It's no surprise

Hunger can be triggered not just by our need for food, but by the sight and smell of it

Even just thinking about food can stimulate food-seeking behavior

When we're hungry

our body responds in a number of ways

When you're hungry you often feel your stomach rumbling

After a couple of hours without food

the organ begins contracting to push whatever food remains into the intestines

This rumbling is called 'boborygmus

When food is lacking

cells in the stomach and intestine will also produce ghrelin

a hormone that produces feelings of hunger

At the same time levels of leptin

an appetite-suppressing hormone produced by fat cells, will go down

Ghrelin communicates with the hypothalamus in the brain

which regulates our basic body functions

The vagus nerve sends signals to the brain about how full or empty our stomach is

as well as relaying the amount of nutrients in our intestines

Neurotransmitters, such as Neuropeptide Y are released

sending messages to various parts of the brain in order to stimulate our appetite

Key nutrients in your blood, such as glucose, amino acids and fatty acids

will be at their lowest when you are hungry

This can have a big effect on the brain

An empty stomach increases your impulsiveness and makes it harder for you to make long-term decisions

You might also get 'hangry'

where a lack of food leads to you feeling irritable

Carbs break down into glucose, which is required to make your brain function properly

When blood glucose levels are low

our bodies perceive we are in a life-threatening situation

The brain starts sending messages to our organs and glands to increase blood sugar levels

One of these, the adrenal gland, releases the stress hormones cortisol and adrenaline

triggering our 'fight or flight' response

All these body responses are triggered by an actual need for food

So why do we desire food like this even when we're not hungry

It's because when we see food

greater amounts of Ghrelin will be released even if we recently ate

Our ancestors might have gone days without food while hunting and gathering

Having his hormone stimulate our appetite whenever we spotted a food source kept our species alive

That of course doesn't apply today

and the hormone has been linked to obesity problems

where someone feels hungry even if they don't actually need to eat

When we do crave foods, it's usually the fatty, sugary kind

This is because this type of food releases opioids into our bloodstream

which generate feelings of pleasure and mild euphoria

The pleasure and reward we receive from satisfying our food cravings

are simply milder versions of what drug addicts experience when they get high