Ultra-processed foods make it harder to lose weight

Obesity researchers in London have found that eating ultra processed foods makes it harder to lose weight. These foods are manufactured for convenience, and often contain high levels of sugar and unsaturated fats. But a new study - which has been published in Nature Medicine -  found that a diet of less processed food may be more beneficial for weight loss. Here’s Sam Dicken at University College London…

Sam - So we've seen growing evidence around higher intakes of ultra-processed foods. So these are foods that are made with the purpose of being highly profitable, so they're very cheap, accessible and tasty and want you coming back for more. Typically, these foods are very nutritionally poor, but actually some of these ultra-processed foods are nutritionally better. And no one's actually looked yet at whether ultra-processed foods that meet our current dietary guidance can be healthy. So we put that to the test.

Chris - How did you test it?

Sam - The best way to test diets and interventions is to do a clinical trial. So we gave participants a healthy balanced diet based on the current NHS guidance, that's having your five portions of fruit and veg a day, not eating too many foods high in saturated fat, sugar and salt, and having the recommended fibre intakes. We provided these diets, one ultra-processed one minimally processed. These are the kinds of meals that you make from scratch at home with raw ingredients. And they were provided for free, delivered twice a week to participants' homes. We removed all these barriers that people face when accessing a healthy diet. So we provide it for free, ready prepared and with a menu guide. And what we wanted participants to do was to have as much or as little as they wanted of these diets. Because we think ultra-processed foods get people to eat more than they need. So we're going to test that in the context of the current dietary guidance.

Chris - Were the people trying to lose weight or gain weight? What was their health status before you started on this trial?

Sam - So our participants were living with being overweight or obese. So that's the body mass index between 25 and 40 kilograms per metre squared. So it's your weight divided by your height squared. And the average person in the UK has a BMI of around 26 to 27. And participants were not told that the trial we're looking at weight as the primary outcome, our main outcome of interest. And participants were not told to restrict their intake. We provided more energy than they needed in abundance of these two healthy balanced diets. And they were just told to eat as much or as little as they wanted until they felt satisfied and full.

Chris - So basically, you're presenting these people for one period of time with a really wholesome, healthy diet made from minimally processed foods that they would want to eat. And then the rest of the trial, you're doing the same thing, but with ultra-processed ingredients. And the outcome measure is does their weight change?

Sam - Exactly that. So the one diet minimally processed, the kind of food you think of is to be healthy. And the ultra-processed diet might be high fibre breakfast cereals, nutritionally improved sandwiches and meal deals, ready meals and snack bars, but all meeting our current guidance.

Chris - So what happened then? Did you see a difference?

Sam - Really interestingly, we saw that on both diets, people ate less than they were before they started the trial. Most probably because the diets they were eating before weren't aligned with our current dietary guidance. They were eating too much saturated fat, sugar and salt, and not enough fruit and veg. These nutritionally improved diets, whether ultra-processed or minimally processed, resulted in significant weight loss. What's really interesting is when participants had the minimally processed diet, they lost twice as much weight, significantly more weight loss than the ultra-processed diet.

Chris - This is really interesting. So ultra-processed foods are not necessarily awful then, they can, in the right hands and mouths, translate into a loss of weight, but they're still not as good as if you make food from scratch. I mean, that's the take-home from this then.

Sam - It is indeed. And a good way to think about this is, not all ultra-processed foods are intrinsically unhealthy, but there's an effect. When that food has had the purpose of being made to be highly profitable, tasty, cheap and accessible, we tend to see that there's an effect on how much we eat and weight change compared to the same food if it wasn't going through this same process.

Chris - Did the participants eat roughly the same amounts on both diets or did they lose more weight on the minimally processed foods because they ate less of it, because actually they enjoyed it less?

Sam - There were two ways we estimated their energy intakes on the trial. We asked them through dietary reports, which can sometimes be a bit inaccurate because people tend to under-report. The other way is that we based it on the amount of change in their muscle mass and fat mass that changed across the diets. And we saw that there was a significant reduction in their energy intake on the ultra-processed diet from baseline, but a significantly greater reduction in their energy intake on the minimally processed diet compared to baseline and the ultra-processed diet.

Chris - What's the take home from this then, as opposed to take away? I suppose you could say, we've got a population of the world actually that are overweight and obese at extreme levels now, and we're trying to combat this. What does this study add? What should people do differently?

Sam - We know that the biggest barriers to accessing healthy food is cost. In the UK, the lowest 20% of people in terms of income have to spend 70% of their disposable income to meet our current dietary guidance, compared to 10% of the highest 20% of income. And that was reported in the Food Foundation Broken Plate Report earlier this year. So what we need to do is clearly our current dietary guidance works, but it seems to be more favorable. We get greater weight loss and other aspects when it's a minimally processed diet. So we need high level action from governments to change the financial drivers that dominate our food supply. And rather than just being purely driven by profit, also have health and the environment as stakeholders. So we're developing foods that are incentivized to improve our health and not just our back pockets.

Chris - So at the moment, someone who goes into a convenience store and they're hungry because it's the end of the day, they've got a family to feed, they're in a hurry, they're going to reach for the ultra-processed ready meals and so on, because that's the easy option. It's also often the cheaper option. If we can flip that round, you're saying, and this study kind of suggests that we're eating more minimally processed ingredients and making more meals from scratch, which are at the moment more expensive. So if we could make them cheaper, and therefore there would be a price incentive to consume them more, you're arguing that would be a double win, because we would be healthier, and the weight loss that people would achieve, or at least not gaining as much weight would be greater.

Sam - Indeed, it seems to be a more cost effective approach to improving diets. And globally, we see that it's a lack of healthy food. So fruits, vegetables, whole grains, fibre, that's linked with early mortality and greater disease, and the more so than unhealthy components, we really need to think about how we're improving access to healthy foods, but not by individuals, by systems and governments and communities.