[bombcar]

A tablespoon of mayonnaise is 90 calories.

A tablespoon of the most HFCS sweetened ketchup is 20 calories.

It may be a win on taste but I'm not sure it's a win on calorie reduction. I do love some mayonnaise fries, tho.

[outime]

But if we go one level deeper, fat does fill you up much better than simple carbs like HFCS. In fact, HFCS will create more appetite (more than even plain sugar) down the road which at the end will make you eat more - and probably even of the same kind. Therefore, it's not very clear to me it's a win in calorie reduction either.