Researchers from the University of Aberdeen and the University of Chinese Academy of Sciences have discovered that mice fed high sugar diets don't gain weight but mice fed lots of fat do. Of course, there are also studies that show that in humans that is not so and sugar makes you - if you are human - quite fat quite often.
So perhaps this is testimony to how the mouse animal model doesn't always work to model a human body. Or perhaps testimony to the dearth of true knowledge on metabolism and nutrition.
Whatever is behind this, I find this finding interesting and worthy of attention.
Sources
Mice Can Eat Sugar Without Weight Gain, But The Jury Is Out When It Comes to Humans
Mike McRae, Science Alert, 18 July 2018
Intake of sugar-sweetened beverages and weight gain: a systematic review
Vasanti S Malik, Matthias B Schulze and Frank B Hu, The American Journal of Clinical Nutrition, August 2006