The answer would surprise you. It is yes. Both are different. If you lose weight, it does mean that you are also losing fat. It is true the other way round also; if you are losing fat does not mean that you are losing weight.
You body gets energy to function from the food you eat. This energy is counted in terms of calories, but that you already know. Now, if you eat more than required then the excess calories are stored in your body in the form of fat. Therefore, if you do not eat enough food to last you for the day then you will end up losing weight. At the same time, you also will lose energy. Now, you might be thinking that to make up for the energy deficiency, your body will use up the stored fat. However, it is not so. The body uses up proteins as well as carbohydrates instead of the fat.
Where do these carbohydrates and proteins come from? Well, they come from your muscles. So, now while you are not losing any fat, you are actually losing whatever little muscle mass you had; time to say your goodbyes to that beautiful toned look. In addition to this, all of this also causes your metabolism to slow down. This results in slow or even no burning of fat. Once your metabolism slows down, your body is adjusted to the new lifestyle of getting less energy. As a result, whatever initial weight loss you had experienced (because of the muscle loss), will also stop and you will no longer lose any weight.
You should know that the weight that you initially lost was mainly water weight. You will easily gain this weight back, but when you gain back, it will be in fat form. The reason the initial weight loss is water weight is because the carbohydrate and proteins that you lost initially actually retain water in their cells.
Now, if you combine exercise with starving yourself, you cannot get any dumber. The reason is that you will burn more calories through exercise and therefore your body will need more energy, which it is obviously not getting because of your less food intake. Now you know where the energy will come from. This way your body will go into starvation mode, in which it keeps storing all the food you eat in the fat form because it is unsure about the next time you will feed it.
Therefore, the smart thing to do is to get off that starvation diet and treat yourself with a balanced diet consisting of all essential nutrients. Combine that with exercises that will rev up your metabolism and increase your oxygen needs. That is the smart way of staying fit and healthy.