After reading this interesting blog about some studies with fructose, it seems very likely to me that fructose DOES contribute to obesity if one consumes enough of it along with a high fat diet. However, if one consumes calories from fructose while eating a low fat diet then it does not seem to promote obesity. So the rules seem to be:
If you are eating a high fat diet--avoid fructose.
If you are eating a low fat diet--allow fructose.
It makes it very easy to follow the rules if you get absolute about the consumption of fructose. Fructose seems to be beneficial in some contexts. I would not jump to the conclusion that it is generally bad or toxic. So this is where the whole fructose debate comes to a head. How much fructose is too much for the amount of fat in our diet?
Here is what I propose. If one is wanting to lose weight, then the first thing to do is to practice TRE (time restricted eating). It is not necessary to determine the amount of fat in your diet. Simply restrict your eating to two or three one hour windows per day. At the beginning avoid fruit, fruit juice, sweetened sodas, and dessert type foods. The object is to reduce the MAJOR sources of fructose. Continue eating foods that may have incidental amounts of fructose such as canned vegetables, condiments, or breads. Monitor your weight.
If you feel confident that you are losing weight, then add a piece of fruit or a small cup of juice or soda to your meal and continue monitoring your weight. If you feel you are still losing weight, you can increase the amount of fructose foods gradually. If you stop losing weight, then you should stop adding fructose foods as it does not seem to be compatible with your diet.
My guess is that ice cream and chocolate candy and other foods high in fat and sugar are probably least obesogenic if eaten seldom unless one is eating a low fat diet. If eating a low fat diet then some ice cream or chocolate candy will probably not cause any appreciable weight gain.
Here are some questions which seem more difficult to answer:
Is it still obesogenic to eat a low fat high fructose meal on the same days you eat high fat low fructose meals?
Is it still obesogenic to eat a low fat high fructose food/dessert after finishing a high fat low fructose meal?
Is it still obesogenic to eat low fat high fructose meals on alternating days with high fat low fructose meals?
You can follow my TRE experiment (reduced fructose) at Jimmy Moore's Livin' La Vida Low Carb forum.