We invest food with so much meaning, and rightly so: it changes our mood, it strengthens our relationships when we eat together and food choices express who we are.
But food has a dark side. We worry about eating unhealthy, about weight gain and how we can control our intake. Eating is not just pleasure; it is also about the struggle with ourselves.
In the last few decades we've learnt an enormous amount about the psychology of food. Here are 20 of my favourite findings.
1. America's terrible relationship with food
Americans have a very dysfunctional relationship with food.
Compared with the French, Belgians and Japanese, Americans get less pleasure from food and are most obsessed with whether it is 'healthy' or not (Rozin et al., 1999).
In contrast, the French have fewer hang-ups and enjoy their food the most. Perhaps it's no coincidence that they are also half as likely to be obese as Americans.
Americans, then, get the worst of all worlds: they are more dissatisfied with what they eat, are more concerned about whether it is healthy, try to make more dietary changes and are twice as likely to be obese as the French.
Something has clearly gone badly wrong with America's relationship with food.
2. You don't know when you're really full
We tend to think that the amount of food we eat is a result of how hungry we are. It's a factor, but not the only one. We are also affected by the size of the plates, serving spoons, packets and so on.
This has been most memorably demonstrated in a study where participants ate out of a soup bowl that was filled up secretly from under the table (Wansink et al., 2005). Others were served more soup in the usual way. Those eating out of the magically refilling bowl had almost twice as much soup but felt no less hungry and no more full.
The moral of this strange tale is that our stomachs provide only crude messages about how much we've eaten. Instead we rely on our vision and the eye is easily fooled.
Here's my healthy eating tip: force yourself to buy smaller packets of everything. Oh, and get rid of your automatically refilling soup-bowls: they're really doing you no good at all.
3. Fat = bad?
This is a great example of the law of unintended consequences.
Many people have come to believe that high-fat food is bad. Public health campaigns, books and articles in the 80s promoted this idea.
Here are the problems. Not all fats are bad; in fact some are very good, necessary parts of our diet. As a result people avoid small snacks with high-fat content in favour of large snacks with low-fat content. In reality the low-fat snack may have way more calories simply because it's much bigger.
Because people think that fat=bad, some foods get unfairly categorised as bad for us, while other low-fat foods are supposed to be good. This leads to the situation were people regularly under-estimate the amount of calories in low-fat, 'good' foods and over-estimate the calories in high-fat 'bad' foods (Carels et al., 2006). The difference in that study worked out to about 35%.
The same is true in restaurants where dishes billed as 'healthy' are estimated by diners to contain up to 35% less calories than they really do.
4. It's never 'just lunch'
Eating together has powerful psychological overtones.
Lunch is a serious undertaking, especially when it's with an ex-partner, according to a study by Kniffin and Wansink (2012). They found that compared with things like having a coffee or talking on the telephone when their partners had lunch with an old flame, it provoked the most jealousy.
The symbolic power of eating with other people is strong: it's never 'just lunch'.
5. Taste fades with age
As we age, our sense of taste gets weaker. One study found that the ability to detect salt was most affected, as was the ability to detect 'umami', now considered one of the basic tastes, along with sweet, sour, salty and bitter (Mojet et al., 2001).
Depending on the exact taste, older people may need between 2 and 9 times as much of a condiment like salt to experience the same taste. Men seem to be particularly affected by this loss in the ability to taste.
The reason is partly that older people have fewer taste buds but mainly that the sense of smell weakens with age. We actually taste much of our food with our noses, so when the nose doesn't work so well, taste sensation is lost as well.
6. Carrots taste weird for breakfast
We tend to think that there's something intrinsic about say, a carrot, that means we either like it or don't. But a simple thought experiment shows this isn't true.
What if you had to eat a carrot, on its own, at six o'clock in the morning? Does it taste the same then as it does mixed in with other vegetables and meat, and eaten at the 'usual' time of day?
The context in which food is eaten affects us much more than we might imagine. This includes the time of day, who is around us and where we are.
