Ultra-processed foods do NOT cause obesity, says US government's top diet advisors in bombshell review of current evidence: 'Studies have been biased'

Ultra-processed foods — demonized for years for their supposed effect on our waistlines — do not actually make people fat, according to a bombshell report.

The US government's top dietitians found 'limited' evidence these foods cause people to gain weight faster than any other food, after reviewing more than a dozen studies dating back to the 1990s.

The report has not been released in full and only segments have been uploaded online.

But the snippets suggest there is nothing intrinsic about processed food that causes obesity and that the amount of calories one eats is the most important factor for weight gain.

People have been hearing a lot about the health risks of ultra processed foods recently, which might make this report surprising, Carolyn Williams, a registered dietitian who was not involved in the review told DailyMail.com. 

Previous studies have linked ultra processed foods to cancer, diabetes, mental health conditions and obesity. According to the new report, the evidence that the foods cause obesity is not conclusive. 

The report comes from the US Dietary Guidelines Advisory Committee (DGAC), whose findings inform nutrition labels and public health recommendations for food.

'What they're saying is not that there is no relationship between ultra processed foods and larger body size or greater body fat,' Dr Williams told DailyMail.com. 

'They're saying, right now, we don't have enough conclusive research to come out and say, avoid all ultra processed foods.'

This report comes from a group of 20 nutrition experts from across the country that are elected by the Department of Health and Human Services and the US Department of Agriculture to draft new national nutrition recommendations. T

The current group has gathered to make recommendations about what Americans should eat from 2025 to 2030, this report will likely inform their new guidelines. 

They recommend that more research needs to be conducted before they are able to make rules about ultra processed foods. 

The report has yet to be made live online, but two slides were shared in a screenshot from Kevin D Hall, a nutrition scientist at the National Institutes of Health, in an X post. 

In their report, the DGCA said they had 'serious concerns' about bias in the studies that have linked ultra processed foods to weight gain. 

This is chiefly because the definition of ultra processed food isn't an exact science, which means that the studies may be subject to 'misclassification bias'. 

This means that studies that use variables that are hard to categorize may lead researchers to draw inaccurate conclusions. 

There is a system for classifying ultra processed foods, called NOVA, that was developed by Brazilian scientists who first started looking into the topic in the 1990's. But there's a lot of 'room for interpretation' in these guidelines, Dr Williams said. 

Generally if a food has ingredients you wouldn't use in home cooking - additives and stabilizers with long names, for example - then it's probably an ultra processed item. 

This system doesn't classify foods based on the nutritional content within them.

For example, mountain dew is ultra processed, which has next to zero nutritional benefit, but so are many brands of multigrain bread, which contain fiber, vitamins and even some protein.

This, nutritionists like Dr Williams said, brings the validity of ultra processed foods as a label into question. 

Dr Carolyn O'Connor, a Texas A&M epidemiologist who formerly worked at the Department of Agriculture and the National Institutes of Health, told The New York Times that certain kinds of UPF's are much more harmful than others, so grouping them all together makes it a lot less accurate of a measure. 

Ultra-processed foods are the sort of brightly packaged, aggressively marketed food and drinks that fill our supermarket shelves (stock photo)

'Sadly this is valid. Until we have one definition for ultra- processed, the body of evidence won’t provide a clear answer,' Connie Diekman, a registered dietitian who practices in Missouri, said in an X replying to the DGAC's findings. 

Another issue that the DGAC seems to have is that many of the studies they felt were robust enough to include in their review have taken place in other countries and only one study has been performed in a lab. 

Without laboratory studies of a topic, it's difficult for scientists to conclude that ultra processed foods are definitely causing health problems. 

Some commentators are striking back at the report, saying it doesn't address many of the other concerns people have about processed foods. 

Ultra processed foods have been linked to Type 2 diabetes, heart disease and mental health issues, a 2024 review from Australian researchers Deakin University found. 

The review looked at older studies - spanning roughly 10 million people in total - and found that ultra processed foods could be related to a number of bad health outcomes. 

This study was valuable, and increased Harvard T.H. Chan School of Public Health nutritionist Josiemer Mattei's belief that ultra processed foods could be a serious problem, told The NYT. 

The report also doesn't seem address the concern that these foods have been linked to cancer.  

A 2023 study from Imperial College London found the more ultra processed foods people reported eating, the more likely they were to develop all types of cancer. 

Eating highly sugary and fatty foods might dampen the affects of our genes that protect against cancer, a 2024 report from researchers in Singapore found.  

It's understandable that people would read this portion of the DGAC's report and react angrily, Dr Williams said. It doesn't seem in line with what most people have been hearing recently, but it represents how science works, she said. 

In her opinion, and many other dietitians, these foods likely have contributed to some of the public health problems we've been seeing in the US. But science is a slow process, and the body of research isn't 'definitively' there yet, she said. 

The report merely highlights that ultra processed foods need to be investigated further.

She added: 'This is really what you want. You don't want your federal committee jumping to conclusions.'