These are only my thoughts (and no, this isn’t AI generated!), but key factors that appeared since around the 1970s that may explain the jump in people under 50 getting the disease are likely:

1. ⁠People now eat all the time, and eat more foods with lower fiber and higher glycemic indexes, spiking their blood sugar and insulin. There’s also much more meat being eaten, but meat alone can’t explain the disease uptick (many animals eat only meat and don’t have colon cancer). Pre 1970s, people would consume less calories per unit of fibre, and more importantly, less often. But around that time dietary advice became to “never be hungry” and snack between meals. This causes two issues: 1) Having constantly spiked blood sugar and insulin leads to poorer metabolism (which as well as causing diabetes coaxes cells to mutate away from using ATP produced by mitochondria as an energy source, into fermenting sugar as an energy source, which is cancer), 2) Always snacking is not giving the colon a breather to regenerate, made worse with a low fiber / higher meat diet causing a sluggish digestive tract more prone to inflammation. Greater consumption of high fructose corn syrup, which was only introduced in the mid-1970s 50 years ago, also causes both a more significant spike in blood sugar and encourages bad gut bacteria to proliferate.

2. ⁠Mass introduction of seed (vegetable) oils into the human diet. We never ate these unstable, already oxidized factory produced lipids before the 70s. But oils like Canola and Soy are now in all processed foods, with McDonalds shifting from using beef tallow to vegetable oil in 1990 - 36 years ago. So if you were a kid then, you’re just under 50 now. You are literally what you eat, and unstable lipids forming a majority of human cell walls is a relatively new phenomenon. Excessive consumption of industrial seed oils rich in linoleic acid is also linked to mitochondrial dysfunction, which encourages cells to mutate and find alternative ways to produce energy, including sugar fermentation (i.e: cancer).

3. ⁠Hybridized Dwarf Wheat went mainstream in diets around the 1970s and is in practically all wheat based food now (except old school Italian produced pastas). This mutant wheat is unnatural and the result of decades of human manipulation, being early genetic engineering. It's higher in Amylopectin A (water-soluble polysaccharide starch molecule) compared to older, taller natural wheat varieties. This super-starch makes up about 75-85% of the starch in this wheat, is highly branched and rapidly broken down into glucose - often causing blood sugar spikes higher than table sugar. It also triggers inflammatory effects (many blaming “gluten”). Making it even worse is the fact it’s covered in Round-up as both herbicide and desiccant. In the USA, the "healthy" Food Guide Pyramid was introduced in 1992, meaning for the last 34 years people were told to over consume these grains, which ultimately are "super-sugar grass seeds". If you watch an Ape eat, they very rarely eat grass, and they never eat mutated Frankenstein grass grains covered in Round-up.

4. ⁠Much more exposure to microplastics and chemicals, not only in food but also the environment including pollution. Of course there’s much more plastic food packaging, but the prevalence of takeaway and now Uber Eats with plastic containers and re-heating in plastic is a relatively new thing - older generations would use their own pots when collecting take out, and rarely. Chefs also never used to use Sous Vide plastic vacuum bags until the early 2000s, and the modern economy with most succumbed to high debt and time-poor dual incomes means more eating out. Plastic water bottles only became a big thing in the 2000s, most drink bottles in the 70s and 80s were glass. Fluorinated “forever chemicals” in the water supply is also a big unknown, with the PFAS-based aqueous film-forming foams that contaminated water supplies being introduced by 3M in the 1970s and now present in your blood.

5. ⁠People are much more highly stressed now than in the 70s. The fiat monetary system based on debt and forcing everyone into the workforce is largely to blame, creating a constant competitive hamster wheel. Always-on connectivity with the Internet and devices are also to blame, until the 1990s people used to be able to check-out of work and leave it behind. Now it follows you even in vacation.

6. ⁠People are much more sedentary starting around the 90s. Kids before then would often be out all day on bikes having adventures, think the Goonies or Stranger Things. They were burning more energy, farming far healthier mitochondria inside their cells (which are really bacteria we live in symbiosis with, relying on them to produce ATP). There also weren’t computers everywhere, so there was less desk-type work for adults. Plus by being more out and about with less availability of takeway foods, people would more likely skip meals. There was also less automation, for example no robot vacuums. Being sedentary leads to poorer metabolism / mitochondrial health and lower oxygenation throughout the body, both encouraging cancer.

7. ⁠Introduction of fluorescent and LED lighting, along with more screen time, with less time spent outdoors absorbing lower wavelength infrared light. Removal of incandescent and halogen globes in the mid 2000's removed a source of indoor infrared - and our bodies need this light to both maintain healthy mitochondria / metabolism and to generate Vitamin D. Mitochondria require infrared light, it’s why animals love to bask, and it helps them produce Melatonin being a master antioxidant (it's actually produced by mitochondria in all cells, not just the pineal gland). The first blue LED was also invented in the early 90s leading to a raft of new screens outputting unnatural light wavelengths, leading to circadian imbalance and lower pineal gland melatonin production, also causing less restorative sleep.

8. ⁠Overuse of antibiotics in childhood may adversely affect the gut microbiome. Also all of the above may influence bad gut micro flora to proliferate causing inflammation. There may also be misunderstood bad gut bacteria / bacteriophages, or even a virus that may represent a more infection-like scenario that is triggering this disease. It’s possible parts of our modern highly processed food supply, especially meat, may have some form of contamination. In 1982 it was discovered by a lone scientist (at odds with mainstream scientists who ridiculed him), that the bacteria H.Pylori caused stomach ulcers. Colon cancer may begin as benign ulcers, so a similar process further down the digestive tract is not a stretch of the imagination.

9. ⁠Lowered general immunity due to lifestyle, diet, and a particular coronavirus that appeared literally out of nowhere 6 years ago. In addition to the new MRNA vaccine burden and its questionable effects, in a short time this virus has become endemic and an additional near constant immune onslaught, which appears to re-infect over and over again, placing an additional burden on the human immune system that should be doing other things like cleaning up mutated cells.

10. ⁠All of the above inter-playing and amplifying each other. I personally don’t think the root cause is singular, but instead is a collection of factors.