7. Fat waitress = fat customer
Here's a case in point for how context affects what you might choose from the menu in a restaurant. McFerran et al. (2010) looked at how the effect of your server's body-weight might affect what you choose.
They found that people who were dieting ate more food when encouraged to choose unhealthy snacks by an obese waitress than when the waitress was thin. You might have predicted exactly the reverse result—surely an obese server will put you off your food. Apparently not. Instead it may unconsciously give people who are dieting 'permission' to overeat. In other words: if she can overeat, so can I!
Incidentally exactly the opposite effect was seen for those who weren't dieting. They ended up eating more when the waitress was thin. This may be simply because attractive (thin) people tend to be more persuasive.
8. Fat friends = fat self
It's probably going too far to say that having fat friends causes us to be fat ourselves, although there is evidence for this. Christakis et al. (2007) found that people's chance of being obese was increased by 57% if they had obese friends.
Still, it's very safe to say that people are enormously influenced by the eating behaviour of those around them. We clearly see in studies that people eat more when those around them eat more, and less when those around them eat less. Women seem particularly susceptible to this.
Even while eating on our own we are indirectly influenced in our choices by society—psychologists call these 'social norms'. When norms are manipulated in experiments, people can be made to eat less or more at will.
One great example is that manly men are thought to eat big meals and feminine women eat small meals. Hence: a steak for the 'gentleman' and a salad for the 'lady'.
9. Eating intentions are beaten by habits
What's the best way to predict what food you're going to eat tomorrow? Should I ask about your intentions, your preferences or that diet you've just started?
Don't bother. All I need to do is ask you what you ate yesterday. The best way to predict what you're going to eat tomorrow is to examine your habits. On average habits tend to trump our best intentions and even our stated preferences.
Changing our eating habits is hard because so many decisions are made automatically, in response to routine situations we find ourselves in, and also because of...
10. Mindless eating
Eating is so routine that we easily zone out from the experience. While our minds are wandering, though, our hands are shovelling it in faster and faster.
Studies have shown that people eat more when they are distracted, like when watching TV or talking with friends (Bolhuis et al., 2013). Unfortunately when not focusing on our food, we tend to eat more and get less enjoyment from it.
This is why one approach that's used to combat eating disorders and obesity is mindful eating. This is taking smaller bites and paying more attention to what you are eating. Not only do people eat less this way, but they also enjoy it more.
11. Suppressing food thoughts leads to bingeing
Regular readers of this blog will probably be bored witless with me going on about how trying to suppress a thought makes it come back stronger. Sorry. Here we go again.
The same is true for food. People on diets who habitually try to suppress their thoughts about food are more likely to experience food cravings as well as being more prone to binge eating (Barnes & Tantleff-Dunn, 2010).
So, don't try to avoid, instead try these 8 alternatives to thought suppression.
12. If it's healthy, you can eat more!
Unfortunately this seems to be a widely held belief, or at least way of behaving. In studies, when people are given the same food, but in one instance it is labelled more healthy, they will eat more than when it is labelled unhealthy. In Provencher et al. (2009), it was 35% more.
It's another situation in which so-called healthy foods can be bad for us because they encourage higher consumption.
13. Anyone for smoked salmon ice-cream?
Food labels and the expectations they set up have all kinds of effects on how we experience food. Most people have now heard about the studies where they put fancy labels on ordinary bottles of wines and magically people say they taste better. It's the same effect if you tell people the wine is really expensive (read more here).
Here's a weirder one, though. Researchers came up with a strange new concoction: smoked salmon ice-cream (Yeomans et al., 2008). But they told some people it was a new type of ice-cream and another group that it was a frozen savoury mousse.
People hated the food when they were told it was a type of ice-cream, but found it acceptable when told it was a mousse.
So it's all very well putting fancy labels on things, but they've got to set up the right expectations.
14. Label it full-fat and it tastes better
Forget about weird ice-cream, what if you take the same food and give it to some people telling them it is 'full-fat' and others that it's 'low-fat'?
