Eating because you really need to eat to fuel your body or because your stomach is complaining. Contrast with mouth hungry. Many people who have food available to them constantly have difficulty identifying true stomach hunger, and this is one of the reasons why obesity has become a widespread problem.
Some situations mask the feeling of stomach hunger. Most people have experienced the situation of being too busy and absorbed in some task or hobby to notice that they need to eat. Anxiety can cause stomach feelings that can be mistaken for hunger. And several types of medications (painkillers and anti-convulsants, for example) can mask the signals of hunger. Low blood sugar, causing jitters, light-headedness, or crankiness, can be the next sign of needing to eat if someone misses feeling their earlier stomach hunger signals.
However, many dieters say that they tend to overeat if they wait until feeling something they identify as stomach hunger. Being able to identify when you've eaten enough is just as important as being able to identify when you are stomach hungry rather than just eating for some mental reason. This is particularly necessary because there is a delay of about 20 minutes between having eaten enough and the time when the food is processed enough to increase the blood sugar, allowing a person to become aware of having eaten enough; therefore stopping when you feel completely full generally means that you have continued eating for a while after the amount that would really have sufficed.