Food, Physiology, and Psychology
Evolutionary biology largely determines the fact that many humans instinctively desire foods high in fat when grazing and having meals. The thrifty-gene hypothesis provides a very plausible explanation for this: in previous societies, like that of the hunter-gatherers, humans who were able to find and store fat were favored by natural selection (1). In other words, it is possible that by nature, humans look for calorie-dense foods, which also happen to be quite palatable in their fatty and sugary qualities. Our affinity for foods that can pose health risks if not consumed in moderation becomes a great problem in many modern countries where processed food is in overwhelming abundance as the main type of nourishment. It is manifest in troubles like obesity, heart disease, and other health repercussions which are quite common. Other factors also contribute to our collective attraction to fatty foods. An alarming headline claims that bacon and cheesecake affect the brain similarly to heroin and cocaine (2). While it is notably sensational and dramatic, the reason is simple: addiction.
Foods high in fat have the power to modify motivation and reward systems in the brain (3), which in turn leads to addiction and withdrawal (2)(5). One study found that the hypothalamic orexin neuron system that is activated in behaviors involving rewards e.g. use of cocaine and nicotine, is also activated in conditioned expectation and overconsumption of fatty foods (3). Similarly, another study found that binge and continuous overconsumption of fat and sugar lead to an increased number of opioid receptors in the part of the brain that modulates food intake – in other words, eating fatty and sugary foods becomes more and more pleasurable as an organism follows this diet pattern (5). As in the case of drug addiction, the rats in these experiments gradually built tolerances to the food, needing to eat more and more to compensate for the insensitivity of their brains' pleasure centers (2)(3)(5). When the rats were finally switched over to regular diets, levels of corticotropin-releasing-factor in their brains raised, they were more anxious and showed disinterested in normal food, just like rats who experience withdrawal from drugs.
I am particularly interested to see what kinds of long-term effects diets high in fat as well as withdrawal from these diets would have on the reward systems in the brain. What would the trends in rise and fall of certain reward-related neurotransmitters look like over the course of addiction and withdrawal? How would the amount and type of neurotransmitters be permanently affected when the subject was taken off the diet and put on a healthier, more balanced one? One study's results indicate variation in short- and long-term effects; it found that a high-fat, low-carbohydrate diet provides instant mood elevation, while a high-carbohydrate, low-fat diet results in sustained mood elevation, even after the diet is changed (4). It is possible that while the good effects of the high-fat diet did not last, negative effects could have also been sustained for the long run. Studies that investigate these possibilities would be particularly intriguing and complementary.
Short term mood normalization and elevation can also be found in other foods like Brazil nuts (6) and chocolate (7). Brazil nuts contain selenium, which can regulate mood when selenium levels in the brain are low while chocolate can provide mild central nervous system stimulation, alertness, and improvement in mood. The vitamin C in oranges has similar effects: mood improvement and reduction of irritability (8). On the other end of the spectrum of mood, we find a range of mood disorders like depression. Researchers have found that people who followed a processed-food (i.e. high-fat) diet for the duration of their experiment were 58% more likely to develop depression than those who followed a regimen of whole foods (9). A separate study found similar results where Mediterranean diets (rich in vegetables, fruit, fish, and whole grains) put people at a much lower risk for depression than others. Perhaps these issues and the ones that extend out of them in countries like the United States, like the overdiagnosis of depression and ADHD, can be reduced through changes in the way the average person eats. These problems caused by diets heavy in fatty, processed foods are unsettling because of the cause's invisibility: Americans acknowledge frequently that there are health issues to be addressed, but gloss over their source by keeping their diets the same, according to what is commonly found in the culture.
In addition to the modification of reward and mood systems in the brain, fatty foods have the power to create emotional attachment in the people who follow high-fat diets. Findings from a study conducted by Columbia University's Medical Center revealed the emotional impact the foods had on its participants (10). The participants were put on a diet that aimed to cut 10% of their weight. Afterward, the researchers used fMRI scans to see which parts of the participants' brains were activated when they saw photographs of food. Overall, there was an increase in blood flow to the emotional centers of food intake control, rather than to executive function centers. It would be interesting to conduct the same experiment in another country where the focus on food was more of the traditional, whole type rather than of the commercial, processed type, where the average 5-year old does not see about 4000 food ads on television annually. In a country where whole foods were integrated into its cuisine, culture, and national identity, food could still have an emotional impact, but perhaps one that is not associated with intake control but say, the interpersonal relationships with the people with whom food is shared.
