You lose weight by consuming a calorie deficit, meaning burning more calories then you consume. Running increase those calories burned. It is a bad idea to increase your physical exercise and go on a diet at the same time. When you are a runner, you need extra energy and nutrients, and you are more likely to get ill or injured by trying to restrict what you eat while doing so.

Running allows you to lose unwanted fat in 3 ways. First, you’ll burn more energy while you are running, about 100 calories for every mile you run. Second, you will raise the basic metabolic rate, which means you burn more energy even if you aren’t doing exercises. This impact is most obvious if you run no less than 4 times a week for at least half an hour. Third, you are going to improve your quantity of lean muscle mass, which burns more calories.
Your whole body has a quantity of sources for energy, which includes glycogen (that is stored in your muscles and round your liver), protein and fat. Fat is an efficient way to store energy, but it can only be translated back to energy fairly slowly. When you run at high stages of exertion, the body needs a lot of energy speedily, and uses glycogen, the most obtainable supply of energy. Only a modest proportion of the energy will come directly from fats. When you run slower, your body does not need to ask the most accessible energy stores, and a higher percentage of the energy you have comes from fat.