A new paper has statistically linked inflammatory bowel disease, an umbrella term for chronic inflammation of the digestive tract, to processed foods. But because every food is processed - no one eats wheat that hasn't been milled - the term has now become "ultra-processed."

They do so by noting that IBD is more common in industrialized countries. While this is true, so is medical care of all kinds. Every condition is more diagnosed in industrial countries and the richest of them all, the US, has more diagnoses than anyone else. To try and create a link between foods with higher levels of added sugar, fat and salt and inflammation, they went to the Prospective Urban Rural Epidemiology (PURE) study, a diary kept by people who self-report their food intake, and looked at answers from 116,087 adults aged 35-70 years. Between 2003 and 2016, 467 participants developed IBD (90 with Crohn's disease and 377 with ulcerative colitis.) 

Enough  reported eating ultra-processed foods that the authors could create statistical significance. 

There are a number of confounders. Since these are surveys, they can only be considered observational. Science has not shown that packaged baked goods will cause IBD but the same food you make at home won't. While some people report that fizzy drinks, sugary cereals, or hot dogs can aggravate IBD, no studies have found it to be causal. Many people also get flare-ups eating beans and fruit. Every IBD sufferer has learned to create their own diet.

The number of people diagnosed with it over the survey period is so small (500 out of nearly 120,000), any changes can look spectacular. For example,  those who said on the survey they ate 5 or more servings of processed food had 82% increased risk of being diagnosed with IBD during the period but even only one serving meant a 67% increased risk - that means they were likely going to get a diagnosis no matter what. Yet people who ate red meat, white meat, and starches did not show an increased link to a diagnosis, which many who suffer chronic inflammation of their digestive tract will say is not valid.

That leaves the epidemiologists with speculation that the ill-defined "ultra-processed" category might be the culprit, but without much evidence for it.