But why are you so hungry?
Let's be clear: We're not talking about actual starvation, or hunger as a pervasive global and social issue. We're talking about hunger in typically healthy people with comfortable access to food — the hunger that arises from the physiological need for nutrients to survive. Hormones and the nervous system regulate hunger and eating habits. But how the heck do we recognize when we want to eat, even when we actually don't need food?
Richard Stevenson is a professor of psychology at Macquarie University in Sydney, Australia, where he studies human eating behavior. He says that hunger is by no means a universally identifiable sensation. "Unlike fullness, which there is no mistaking, hunger is very varied," he writes in an email. "It is not a consistent sensation across people, and it has been claimed that feeling stressed can be confused with it."
Even some of the biological functions some people associate with hunger — a growling stomach, for instance — aren't entirely foolproof cues. "Many people do not report stomach sensations when asked to describe what being hungry is like," Stevenson says. Indeed, reports show that people cite headaches, weakness, mouthwatering and other nonstomach-related sensations as signs of hunger. Stevenson has also done research that indicates feelings of hunger and fullness are influenced by a myriad of factors, including genetic and psychological differences like depression, anxiety and eating disorders.
Then there's a really big factor: Our environment can easily convince us into thinking it's time to eat, whether we're hungry or not.
"Seeing, smelling or thinking about food," says Stevenson, will trick us into believing that our stomach is crying out for nutrients. "That is why food ads work so well," he says. And that affects not just appetite, but how much food we actually consume. A 2009 study showed that both children and adults eat more snacks after exposure to food advertising, and a 2016 review found that food ads significantly increase unhealthy food intake in children. In fact, researchers coined the term "hedonic hunger" to describe the drive for food consumption unrelated to the need for calories.
This phenomenon also might give us a clue to another mystery of hunger: How can we claim ourselves ravenous, only to find — after time passes or a distraction interrupts us — that the hunger has passed?
Stevenson says this waning hunger could be related to the idea that our appetite isn't always activated by an actual need for calories. The elusive hunger pangs may occur because "the thing that triggered the hunger feeling has passed," he says, or because a regular eating prompt has flown by. "Time is also a potent cue to eat," he says. "If you usually eat at midday and you miss this, you will feel hungry if you notice the time."
So, what's the trick to deciding whether you're truly hungry? Is there a scientific method for being able to push away the bowl of chips you don't need?
"In a word, no," says Stevenson. "Most of our biological machinery is geared to make us eat when we see food or things that remind us of food." That was terrific for our ancient ancestors, when humans had to spend a lot of time searching for energy sources. But it might leave us at disadvantage when surrounded by a huge spread of snacks right after a filling meal.