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'Healthy' labels, colourful plates and background noise: Rachel Herz on the hidden influences that shape our eating habits

The New Year has barely begun and already your plans to eat more healthfully are skidding off track. You couldn't help but devour the holiday chocolates. You've nibbled your way to the bottom of a bag of chips, without even really enjoying them. And that kale you've been meaning to eat? It's wilting in your vegetable crisper. But don't fret. Your willpower is probably just fine.

There's a whole host of external factors that determine what and how you eat, from what's written on the packaging and the colour of your dinnerware to the noise level of your surrounding environment. That's the focus of Dr. Rachel Herz's new book Why You Eat What You Eat: The Science Behind Our Relationship With Food, which looks at the many influences on the way we consume and experience food.

Herz is a neuroscientist known for her work on the psychology of smell. She teaches at Brown University and Boston College, and has authored the previous books The Scent of Desire and That's Disgusting. Her latest book offers support for the notion that many of the problems we experience with food, from overeating to picky eating, aren't moral failings. We can't simply will ourselves to eat less or expand our palates – our relationship with food is much more complicated than that. Whether we think a food item is decadent or low-calorie can affect how our bodies respond to it; our appetites are often influenced by the people we're with; and how familiar we are with certain foods determines how filling they seem.

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But understanding these factors allows us to manipulate them to our advantage, Herz says.

"This book should make people feel that they have the power. They can take back the meal," she says. "What I'm hoping is that people can see how they can use this information to change their relationship with food."

Herz spoke with The Globe and Mail about hidden factors that shape our meals, including a little-known factor that makes airplane food taste so bland.

'Healthy' labels

How they influence you: It's probably no surprise that when a food item is labelled "healthy," people tend to eat more of it. Might as well have two helpings of ice cream if it's "low-calorie," right? But just thinking something is healthy can actually change your body's response to it – and not necessarily in a desirable way.

The science: Herz describes a Yale University study in which participants were given the same 340-calorie vanilla milkshake, labelled two different ways. For one group, the milkshake was called "Indulgence" and labelled as containing 620 calories. For the other, it was called "Sensi-shake," and labelled as having zero-per-cent fat, no added sugar and 140 calories.

Those who drank the "Indulgence" shake experienced an immediate surge in the hunger-signalling hormone ghrelin after an initial taste. But a half-hour later, their ghrelin levels plummeted three times more than in those who drank the "Sensi-shake," whose ghrelin levels remained flat. That means simply believing they were drinking a high-calorie shake made participants' bodies respond accordingly; they felt less hungry, regardless of the actual calorie content.

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The take-away: "If … you're interested in not having your body pack on every calorie that's in the food, you should approach all food as it being decadent, to the extent that you can," Herz says.

Familiar foods

How they influence you: What makes food filling? Besides attributes such as being high in fat, providing roughage and being served in solid form instead of as a liquid, Herz says there's also a psychological factor at play: The more familiar a food is to you, the more satiating it seems.

The science: Herz points to a study from the University of Bristol in which participants were shown pictures of various common foods, all in 200-calorie portions, and asked how often they ate them. Then they were asked how filling they thought each food was. Participants rated the foods they consumed most frequently as most filling.

The take-away: Familiar foods act as a signifier that you've eaten or that you're satisfied with what you consume, Herz says, which explains why individuals accustomed to eating rice may only feel full when they've had rice, or why those accustomed to eating meat and potatoes don't feel a meal is complete without those staples. She suggests you can use this to your advantage to train yourself to feel satisfied with eating vegetables.

"If after your lunch, you have a couple celery sticks or a couple carrot sticks or whatever, then that sort of becomes a psychological marker for being full and being done eating," she says.

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Colours

How they influence you: Remember Pepsi-Cola's failed colourless Crystal Pepsi? Or Heinz's short-lived green ketchup? Colour has a big impact on how we experience food, and whether we're willing to consume it. But the colour red, in particular, can influence us in multiple ways, Herz says. Since we associate red with the colour of ripe fruit, it can make food taste sweeter, yet since it is also a signal for danger, it can curb mindless snacking.

The science: Herz describes a German study that invited participants to help themselves to pretzels, presented on either a blue, white or red plate, while they were asked to fill in a questionnaire. Those who were served pretzels on the red plate ate half as many pretzels as those who were offered them on blue or white plates.

"Red works to kind of alert you, first of all," which can make you more mindful of what you're eating, Herz explains. "And at the same time, it also makes you potentially question: Should you consume?"

The take-away: If you want to reduce absent-minded nibbling, choose a red plate, Herz suggests. But she says, if your goal is to try to encourage eating, avoid using red dishes and serving vessels.

Sounds

How they influence you: The loud, continuous hum inside an airplane dampens your perception of saltiness and sweetness, which contributes to the lacklustre taste of airplane food, Herz says. Yet the volume doesn't alter your sense of bitterness, so bitterness may be amplified, and it actually intensifies the taste of umami, or savoury brothy flavours, which explains why tomato juice is such a popular inflight beverage choice.

The science: There are three cranial nerves that innervate our perception of taste, Herz explains. One in particular, the chorda tympani, also innervates our perception of hearing. It transmits taste information from the tongue to the brain, and crosses through the ear along the way, she says. "Loudness actually influences the degree to which our taste buds are able to communicate with the brain and it alters our taste in specific ways."

The take-away: Cranking up the volume can make an umami-rich meal more delicious, but you may want to turn it down in time for dessert.

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