The processed food "craze" (if we can call it that) was already well into the full swing by before 1990.
From 1970's and beyond, that's when the obesity rate started noticeably jumping up.
The article I linked before mentioned that perhaps the increase in microplastics could be a factor. However, I'm thinking that's just an preliminary inquiry on their part since it's just now gaining more attention.
I've personally wondered if perhaps overuse of antibiotics has had something to do it. Since there does appear to be at least something of an association between these cancers and disruption to the gut bacteria... Broad-spectrum antibiotics like the ones that are commonly used (and often overused) are certainly gut bacteria killers, as they go "scorched earth" on all bacteria (good or bad).
The 90's was the era where the term "antibiotic resistance" started making it into the mainstream, with the CDC having to issue warning and increased guidance. For those who remember the mid-90's awareness campaign by the CDC "Get Smart: Know When Antibiotics Work".
They did that because there were tons of people getting them prescribed when they weren't necessary.
In an NIH study reviewing prescribing patterns in the US from 2000-2010:
Despite a high probability of viral etiology, acute respiratory tract infections (ARTIs), such as bronchitis, pharyngitis and sinusitis, account for 75% of all antibiotics prescribed by office-based providers [9-11].
While I wasn't born in the 90's, but I was in elementary school and Jr. High in the 90's, and I remember those days of parents taking their kids in to get antibiotics for things like colds, sinus infections, and congestion. (despite most of those being viral, therefore, antibiotics have no impact)
There have been some smaller scale studies that have looked into and found what appears to be a large enough association that it could be causal
Early-onset colorectal cancer (EOCRC) has been increasing worldwide. Potential risk factors may have occurred in childhood or adolescence. We investigated the associations between early-life factors and EOCRC risk, with a particular focus on long-term or recurrent antibiotic use (LRAU) and its...
pubmed.ncbi.nlm.nih.gov
And the 90's was also the explosion of the usage of SSRI's in young people and prescribing rates for people under 18 skyrocketed. And interestingly enough, there is a gut connection there. Since that class of drugs targeted serotonin levels, and they now know that 90% of the body's serotonin is synthesized in the GI tract. Seems like it's a least a reasonable potential causal link to look into.