Considering all of the above – the evolutionary biology, addiction potential, moods elevation, and emotional attachment – when do we choose to eat things other than the fat-laden foods that are so easily within reach? The most obvious characteristics we might think of are the taste, texture, smell, color, presentation, and feel which inform our choices. Besides these characteristics, would it be possible that the various compounds found in different foods that can alter our psychology (by altering our brains’ physiology) directly impact the way we perceive the foods that contain them? In other words, I wonder if choosing food can be determined completely by a direct physiological impact that bypasses conscious preference and choice. I am interested to see the physiological effects diets that consist of more whole and balanced foods would have on the brain, just as how diets high in fat can affect the physiology of our brains and the choices we make.
In class, we acknowledged that it is impossible to know of and be aware of every process and minute detail regarding our bodies. Eating and choosing foods, something we are so familiar with, seem like they could be analyzed more easily (as opposed to something not involving conscious knowledge and choice, like reflexes and motor control), but is actually far more complicated when we consider physiology, psychology, and the i-function. What is the relationship between all of these elements when we choose to eat certain things and not others? How do each of these elements factor into the choices we make several times a day? It seems so intuitive that we prefer some foods over others simply because we like how they taste, but perhaps we are attracted to these foods for any of the above reasons (which at best, constitute only a small slice of the gamut).
Let's take one of my favorite foods for example, In-N-Out cheeseburgers, which I thought I loved my whole life completely by conscious choice. Without a doubt, the soft, spongy buns, fresh melted cheese, medium-rare patty, crisp lettuce and tomato, all drizzled with a secret sauce please the palate almost universally, across culture, generations, and backgrounds. I have grown up on the stuff and I know I love it, but we now have to consider other factors. Do I love the cheeseburgers because I am a human being who shows vestigial characteristics from eras past? Perhaps it is because I've grown up in America, or because I used to be addicted to fat. It could be any of these reasons, and this is why I am intrigued by this complex relationship. I would be interested in seeing if there was a way to delineate it, something that is so muddled together because its elements are so interdependent. On a personal level, I would like to see why we as individuals enjoy eating certain foods and be able to attribute them to evolution, physiology, psychology, or some other reason. Human choice, overall, is fascinating, considering we can bypass our biology, evolutionary characteristics, and brain’s physiology when we keep our eye on the prize.
The recent research that has found the forces that have powerful influence over the choices we make about food reveal significant patterns in the neurological workings of the human brain. The systems and circuits activated in both subconscious and conscious food choice are also involved in other areas of human life – moods and emotions, addiction and withdrawal, as well as broader concepts like evolution and society. The connection between all of these concepts within the human brain is intriguing, and hopefully future research in the area of food will reveal further connections between concepts previously perceived as unrelated. This research has broader implications than just within the highly specialized fields of academic science, as it is through these chance, serendipitous findings that help further our familiarity with ourselves and the human condition.
1) Diabetes Mellitus paper, on the NIH web site, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1932342/?tool=pmcentrez
2) Junk food addiction article, on the Free Library web site, http://www.thefreelibrary.com/Junk+food+turns+rats+into+addicts:+bacon,+cheesecake,+Ho+Hos+alter...-a0212915724
3) Reward systems article, on the PhysOrg web site, http://www.physorg.com/news167912905.html#
4) Withdrawal article, on the Scientific American web site, http://www.scientificamerican.com/podcast/episode.cfm?id=diet-and-the-brain-09-11-10
5) Brain receptor alteration article, on the PhysOrg web site, http://www.physorg.com/news167936267.html#
6) Food and neurotransmitters article, on the Middle Tennessee web site, http://frank.mtsu.edu/~studskl/food.html
7) Chocolate paper, on the Serendip web site, http://serendip.brynmawr.edu/bb/neuro/neuro04/web1/kcoveleskie.html
8) Mood and food article, on the Eastern Progress web site, http://media.www.easternprogress.com/media/storage/paper419/news/2006/10/05/Features/In.A-Bad.Mood.Check.Your.Food-2332182.shtml
9) Depression and diet news article, on the BBC web site, http://news.bbc.co.uk/2/hi/health/8334353.stm
10) fMRI study article, on the NPR web site, http://www.npr.org/templates/story/story.php?storyId=123894109&ft=1&f=1001