The links between our brains and our bellies are many and varied, as a new book explores - but is it true that having a sweet tooth make us kinder? By Sophie Morris

book cover of Why You East What You Eat, by Rachel Herz. Blue with icing covered donuts.

If you’re a liberal user of hot sauce you may be what’s called a benign masochist

In 2013, there was an uproar over a new Dairy Milk bar. Unhappy eaters complained that the popular Cadbury’s bar, which had been reshaped into more rounded pieces, was too sickly and sugary compared with the original. But the manufacturer insisted it hadn’t changed the recipe one bit. Were the customers making it up? Most likely, they were genuinely experiencing this new bar as sweeter, because the way our brains interact with food, and the act of eating it, is incredibly complex. We already know that our relationship with food is far more than a matter of taste and hunger, but the growing field of neurogastronomy can show how fluctuations as subtle as the shape of food can alter our experience of it.

It can also teach us how to tackle some of the eating habits that are making us ill.

In a new book, the neuroscientist Rachel Herz unpicks the links between our brains and our bellies. Why You Eat What You Eat, a Freakonomics for the foodie generation, reveals not only how many aspects of psychology shape our relationship with food, but how food can also shape our relationships with each other.

Why eating sweets makes us kinder Having a sweet tooth is not an empty phrase. Some of us are more sensitive to sweet foods than others, and for these people sweet food tastes even sweeter. This is underpinned by genetics, and those who are less sensitive to the taste of sweet food end up eating more of it, and may develop related weight and health problems. On the upside, a number of studies show that eating sweet foods make us nice people. This is because if we like sweet food, eating it gives us pleasure and leaves us in a great mood, and we sprinkle some of that happiness on those around us.

Why bitter food lovers might be psychopaths The intensity with which we taste bitterness - foods such as chicory, black coffee, and strong ales - depends on a gene variant. We fall into three categories: supertasters, who taste all bitter foods very strongly; non-tasters, who often love these foods because they don’t taste them strongly; and tasters, whose likes and dislikes vary. Just as liking sweet food has been shown to be linked to agreeableness, so, in a recent study of 1,000 Americans from a wide range of backgrounds, liking bitter foods was linked to a number of malevolent traits associated with psychopathic personalities. Cheers!

Fatty foods make us happy “For almost everyone,” explains Herz, “fatty foods evoke bliss. We’re programmed to love it.” Just as dopamine, the neurotransmitter governing positive feelings, is switched on by drugs, sex, or some great comedy, it is also the key to the delight we get from food. Just the feel of fat on the tongue, no swallowing required, lights up the reward and emotional centres of the brain. In a study, young adults were assessed for symptoms of mild depression, and split into groups depending on whether they were mildly depressed or not at all depressed. They were then given milk with different fat contents, and all accurately guessed the fat content of each milk sample. After watching some happy and sad film clips, however, the mildly depressed group lost their ability to taste the different fat contents.

Delicious food smells make us eat more Hands up if you’ve wandered into Lidl just to smell the bakery smells. And are they real baking aromas, or buttery-croissantin-a-can? It’s obvious that great kitchen smells make us desire food, but several studies show they also make us overeat. When a group of undergraduates were exposed to pizza-baking smells for 10 minutes before getting the pizza, they ate 43 per cent more pizza than without the smells. In France, diners teased with the scent of a pain au chocolat later chose to eat much higher-calorie desserts than without the patisserie prompt. “Unlike our other senses, smell is directly wired into the emotion, memory, and motivation centres of the brain,” Herz explains. “This is why food aromas are so irresistibly persuasive.”

Why do we eat so much hot sauce? Ever thought of yourself as a masochist? If you’re a liberal user of hot sauce and other spicy foods, you may be what psychologists call a benign masochist. “A bit of unpleasantness in safe circumstances can be thrilling,” explains Herz, likening the experience to watching a horror film or skydiving. Or it may be that eating chilli causes a release of endorphins - “our body’s homemade opioids” - giving us a heroin-like high. By the way, the more chilli you eat, the more you’ll be able to tolerate, as your tastebuds desensitise to the capsaicin burn.

Red means stop Instagram is testament to the appeal of beautiful food, but it’s been proven that the colour red can help us to cut down on snacking - as red is a universal signal for danger, we’re scared of it, unknowingly. In a study of 100 people at a German university, people were served pretzels on red, white, or blue plates. Regardless of hunger or their stated preference for one plate colour over another, those served the pretzels on a red plate ate half as many as the others.

Thinking about food can beat eating it “Imagine that you are really craving Buffalo wings. Now imagine a plate of 20 wings in front of you, all hot and crispy and dripping with buttery hot sauce. Now imagine eating the wings one at a time. Go through the whole sequence in your mind - then imagine doing this another 19 times.” Go on! If you get through this exercise, Herz promises you’ll then eat fewer wings than without the visualisation, because you’ve already stuffed yourself full to bursting with the sensory pleasures of them.

Boredom makes us eat less Lots of us say we’ll eat when we’re bored, but what if it is the food that’s boring? Try eating the same things all the time. This is a straightforward hack for dieters, but can be disastrous in other situations, such as soldiers in action forced to survive on Meals Ready to Eat (MREs). Even refugees in a state of semistarvation reject food if they are offered no variety over a period of time.

Why reusable bags make us buy biscuits Since the plastic bag ban we’ve all got used to carrying reusable shopping bags, and can enjoy that small bump of good feeling when we hit the “own bag” button on the self-checkout.

In the US, however, bringing your own bag is still voluntary in most places, so shoppers aren’t forced into this good deed, and the consequences are surprising: customers are rewarding themselves for reusing a bag, by loading up their trolleys with cakes, chocolate

Why You Eat What You Eat, by Rachel Herz, is published by W.W. Norton & Company Ltd., £20.00