> however, controlling for total calories as you suggest could be misleading, because sugar provides lots of calories but often does not reduce hunger

I don't see how could it be misleading. You trade sweat treats for fullness, and you could even add low calories side meals to balance the count. That's what a lot of diet regimes do and have been proved to work.

Controlling more parameters so that there are fewer variables between test cases being compared usually reduces the degree to which an experiment is misleading. (Ideally, one parameter would vary and "all else is held constant").

Failure to control total calories just about damns the validity of any diet study right off the bat.

Many studies measure total calories as well as sugar. The study linked above explains the correlation between the two. High sugar provides little satiety, leading to higher total caloric intake because you tend to eat the sugar in addition the other, satiating calorie sources.

You do not simply control for an additional variable when you know there is a direct link between the two. You study it as a dependent variable.

Edit: replaced "fulfillment" with "satiation". Sorry about the vagueness, I thought the meaning was pretty clear from the context.

Which is a reason why you have to control total calories to know that sugar consumption is actually a detriment to health (and at what quantities) and not just a caloric surplus.

"fulfilment" is a vague term and you're veering off the topic into a strawman argument

Yes, and here is the thing: you can't control for the total calories and vary only sugar intake. The change in sugar has to be offset by something else to keep the calories constant. So then to know whether a sugar change is responsible, we have to try different experiments with the same delta in sugar, but varying compensating substitutions.

I think you're missing the point.

It wouldn't make much sense to keep the groups isocaloric but replace the calories from sugar in one group with say, protein in another. You wouldn't be measuring the same thing any more.

The entire point of the study is comparing monosaccharides to polysaccharides and observing changes in 'health' (excuse the vague terminology). Sugar is substituted with a longer chain carbohydrate in well planned research.

> The idea is not that 'sugar is bad' or 'sugar is unhealthy', but that sugar is bad and unhealthy as it is being used in our current society.

that's just as vague as 'sugar is bad'. Sugar consumption, I would think, varies pretty widely.

This is the first I've heard that controlling for total calories would be misleading and your rationale doesn't make any sense. The inverse is misleading, if you don't control total calories then the conclusions drawn from the study don't represent the variables that were altered.

Hunger is a separate topic, you don't design diets so that people have 'the same level of hunger' between control groups because that's not easily quantifiable and irrelevant.