I lost 10kg in 5/6 months this summer due to things like running for 30min 6 days a week, not eating carbs at night and never eating more than 1000 calories a day. My nutritionist gave me a meal plan and I stopped running and started strenght training instead (with 1,5 dumbbells), I'll admit I don't fully commit to the meal plan especially the quantities of rice/pasta. Now I always eat between 1300-1600 calories a day, I weight 42kg and heigh is 167cm. I'm scared to stop exercising bc the reason I started it was so I could lose belly fat bc i've always been skinny fat and wanted to stop being that and be comfortable in a bikini (which I still am not). I also love exercising, it makes me feel good, but I can't control myself, or add more calories than usual just bc of it. I have an eating disorder, and refuse to eat anything considered not healthy or anything that's refined like cookies, white rice or white bread (although sometimes I have to do it but feel awful afterwards). I dont know I know I need to gain weight but dont really want to if it means more belly fat, how do I gain weight the right way? And how much do you think I should be eating for each meal? I'm 18 and a girl
You should start to run again, because that's the way you can make your body feel that you need to eat a lot. It's easier to eat 2000 kcal or 3000 kcal per day and get to a surplus of a few hundred kcal per day when you're running a lot, compared to not burning a lot of energy. It looks like you can easily get to a surplus energy intake when you need to eat a lot less, but the human body doesn't work that way.
Our metabolism evolved hundreds of millions years ago, it's a very robust system. If you run a lot then because animals only exert themselves for survival (e.g. getting to food), mechanisms will kick in that make your body better adapted to this situation, so running will become easier. For most people this will mean that they'll lose weight, but if you are underweight, you'll gain weight (provided that you're not overdoing it, you must avoid overtraining).
In contrast, our brains only evolved a few hundred thousand years ago, it's not yet fully optimized, we're prone to depression and other mental issues. So, what you want to do is rely on the more primitive but robust mechanisms instead of your brain when it comes to gaining weight. Attempting to micromanage your diet when your body should do that by itself isn't a good idea. It's better to rely on the more primitive feeling like hunger and make yourself hungry by exercising a lot and then eat to make that hungry feeling go away.
The diet should consist of whole grains, brown rice, a lot of vegetables and fruits, moderate amounts of protein and moderate amounts of fats. The total calorie intake should be large enough so that you don't feel hungry and that then includes days when you've been doing heavy exercise. The amount of calories you should be eating should be at least 2000 Kcal per day but it can be a lot more.
E.g. I'm just as tall as you are and I weigh 54 kg. I eat about 4000 Kcal per day, I eat 500 grams of whole grain bread and 250 grams (weighed uncooked) brown rice, or whole grain pasta or 1 kg of potatoes a day. I eat 500 grams of vegetables a day. I only eat a small amount of meat and add a small amount of fats to my food. Now being as big as you are, this shows that your stomach is not too small to hold large amounts of foods. But you need to gradually increase the quantities of food to get your body adapted to digest large amounts of food.
When you're still struggling to eat a large quantities, you should eat larger amounts of meat and add more fat, later when you are able to eat larger amounts of food you'll be able to get enough proteins and other nutrients from vegetables and grains and then you can reduce the amount of meat. You can reduce the amount of fat if you are able to get enough energy from carbs.