Monday, October 17, 2011

Good food, bad food: The psychology of nutrition

Imagine you are alone on a desert island for one year and you can have water and one other food. Pick what food you think would be best for your health (never mind what food you would like).

Alfalfa sprouts
Hot dogs
Milk chocolate

Paul Rozin, a psychology professor at the University of Pennsylvania, asked people this same question and found that 42% of people chose bananas, 27% spinach, 12% corn, 7% alfalfa sprouts, 5% peaches, 4% hot dogs, and 3% milk chocolate. Only seven percent of people chose a food that could actually offer them enough calories and all the nutrients they needed for long term survival. No, not alfalfa sprouts (not nearly enough calories): hot dogs and milk chocolate. These two animal products (the milk in milk chocolate) provide protein and fat, two necessary nutrients that would be deficient in the other foods. Overall, hot dogs would provide all necessary nutrients, sufficient protein, and a more optimal amino acid balance, suggesting they would be best suited to help you survive for a year.

So why is this psychology professor asking people what type of food they’d want to have if they were stranded on a desert island? Rozin found that people’s beliefs about what makes up a healthy diet is heavily influenced by psychology. In this particular paper (Rozin, Ashmore, & Markwith, 1996), he and his colleagues researched whether people’s views about a healthy diet were biased by something termed “dose insensitivity.” Before I describe what that is, let’s try out a few more of the questions that he asked people.

Do you agree with the statement: “Although there are some exceptions, most foods are either good or bad for health”?

Which diet is healthier (both diets have same number of calories):
A diet that is completely salt-free, or a diet in which you have a pinch of salt every day?
A diet that is completely fat-free, or a diet in which you have a pinch of fat every day?

Which food has more calories:
1 ounce of chocolate or 5 ounces of bread
A teaspoon of corn oil or half a teaspoon of pure animal fat

So, do you think foods are generally either good or bad? 40% of people in Rozin’s sample did. This tendency to dichotomize foods into either being good for one’s health of bad for one’s health seems to bring with it particular “good food” and “bad food” schemas. Good foods are thought to be inherently low in calories and complete in nutrients. Bad foods are thought to be low in nutrients, high in calories and probably filled with heart-unhealthy things. The problem with this? This categorical thinking could lead to avoiding foods that are “bad” in large doses but are essential in small amounts. Also, in another study Rozin found that American’s associate chocolate cake with guilt, whereas the French associate it with celebration. Demonizing foods could lead to guilt, obsession with eating (termed orthorexia), and unhealthy eating habits.

Too much salt is better than no salt at all
Does categorizing foods actually lead people to assume even small amounts of certain foods are unhealthy? Rozin’s results say that for some people, yes. Over a quarter of people (26%) believed a salt-free diet was better than a pinch of salt each day, and nearly a third (31%) believed that a fat-free diet was healthier. He calls this “dose insensitivity.” Salt and fat are essential parts of our diet, conferring health benefits in small amounts. Yet, a sizeable minority of people believed that a diet completely free of these was healthier than a diet with trace amounts.

In line with the good food/bad food categorization, Rozin also found that almost half believed an ounce of chocolate had more calories than five ounces of bread (45%) and half a teaspoon of corn oil had more calories than a teaspoon of animal fat (47%). This confounding of caloric density and caloric intake suggest that a large number of people do tend to assume “bad” foods always have more calories than “good” foods, regardless of dose size. If you think that “good” foods inherently have fewer calories, no matter how much you eat… you might just find yourself eating more calories than you realize.

Cake is for celebration
I came across Rozin’s findings last week when I was reading Michael Pollan’s In Defense of Food. I hadn’t expected to find social psychology research in a book on nutrition, but it made me realize that our cognitions and attitudes shape our beliefs about food as much as any “truth” about what is healthy. I definitely grew up with the beliefs that “protein is good” and “fat is bad.”  No way would I pick a hot dog to be the one thing I eat for a year – hot dogs are unhealthy! I know that we tend to categorize things, and with that comes a host of characteristics that we apply generally to anything that falls into that category (think stereotype). I’d just never thought about the fact that I might be stereotyping my food, assuming that if something can be unhealthy, it must always be unhealthy. This type of belief can create a very unhealthy view of food such associating delicious things like chocolate cake with guilt instead of celebration. Along these lines, there is now even a term (not yet recognized in the DSM) for people who have an obsession with healthy eating.

What did you think would be the healthiest food to eat for a year if you had only one type of food? Did you fall prey to “dose insensitivity”? What else do you think psychology can tell us about eating?