Well, they say that the 'full-fat' option tastes better, but they eat less (Wardle & Solomons, 1994). This effect seems to be strongest for people who are most worried about the effect of the food they eat on their health (Westcombe & Wardle, 1997).
15. Bad moods make you eat bad stuff
'Emotional eating' is the idea that the emotions, not just hunger, affect how and what we eat. There is some truth to this.
In experiments, generally when people are put in a bad mood, they are more likely to reach for sugary and high-fat snacks. Negative emotions also make people prefer a snack rather than a proper meal and eat fewer vegetables.
Unfortunately good moods don't necessarily make you eat good stuff. People do seem to eat more when they are in a good mood, but just more of everything rather than specific foods.
16. Healthy foods improve your mood
We know that people who eat more fruit and vegetables are generally more satisfied with life and happier, but we couldn't be sure that it was the fruit and vegetables that were really causing it.
The very latest research, however, suggests that eating fruit and vegetables one day can actually improve your mood the next day (White et al., 2013). This is based on the idea that micronutrients like folates found in fruits and vegetables can help improve depression.
In their 21-day study White et al. (2013) asked participants to log how much fruit and vegetables they ate as well as their mood. This showed that eating more fruit and vegetables one day actually predicted mood the next day. However, they needed to eat 7 or 8 servings for the effect to be clear. So the oft-recommended 5 portions may not be enough to get the full boost to mood.
17. I won't have what she's having
Have you ever been to a restaurant in a group, chosen what you're going to eat, then heard a couple of other people order the same thing and changed your mind?
According to one study this is a recognisable trend (Ariely & Levav, 2000). One of the causes is the desire to be individual and stand out. Ordering something different seems to express individuality.
The punch-line, however, is that in Ariely & Levav's study, people enjoyed their second choices less than their first. Sometimes being different for the sake of it is a kind of conformity (see what I did there to make you feel better about ordering the same thing as other people? Go on, have what you really want!).
18. Small changes beat weird crash diets
If you want to lose weight, forget all those weird diets, whatever they are. The latest fad is the 5:2 diet where you eat normally for five days and fast for two. There's almost no evidence this works. These sorts of extreme diets require big changes to habits, which, as I describe in my book, are hard to make.
Instead of all those crazy diets, it's much better to make small changes that are sustainable in the long-term: by which I mean the rest of your life. Participants in a recent online healthy eating study made very small sustainable changes to their habits and succeeded in losing weight (Kaipainen et al., 2012). Note that they lost weight without going on a diet!
The habits to adopt included: put down your utensils between bites, use smaller plates, drink water with every meal or snack and don't eat directly from the package. It was that simple.
19. The Pepsi challenge
In the same way that lunch is never 'just' lunch, food is never 'just' food. It can also represent an idea and that can influence how we experience the food itself.
Here's an example: Allen et al. (2008) did a version of the Pepsi challenge. Participants were given either Pepsi or a store-brand cola to assess.
Pepsi's advertising encourages the idea that life should be exciting and full of enjoyment whereas store-brand cola doesn't particularly have any marketing message.
The results showed that those who most strongly agreed that life should be full of excitement thought the cola they were told was Pepsi was more tasty. The trick was that often they were just drinking the store-brand cola.
So it's not just the actual taste that affects our evaluations but the beliefs we have about that food or drink.
20. I'm eating an idea and it's a tasty one!
What weird foods have you eaten? Fried bat or tarantulas, an ox penis or tuna eyes?
Perhaps you've been involved in this type of conversation. People start listing all sorts of exotic foods they once tasted—each trying to outdo the last. What's that about? According to one theory we don't just eat food, we eat ideas.
'Conceptual consumption' is our desire to tick boxes on our experiential CVs.
People know, for example, that bacon ice-cream will taste unusual, but there is a clear pay-off in conceptual consumption. It's not just bragging rights, they also like the very idea of each of these things and they want to 'possess' the experience.
It's also about self-image. People want to see themselves, and be seen by others, as interesting people who choose a variety of different experiences for themselves. (Hence the fried-bat-chat.)
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