ultra-processed diet ate much more quickly than those on the minimally processed diet, which may have contributed to the consumption of more calories. Chris experienced this too, as many of the “foods are so easy to chew and swallow”. Previous studies have suggested eating slowly decreases hunger.
‘It’s really hard to stop eating’
“I found myself craving food much more often”, says Chris. Research has previously found some foods, including ultra-processed pizzas, chocolate, crisps and cakes, can elicit cravings, loss of control, and inability to cut back.
There is evidence foods high in carbohydrates and fat (as many ultra-processed foods are) can trigger the centres of the brain responsible for reward, emotion and motivation. A brain imaging study suggests the more often you experience reward from foods, the more you have to consume to sustain the same enjoyment.
Many ultra-processed foods have also gone through focus groups to make them ‘perfect’. The taste, level of saltiness, mouthfeel, chew, and even the sound it makes when eaten, may have been fine-tuned. “I don’t think anyone at any food company set out with the intention of making people gain weight”, says Chris, adding a “side-effect of really delicious food is that it’s really hard to stop eating it”.
Should we avoid all ultra-processed foods?
Foods can be categorised as minimally or unprocessed (for example, tomatoes), processed (tinned tomatoes) and ultra-processed (store-bought tomato pasta sauce). Some ultra-processed foods are healthier than others – wholegrain breakfast cereals, wholemeal sliced bread, tinned baked beans, and unsweetened soy or plant-based drinks, are all ultra-processed but have nutritional benefits. Similarly, ready-made pasta sauces, ready meals, spreads and sliced meats can be healthy.
Some pre-prepared foods are not ultra-processed, but any that include additives and chemicals not used in home cooking probably are. The availability, convenience and marketing of ultra-processed food makes it “almost impossible” to eliminate, says Chris.
Although a diet high in ultra-processed foods is not recommended, eating them on occasion is unlikely to cause a risk to health, according to dietitian Ro Huntriss. “Having a healthy diet is all about balance”, she says.