Though similar decline is reflected at a couple other online areas [1] [2] I am however not going to research and quantify that ... besides I don't trust the big food industry to provide accurate figures, I'd only confidently trust a totally independent facility that confirmed overall sugar and easy to digest carbohydrate levels in each food item and average consumption by the population.
Sugars like sucrose and HFCS rather than regular corn syrup, yield 50% and >42% fructose respectively. It's consumption in great quantity does not seem to have a major impact on some people, but certainly others are prone to the vast amount of fructose consumed. Harvard iirc showed how the extra fructose in diet corresponded to longer villi in the gut.
Obviously there's other factors at play, but excess fructose consumption is nonetheless an obvious change in diet to what those earlier than 60 or 70 years ago.
[1] https://www.healthyfoodamerica.org/sugartoolkit_overview_ori...
[2] https://www.researchgate.net/figure/Sugar-consumption-in-the...
I'm implying excess sugar consumption, including HFCS, is not the cause of the obesity epidemic. No one's telling you to eat it, though.
I for one, noted first hand the very stark difference cutting down the fructose had, not just on weight, but how it modified my mood and appetite. In actual fact the one problem I had with my little self experiment was my diet got worse balance wise. There was no placebo effect to account for IMO, since trying for years on actively planning time to be very active did not help much, though my muscles were better for it, I had expected a mere change in removing fructose to be on a time scale of at best 10 months, and expected more likely if it worked at all, after a year I might be lucky enough to lose 10 kg (approx 20 pounds) ... instead on starting the low fructose diet, my mood notably improved in a week or so (I didn't think I had a mood issue - I am what I am, so that was unexpected,) and I didn't shed 10 kg but 25 kg in two or three months (I no longer recall the exact time frame) ... and while I did that I was no longer push bike riding where I might easily clock 100 km (60 miles) in a day but still moderately active but not that active. Seemed clear to me though a few people would not respond the same, but since I'm not unique, many would also fare similarly as well. The only issue was the tedious nature of introducing and staying true to ensuring that sugar consumed was far more glucose than what broke down into fructose, even though I still ate a small amount of processed food - most sugar was fortunately by way of hot drinks consumed during the day.
To say it was actually something else in my case, equates to blaming eating a pie, a couple boiled whole potatoes or same ration of pumpkin pieces, 3 cups of milk per day for my weight problem back in my 20s ... I really wasn't eating very much, though sugar was powering my days.
I think reducing excess sugar consumption is necessary but not sufficient to get lean for some obese individuals like myself.
When I started keto 7 years ago I lost 100lbs. Then I gained it all back - staying pretty strict keto the entire time. I haven't had what you'd call "processed food" or "sugary food" in nearly a decade if you exclude a small % of keto-style things like dark chocolate (85%).
Now back down 45-50lbs (depends on how you count) and hopefully going to continue. But this time I cut out protein, too. It could be that both carbs and protein raise insulin enough to cause obesity in some people. Or maybe seed oils in even the tiniest doses. Those are my two main hypotheses: https://exfatloss.substack.com/p/hypotheses
There will of course be a small percentage of people who carry more fat, for different reasons entirely, not directly related to diet or exercise even.
Interesting experiment you're running. Funny thing, one of those years where I never lost much weight push bike riding and other ideas, I landed a 15kg box of dark chocolate buttons - unintentional but I indulged and started bagging up about 3/4 to a full cup in a bag to take with me for the day's travel ... by end of box I'd lost a bit over a kilo (2 pounds) which seemed odd to me.
[1] https://www.ncbi.nlm.nih.gov/books/NBK576428/#_article-14058...
However there's a lot more than that going on, iirc didn't Michael Moore produce a doco on some of the tricks big fast food industry use to entice more food consumption.
I don't think there's just one box and everyone is the same, but in my 20s due to an accident I gained a lot of weight where I needed suspenders to keep my jeans and trousers up, and once I was well enough I first walked a few mile every day and eventually using a push bike to travel to my nearest town for further studies about 30 miles (50km) away. Sure those trips moved from taking around 4 hours down to just over 2 and peddled near everywhere at that point, I still had most of that excess fat around the gut. Even after I stopped riding a bike, it was about the same but I still did quite a lot of manual work at that point and ... I tried that experiment more or less they'd done on rats, I used glucose instead of sucrose and maybe it would help ... in a mere matter of weeks instead of months the fat just fell away, and even before much had fell away I'd felt so much better.