You would think eating less would result in less stomach fat. Unfortunately, this isn't necessarily so. Eating less food than your body needs results in malnutrition. This can be in the form of vitamin deficiencies, protein deficiency and/or carbohydrate deficiency. Ultimately, this leads to starvation of the body. There are many pictures of people on TV literally starving with a round tummy. This is called kwashiorkor.
Your body needs a wide variety of nutrients to keep it functioning. Just like your car, if you don't fill up every once in awhile, you won't be going anywhere. Your body works in a similar manner. If we don't eat enough, stored fat can't keep the body functioning. To lose weight, you do need to cut calories and/or increase activity. You need to continue to eat enough food to support your body's functions and stay healthy. Under-eating means you are starving the various parts of your body and they'll eventually quit on you.
Eating less than your body needs causes levels of cortisol to rise. This stress hormone causes the body to hold on to every morsel of fuel that comes its way. The best place to store those morsels is in the abdomen. The less you eat, the more your body thinks it's starving, so like a small child refusing to give up his favorite toy, your body isn't going to give up any fat stores until it absolutely has to. That means under-eating isn't going to eliminate stomach fat until there isn't enough muscle to consume.
Undereating actually causes your body to consume muscle tissue to provide enough energy to keep the body going. By undereating, you lose muscle and muscle definition due to the muscles being cannibalized. Kwashiorkor is primarily a lack of protein in the diet. One of the symptoms is the protruding belly. It isn't actually fat, but fluid leaking from all the cells in the body into the abdominal cavity. This is a severe form of undereating and is rare in the U.S., although many people may suffer from different degrees of malnutrition from not eating enough.
If your body isn't getting enough food, you are going to be tired and your stomach growling and cramping may disrupt your sleep. Building and repairing muscle takes place during sleep, which can't happen when there isn't enough food to work with. You're at risk for kidney failure, heart attack and even death. You will also suffer from mood swings and generally not feel well. Eating enough to supply your body with enough fuel will actually help you to lose weight. Adding exercise will help you lose that stomach fat. You'll feel a lot better, too.