What exactly do people mean when they say that they lost weight from stress and did they not have an appetite to eat?

When some people are under stress they may lose their appetite completely, or they may not eat proper meals and just pick here and there. It isn't enough to sustain their body and they lose weight. If a person is inclined to be thin, they could be eating but between their thyroid and adrenal glands working overtime from the stress they may lose weight even though they eat like a mac truck driver.