It has to do with something called “sensory specific satiety.”
I’ve just taken the last bite of everything I want and need. It’s salted Oreo ice cream from a local ice cream parlor, which I bought in a pint, and I challenged myself to have just three large spoonfuls. After reading Rachel Herz’s forthcoming book, Why You Eat What You Eat, I felt that I could.
Herz is a neuroscientist who teaches at Brown University and Boston College. Her book is full of factoids: the word “salary” comes from ancient Rome, when the Romans paid soldiers in salt; the famous tongue “taste map” is a myth—the result of a half-century old miscommunication; people consume more food at restaurants they think are healthy; “supertasters”—roughly 20 percent of us—are more disgusted not just by bitter flavors but also by decay, disease, and mutilation than regular tasters.
The most fascinating question she answers is why we’re slaves to our cravings. Though first world access to food has never been better, we seem to just be getting hungrier. I talked to Herz about how, in understanding our cravings, we can finally learn to be satisfied.
In your book, you emphasize that what we crave is, biologically, what we evolved to need: fats, sugars, salt. How do our brains use these foods to function?
The brain heavily relies on sugar because its fuel is glucose, and in fact our brains use about 20 percent of the calories we consume on a daily basis to power its vital purposes. Even having sugar right before doing some kind of complex task, like taking an exam, can help you do better on it. Hits of sugar can actually boost cognitive function.
Outside the brain, we need these foods to survive. Sweetness is typically a signal for carbohydrates, a very readily available source of calories. Salt tends to be in our protein sources, and our bodies need protein, so salt encourages us to eat it. And salt itself helps our nerves and muscles function correctly and regulate fluid balance. If we don’t consume enough salt, we die. We also need fat for many aspects of physiological function. Consuming high fat foods is important even in today’s world, if the fat is coming from good sources. Fat has more calories ounce for ounce and tends to feel more satiating than other macronutrients. For example, full-fat yogurt is more satiating than non-fat because fat quells our hunger. So for curbing our cravings, it’s useful to consume fat.
So we need all of these foods to an extent, but it’s possible—and, in our society, all too easy—to have too much of a good thing. Some of us seem to crave these foods, and often consequently over-indulge in them, more than others. Why?
Some people do crave certain foods more than others. People who have a sweet tooth are genetically endowed to have a higher sweet preference. They also get more delight from eating them and more positive effects from them—like getting into a good mood. Our cravings also come from our past—for example, the more salt you use, the more salt you crave. How much we like depends on our previous experience.
But it’s also the case that everyone can fall prey to losing their willpower, especially when they’re under stress, feeling lonely, feeling alienated, feeling disappointed, feeling bored and many other emotional states. Whether you’re a man, woman, psychologically oriented to default to comfort foods or not, we can all be in a situation where we crave those foods if the circumstances push us in that direction. We can all be victim to these desires.
Why does the first bite of something delicious, like ice cream, always taste better than the last?
That has to do with something called “sensory specific satiety.” When we take the first bite of ice cream, it’s novel. It’s like, “Wow I’m feeling everything, I’m tasting everything, I’m getting the full flavor, the aroma.” But when we continue to consume that particular thing, with all its same sensory features, we quite quickly adapt or habituate to it and it no longer gives us the same bang for our buck. And this is well before we can feel that we’re physically full. So before our stomachs start saying, “Okay, I’ve had enough of this,” mentally we start craving something new. This is why Thanksgiving dinner, which has so much variety, is so much of a problem for us: When we have a lot of variety at our disposal, we eat much more. If all we had for dinner was turkey, we would eat way less overall than when we have the turkey plus all the different options.
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You could actually make this into a dieting strategy. If you ate your favorite food—say, pepperoni pizza—morning, afternoon and night, you would pretty quickly find that how much pizza you eat starts dropping, which means that your calorie consumption would also drop. After awhile it’s just going to get monotonous and boring and unpleasant to eat—“Not another pepperoni pizza, please!” So if that’s all you allowed yourself to eat, you would start losing weight. I’m not saying this is a healthy way to lose weight, but you could think of a healthier version, like having salmon, a baked potato and green beans at every meal. If you have no variety in your diet, you eat less.
One counterintuitive finding you cited in your book is that imagining indulging in your craving can actually “mentally fatigue” it, to make it less acute and more resistible. So visualizing myself stripping a juicy buffalo wing to the bone 20 times could make me eat fewer buffalo wings later.
Yes, and the good thing about these imagination tactics is they don’t actually reduce the taste when you eventually do bite into your pizza or chicken wings or whatever you’re craving—unlike what happens when you physically keep eating the same food, which can turn you off of it. But the rub is that people don’t want to sit there say, “Okay, instead of having a slice of pizza, I’m just going to sit here for the next 15 minutes and imagine eating one.” That’d be great if people would actually do that, but not many of us have this kind of self-discipline—especially on a daily basis.
The other thing about craving is it takes a lot of mental energy to disengage from it. For one, willpower takes brain power, and brain power uses glucose. So trying to do these imagination exercises can quite literally sap you of the fuel you need to work. If I’m in the middle of a complex project and having a craving, I may find that, after doing this imagination exercise, I’m not really able to get back into my project.
You write that “Pharmaceutical companies are working feverishly to develop drugs that will take the joy out of jelly and make kale taste like candy, in an effort to motivate healthier eating habits.” Can you tell me about how some of this research could change how we taste food?
Well, for example, drugs could be developed to block the sweet, salty or feel-of-creaminess receptors in our mouth. Another way would be to tinker with the neurons in the taste cortex of our brain to make our favorite things taste like something else less pleasurable [like make sweet things taste bitter]. And another way is to use pharmacological methods similar to what is used to get people addicted to drugs to not want their drug of choice: turn off the pleasure in our brain when we experience these pleasurable tastes.
But a drug like that is not just going to block the pleasurable food. It’s going to block pleasure from lots of other things, too. So there’s problems with doing that. It’s the chore of pharmaceutical companies to figure out if any of this is possible in humans, without it interfering with other things. It’s one thing to do these experiments with rodents and see physiological effects and quite another for these methods to actually work for humans in a way that gives the desired effect without interfering with anything else.
What do you want readers to take away from your book?
I feel like the message of the book is to experience real pleasure from eating by increasing our awareness about what we’re eating and why. A lot of that is just being aware of your body, of your mind, of your surroundings. And asking questions like, “Did something manipulate me that I wasn’t really completely aware of?” Like, “Am I eating these organic cookies because I think they’re not going to be fattening because the packaging says ‘organic’?” Or, as I’m sticking yet another potato chip in my mouth, “Is this actually pleasurable, or not?” Or “Am I eating fast because the music in the restaurant is loud and fast?” “Am I eating more than I would otherwise because I’m socializing with a bunch of friends?” The bottom line is to pay attention while you’re eating so you can understand when your body and your mind say, “yes, this is wonderful” and when they say “no, not so much,” and what that means.
I love food and I want people to enjoy food as much as they possibly can, no matter where they are in their state of wrestling with food. And part of that is realizing that you can get pleasure from just a couple spoonfuls of ice cream instead of half a tub. If you can pay attention, if you’re focusing on just the caramel, chocolate, crunchy almond and creaminess, you’re going to get more out of it in that moment, and that will help you reign yourself in. And then you can say, “That was really, really pleasurable, and I don’t need more.”
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