The article:
Rozin P, Ashmore M, & Markwith M (1996). Lay American conceptions of nutrition: dose insensitivity, categorical thinking, contagion, and the monotonic mind. Health Psychology, 15 (6), 438-47 PMID: 8973924


  1. Of note, I've been following a paleo/primal type diet for the past couple of years, and all except for food demonization is addressed. Animal proteins are known to be essential for the B12, minerals and protein composition, fats and their polyunsats and sat profiles are known and addressed and are valued for processing fat soluble vitamins and their role in metabolism, and restricting carbohydrates to those of fruit, vegetables and starchy vegetables helps to increase nutrient density while maintaining appetite and hunger regulation.

    But processed foods are largely excluded in this diet(you didn't address this overtly in your post), and so learning about and incorporating the relative benefits of foods is also an integral part of eating in this fashion.

    I doubt that many folks who eat similarly would make errors in answering the questions.

  2. AEK - I'm curious... what one food did you pick to bring with you on the desert island? Did you get it right? I couldn't imagine picking a hot dog because I think of it as being so highly processed.

    I have heard of the paleo diet but didn't know the details about what it entailed. It sounds similar to what Michael Pollan talks about in In Defense of Food and I like that it sounds like there is an emphasis on understanding the relationship between food and well-being, which is important.

    It would be great if there was a bigger emphasis in education to teach us the basic, vital facts how our bodies get energy and the other essential nutrients it needs to survive, and how different foods help fulfill those needs.

    Thanks for reading!

  3. I actually debated between the hot dog (1st choice) and milk. Both have animal proteins and a mix of sat/unsat fats plus carbohydrates. Because I don't eat processed foods, I wasn't sure what the other ingredients are in hot dogs, but figured the B12 content would be higher and thus provide a slightly more complete nutrient composition - plus could serve as bait to catch fish and animals (the hunter in the hunter/gatherer evolutionary congruence emphasis of the dietary sources). On the other hand, chocolate is rich in magnesium and has theobromine, which is desirable, so either way, I would have been satisfied with those options.

  4. There are about a half dozen scientist bloggers who promote and analyze paleo diets (now being rebranded as ancestral health diets). Overall, it is consistent with Pollan's recommendations in that it emphasizes fresh whole foods, grass fed ruminant meat eaten in nose to tail fashion (meaning to include bone-based broths and organ meats along with muscle meat), plenty of fatty fish, eggs and unlimited vegetables and fruit. Some versions eschew dairy and nuts. They eliminate gluten and legumes due to anti-nutrients, as well as industrial seed oils, non-animal trans-fats (the naturally occurring trans-fats found in dairy are actually beneficial) and highly processed food products.

    What I like about it is that once adapted (or re-adapted to pre-industrial age diets), just about every culture's traditional cuisine is included within these food choices. It makes food shopping easy - perimeter of grocery + farmer's markets. But it also mandates that one tune out all food marketing/advertising which includes piped aromas from restaurants as well as print, web and tv/radio ads, and of course, the ubiquitous free samples found everywhere. The other part that is emphasized is that of the sociocultural aspects of cooking one's own food and eating with others: friends/coworkers/family. It's the antithesis of fast food culture.

    Other lifestyle aspects include the emphasis on eating full meals, the absence of snacking, and the use of intermittent fasting. Many people report the reversal of chronic diseases, the loss of weight due to appetite re-regulation, and better sleep, lower stress and better subjective quality of life. From my casual reading around the science-based blogs, there doesn't seem to be much in the way of people reporting that they don't find this enjoyable or that they have difficulty in maintaining this way of eating beyond the initial adaptation to it.

  5. It does seem based on my casual online reading that the people who do the paleo-type diet experience positive change (particularly weight loss and more energy). As a psychologist, I can't help but wonder how much of that is due to the change in eating habits, and how much is attributable to something else (e.g., placebo effect, the good feeling that comes from making and sticking to your goals, cognitive dissonance in the form of having to justify the "entry cost" of the diet). In "In Defense of Food" Pollan talks about the pitfalls of the current nutritional science studies. I'd love to see the results of an experiment on this! What would we find if we did a study where people were provided with one type of diet or another (meals on wheels - science-style, anyone?).

    Thanks for the insightful comments. I'm personally contemplating my food philosophy and love hearing what others think about the topic!


  6. I just really like the picture of the girl with the cake.

  7. I'm really amazed by the stupidity of homo sapiens.

    Personally, I would chose the chocolate milk. I've basically survived on the stuff in the past, when abroad and short on money.

  8. What food would my children bring? When asked, my 6yo and 14yo simultaneously replied "Pizza."

    Well, bread, tomatoes, cheese, meat, pineapples, olives...

    Pizza it is!