Updated: Aug 29, 2020
Simply put, no. Sugar does not make you fat.
I know that may sound a bit crazy, but let me tell you why it doesn't.
Firstly, in order to gain weight, you need to be eating in a caloric surplus. This is when you consume more calories than you burn off.
You could be eating lots of sugar but as long as you are not in a caloric surplus, you will not gain weight.
The one thing about sugary foods is they are high in calories. That means you don't have to eat much of those foods to hit a caloric surplus. It's much harder to hit a caloric surplus when you are consuming nutrient dense foods over consuming calorically dense foods. That is also why it's possible to gain weight when you eat healthy. It's not about the foods, it's about whether you are in a caloric surplus or caloric deficit that will determine if you lose or gain weight.
Once you are in a caloric surplus, it can go one of two ways. Either you can gain muscle or gain fat.
The type of weight gained (fat or muscle) is determined by the amounts of macronutrients (protein,carbs,fats) you consume and the physical activity that you do. For example, if you are only doing cardio, or you are not exercising at all and mainly consuming carbs and fats with very little protein in a caloric surplus, you will gain fat. This is because your body is not getting the signals it needs to get like it normally would through weightlifting. Those signals sent through weightlifting tell the body to build muscle. If you're not getting enough protein on top of that, your body can't build or maintain muscle as those are the building blocks it needs for those processes to occur. Another change from not consuming enough protein that occurs, is the loss of muscle, which unpleasantly gives you a higher body fat percentage because now that your body lost some muscle, the percentage of your body composition is different.
Fat loss, muscle gain, or living a healthy lifestyle does not have to come at the expense of giving up everything you enjoy. It's not an all or nothing approach and shouldn't be if you want to attain long lasting results. Sugar, like anything, should be consumed in moderation. Enjoy the small things, treat your body well, and have a treat here and there! A balanced lifestyle is a healthy lifestyle.