> And does this greater mass of fat, which itself is a hormonally active organ, affect the body in a way that results in illness and further weight gain?
These are very good questions. Here's what I know (caveat it may not be complete, but I am confident it is accurate):
1: Hmm, chronically high insulin levels is caused by chronically eating too much. Beef spikes insulin just as much as table sugar (http://ajcn.nutrition.org/content/66/5/1264.full.pdf#page=1&...). So I would say the problem of "chronically high insulin levels" is a problem of eating too much food, not too much sugar.
2: This is a hugely interesting area of thinking for me. Which fat though? White or brown adipose tissue? Brown fat is darker in colour due to it's huge cellular density of mitochondria when compared to white adipose tissue. It's essential fat-buringing fat, and plays a role in regulating temperature. It basically burns fat to warm us up when we're cold. This is why Michael Phelps can eat 10 million calories a day. 6 hours a day in water requires allocating a LOT of calories to maintain core body temp. We have learned SO much about fat tissue recently, but I don't think we have all the answers yet.
I noticed this red-flag from the thought-experiment:
> We know the liver will turn some of this fructose into fat and if the fructose is delivered quickly
Yep, but less than 1% is converted into fat (http://www.nutritionandmetabolism.com/content/9/1/89), and this is in a state of caloric surplus. The thought-experiment method is for the subjects to eat calories to match their TDEE (Total Daily Energy Expenditure), so it's much more likely that none of this fructose will be converted into fat, it's more likely to completely converted into glucose by the liver.
> Let’s assume two things for the sake of argument. the sugar in A’s diet causes A to become insulin resistant. And second, insulin works to put fat in fat tissue.
I would say both assumptions are fallacious. Eating @ TDEE means 100% of the food energy is used up, and fat cannot be made from nothing. More sugar in this case does not cause insulin resistance, beef stimulates insulin release into the blood just as much as sugar does, so one can't isolate a single macronutrient like that. Also, the "insulin works to put fat in fat tissue" is misleading at best and completely wrong at worst, depending on how you interpret it. Insulin works to move nutrients into cells. More insulin in the blood is a signal there is food calories available, so insulin also stops fat cells from releasing their fat. This makes total sense; why dip into your savings when you just got a fist full of cash? The point where your body transitions towards fat storage is the point where your energy intake exceed energy expenditure; again just simply eating less solves this.
My statements are all for average healthy people. I totally agree metabolic-syndromes like diabetes should be treated differently. But the VAST majority of people are fat because they sustain consuming more energy than they use. The micro-variables like how stressed you are (and therefor how much cortisol hormone is present) matter, but nothing gets diet-induced hormones working as they should better (in healthy people) by just eating food-energy (whatever the macros) to match your activity over the long run.