I picked up a link to this paper from an image of a table, somewhere on Tinternet. I didn't realise which paper it was. It was really interesting from the metabolic point of view and I kept looking through the results section to find the post-prandial metabolic effect of ultra-processed foods vs unprocessed foods. You know, the effect which might determine where the calories from a given food might end up, either available for metabolism versus lost in to adipocytes.
Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake
This is from the introduction
"Ultra-processed foods may facilitate overeating and the development of obesity (Poti et al., 2017) because they are typically high in calories, salt, sugar, and fat (Poti et al., 2015) and have been suggested to be engineered to have supernormal appetitive properties (Kessler, 2009; Moss, 2013; Moubarac, 2015; Schatzker, 2015). Furthermore, ultra-processed foods are theorized to disrupt gut-brain signaling and may influence food reinforcement and overall intake via mechanisms distinct from the palatability or energy density of the food (Small and DiFeliceantonio, 2019)"
What this is saying is that making foods high in calories + "supernormal appetitive properties" makes you eat more, so you become fat. And that they alter gut brain signalling to increase "reinforcement" and so increase intake. You have to put the excess calories somewhere so you get fat.
Supernormal appetitive properties. Energy density. Reinforcement.
But the bottom line is that highly processed foods do produce steady weight gain over two weeks and low processed foods do the opposite.
What we need to know is how a given food affects both the acute and chronic metabolic response, especially insulin levels and signalling. That's not going to come from the psychobabblers.
Luckily there are groups with an interest in the metabolic effects of food, rather than being lost in un-Rewarding theories of reinforcement. Like this group:
Does food insulin index in the context of mixed meals affect postprandial metabolic responses and appetite in obese adolescents with insulin resistance? A randomised cross-over trial
They compared two meals with the same low glycaemic index (GI) but differing insulin secretion indices (Insulin index, II). Both meals had very similar macros and they look suspiciously like processed vs unprocessed. Insulin (and glucose) were higher after the high II meals:
The low II meals generated less hunger in the post prandial period. I'm not sure what hunger has to do with weight gain, I get the impression from people like Hall et al that calorie intake controls weight gain. Hunger is something else, will-power dependent maybe.
The second study has some problems too. The low II food did not taste as good as the high II food. So Rewarders have a lifeline here. And if you are making a marketable commodity to be labelled as "food", anything you can do to increase its palatability is going to improve sales. If palatability should turn out to be intrinsically linked to a food's II then you are set to drive hunger combined with those increased sales. Win-win for the shareholders but not so much for the consumers. No one wants to be fat. Equally, no one can tolerate being hungry...
The second problem is that there was no increase in food intake for the high II group during the end-of-study buffet. An increase in food intake here would have been nice, to corroborate the increased hunger. But that meal was a free choice buffet being offered to people who were already obese, so poor food choices may well have over-ridden the differences in experimental meal induced hunger. Back in the days of better designed studies the post-insulin test meal was a uniform soup-like liquid, consumed via a straw through a screen so there were no visual or food choice cues to influence food intake. A pity, but there you go.
Insulin makes you hungry. Not directly, but by diverting calories in to storage. You lose those calories so your brain gets hungry. Making you fat is how insulin makes you hungry. Pure CICO but the calories-out go in to your adipocytes...