Let's start with the most important thing:
weight changes aren't caused by any one nutrient, but by the overall calorie balance.

If you eat more than you burn, you gain weight.

If you eat less, you lose weight.

But KFZ influences how exactly this happens: through fat, muscle, or water.

1. How much fat do you need?

Fats aren't the enemy. They're essential for hormones, skin, and the brain.

Minimum for health:
approximately 0.8 - 1 g of fat per 1 kg of body weight.

If you go below that, problems arise: hormones, energy, and well-being.

To avoid fat gain, it's important not to exceed your overall calorie intake.
You can eat even more fat, but if your calories are within the normal range, your weight won't increase.

For active fat gain to occur, one of two things usually happens:

either a significant calorie surplus
or a high fat intake and a high carbohydrate intake (the most dangerous combination)

2. Carbohydrates - when they're a hindrance and when they're not

Carbohydrates themselves don't make you fat.

They provide energy. The problem arises when:

there are too many of them
and not enough exercise

Then the excess energy is stored.

For balance:

When losing weight, you can slightly reduce carbohydrates
When maintaining weight, maintain a moderate level
When gaining, increase them

3. Protein is the foundation of fitness

Protein is what helps:

preserve muscle
avoid overeating
look toned

Optimal:
1.5 - 2 g of protein per 1 kg of body weight

4. Example of a calorie-fat-carbohydrate ratio for weight maintenance

If you don't want to gain weight:

Protein: 1.5 - 2 g/kg
Fat: 0.8 - 1 g/kg
The rest is carbohydrates

5. When does fat gain begin?

Fat accumulation begins when:

there is a regular calorie surplus
lack of activity
a lot of "delicious, dense foods" (fats and carbohydrates combined)

For example:
fast food, sweets, and fatty foods are the fastest path to weight gain.

Conclusion

There's no "magic" amount of fat or carbs that will make you gain weight.

There are:

overall calorie balance
and your habits

If you don't want to gain weight, keep your calories under control.
If you want to lose weight, create a slight deficit, but don't cut fat too much.

Balance isn't a strict diet, but a system you can maintain for the long term.