Ultra-processed foods lead people to eat more and put on weight, the first trial to assess their impact suggests. Volunteers had every morsel of food they ate monitored for a month. And when given ultra-processed food, they ate 500 calories a day more than when they were given unprocessed meals.
The US National Institutes of Health said ultra-processed foods may be affecting hunger hormones in the body, leading people to keep eating.
There are scientific arguments about the definition of ultra-processed food but lead researcher Dr Kevin Hall said it was like “pornography – it’s hard to define but you know it when you see it”.
Warning signs include:
- ingredients you cannot pronounce
- more than five ingredients listed on the packet
- anything your grandmother would not recognise as food
Twenty people gave up a month of their time to live in a laboratory.
For a fortnight they were given either ultra-processed meals or unprocessed ones and then the diets were switched for the second half of the study.
The participants were allowed to eat as much as they wanted and researchers closely monitored what passed their lips.
During their ultra-processed foods fortnight, the volunteers, on average, ate an extra 508 calories a day and put on 2lb (1kg).
Dr Hall, from the National Institute of Diabetes and Digestive and Kidney Diseases, told reporters: “This is the first study to demonstrate that there there is a causal relationship.
“Ultra-processed foods led to increases in calorie intake and in body weight and in fat.
“It’s suggestive that this may be playing a role in the larger population.”
Dr Hall said previous studies had estimated the “obesity epidemic” in the US was caused by people eating an extra 250-300 calories a day.
The explanation is, for now, elusive.
The human guinea pigs reported both meals were equally tasty, so a preference for ultra-processed was not to blame.
The nutritional content of the two diets was also carefully matched to ensure they had equal amounts of sugars, other carbohydrates, fats and fibre.
One potential explanation is the impact of industrially processed foods on the hormones that alter the desire to eat.
Dr Hall said: “When people were consuming the unprocessed diet, one of the appetite-suppression hormones (called PYY) that has been shown in other studies to be related to restraining people’s appetite actually went up despite the fact that they’re now eating less calories.”
The study also showed the levels of the hunger hormone ghrelin went down on the unprocessed diet..
Does this explain the obesity crisis?
The study is on a limited number of people only and for a short period of time, so it is unclear if the findings apply more broadly.
Some people on the diet ate an extra 1,500 calories on the ultra-processed diet, while others ate roughly the same.
Dr Gunter Kuhnle, from the University of Reading, said processing food was often important “for palatability, safety and preservation”.
He said: “This is a well designed and well conducted study with interesting, although perhaps not surprising, outcomes.
“It seems that participants found ultra-processed food more palatable, ate more quickly and consequently more – possibly because it took longer for them to feel full.
“A very interesting outcome of the study is the cost-per-energy: the ultra-processed diet was considerably cheaper than the unprocessed control diet, and this is likely to have implications from a public health point of view.”
What we eat has a big impact on our health, and ultra-processed foods like candy, soft drinks, pizza and chips do not contain enough of the beneficial nutrients that the body requires. The more ultra-processed foods we eat, the poorer the overall nutritional quality of our diet.
But here’s the good news. Not every food that comes in a box is ultra-processed. Confused?. But this list is a classification system called NOVA that was developed by an international panel of food scientists and researchers. It splits foods into four categories:
Unprocessed or minimally processed foods: Think vegetables, grains, legumes, fruits, nuts, meats, seafood, eggs and milk. Make these real, whole foods the basis of your diet.
Processed culinary ingredients: These items make plain vegetables and a grilled chicken breast taste a whole lot better. Examples are herbs, spices, balsamic vinegar, garlic and oil. Use these ingredients in small amounts to create fresh, home-cooked meals.
Processed foods: When ingredients such as oil, sugar or herbs are added to foods and they are packaged, the result is processed foods. Examples are simple bread, cheese, tofu, and canned tuna or beans. These foods have been altered, but not in a way that’s detrimental to health. They are convenient and help you build nutritious meals. See? Not everything in a package is bad for you!
Ultra-processed foods: Here’s the category where almost 50% of our calories come from – and where we should cut back. These foods go through multiple processes (extrusion, molding, milling, etc.), contain many added ingredients and are highly manipulated. Examples are soft drinks, chips, chocolate, candy, ice-cream, sweetened breakfast cereals, packaged soups, chicken nuggets, hotdogs, fries and more.
How can I cut back on ultra-processed foods?
Cook more often: One major change in dietary patterns in the last 70 years has been the decline of home cooked meals, and the increase in ultra-processed foods. Tip the balance! Cook at home more often, without using ultra-processed ingredients (heating up frozen fried chicken doesn’t count).
Dine with friends and family: Real food, real talk, good company. That’s a winning combination for dinner – and studies show that people who dine together have better eating habits, such as enjoying more vegetables, fewer soft drinks, and less deep-fried food.