Does body fat only come from caloric surpluses? Is it possible to be in a calorie surplus and not gain any fat? Do carbs and sugar increase body fat and if so how?
The only way to gain boday fat is through being in a surplus, if you eat more food then you need for lets say 24 hours you will gain fat
but lets say you are glucose and glycogen depleted and eat in a surplus of carbs and sugar you will mostly store them as glucose and glycogen altho it dose not mean they cant be stored as fat
either way calories are energy if your body dose not store the energy as body fat it will store it as gluose or glycogen
These may help but there are plenty of articles that explain the biology and science behind fat stores.
https://www.health.harvard.edu/staying-healthy/why-people-become-overweight
If there’s room in your glycogen stores, surplus can go there first. This is a shorter term energy storage system.
The body may also use extra calories for heat or excess movement or whatever. Then it’s not really a surplus, but the point is, your calorie expenditure can change based on your intake.
The body can convert carbs and protein into fat for storage. The process is less efficient for protein so only like 70% of protein calories will be used for energy.
To simply answer your questions how I believe you mean them:Yes, an increase in body fat comes only from a caloric surplus. No, it is not possible to be in a caloric surplus and not gain any weight(how many calories it takes for each person to be in a surplus varies, but if you are in a surplus you will gain weight). Carbs and sugar contribute to increased body fat only if you are in a caloric surplus.
Understanding how weight gain/weight loss work vs true health is quite different. For example, you can eat poor quality food(ex. Mcdonalds) but if you eat a reduced amount and maintain a caloric deficit you will still lose weight. In this scenario your eating habits would still be unhealthy and would likely have negative effects in the long term. On the other hand, you can eat tons of healthy foods(fruits,veggies,legumes,complex carbs,etc) and if you reach a caloric surplus you will still gain weight. In this example you are still “healthy” but could be a heavier weight.“Carbs” are a controversial topic in the world of nutrition but generally are fine in moderation especially when they are complex(ex. whole wheat bread rather than white bread). Sugar is also controversial but avoiding added sugar is generally a good rule. Sugar from fruits and other natural sources is largely debated but still has many health benefits and is thus a better choice than added sugars.
Short answer - calories in vs calories out is the most important for fat loss and fat gain. However you can absolutely gain/store fat by not sleeping and or having large cortisol spikes from being stressed. There’s also something called de novo lipogenisis which means “new fat”. If you over load your body with simple carbs your liver can only process so much at a time, so if you have too much your body will store those extra carbs you can’t process into fat.
“Calories in calories out” is one of the biggest factors but is an incredibly blunt simplification.
Don’t listen to anyone telling you it’s the ONLY factor. Really stupid take.
There are a variety of metabolic/other hormones involved that also affect body compostion, that can be altered by diet, exercise intensity, sleep quality, sunlight, testosterone levels, that control where fat may be stored in the body, and for which reasons.
Non-alcoholic fatty liver disease, brought on by a high-glycemic diet full of refined carbs and sugar, is a prime example.