Carbohydrates have been massively demonised in the dieting industry. Majority of it all has been taken weigh out of context. Just by eating a single piece of Carb will not cause fat gain. Over consumption causes weight gain.
The reason people lose weight after reducing Carbs is because they have created a calorie deficit!
The main role for Carbohydrates is to provide energy. If the body has all three Macronutrients (Fat, Carbs, Protein) available it will always burn Carbs first. Your body will always be turning over protein, using fat for cellular function and then using Carbs for energy.
Depending on what you are doing the ratios of your body using the three Macronutrients is not set in stone. If the stimulus changes (exercise) your body will change things around, may use fat for energy depending on the carbohydrate stores and the length of the exercise duration.
You do not need Carbohydrates to live, however it is not advisable to reduce your Carb intake this low. Your body likes to run on this energy source and performs its best with a good carb intake. Having said this, because it is none essential to the body you can easily manipulate it for a short/medium term goals i.e reduce pasta portions or swop normal rice for cauliflower rice. For long term and life long goals you want to find a good balance where you have carbohydrates within your diet and you feel great.
Generally speaking whole grain Carbohydrate sources are better than white Carb sources. This is because you are benefiting from them being more natural and less treated than white carb sources. They are typically higher in vitamins, minerals and fibre due to being less treated. However if you prefer white rice to brown rice then that one portion of white rice is not going to harm you. Just make sure the rest of your choices are good ones!
Moderation and good wholesome choices is the key!