“Home sweet home,” you say to yourself as you step into your apartment. You are pretty soaked from the walk home in the rain. Who knew it was going to be sunny in the morning, suddenly snowing at noon, and raining by the afternoon? “Damn Raincouver,” you mumble, as you take off your shoes and jacket and grab a towel to dry yourself off.
You’re glad to be home, because it was just one of those laborious and stressful days in the lab when nothing seemed to work. Maybe the ELISA didn’t work; maybe the bands you were looking for on the gel were MIA; maybe someone accidentally left a male mouse in your cage and it decided life was too short to not get frisky with your precious female transgenic mice.
It’s just one of those days.
And now you’ve got the munchies.
You walk towards the fridge and open it.
”I’m out of beer.”
You stick your head in closer and scan the other parts of the fridge, including the freezer, hoping to find some other beverage or food that will be the remedy to your overall unimpressive day.
A few of things you see:
1) Leftover bacon from this morning’s breakfast
2) Leftover salad from yesterday’s dinner
3) Big slice of apple pie
4) Cake from your birthday party
5) Leftover Chinese food from god-knows-when
6) A tub of vanilla ice cream and a tub of rocky-road ice cream
“Score,” you say as you reach out to grab your food of choice. Because you know after you finish eating it, you will feel that much better – or at the very least, feel that much fuller.
For most people, there are certain types of food that we associate with comfort and happiness growing up – although depending on your ethnicity and cultural background, you might have a slightly different take on what your ideal “comfort food” is. Whether it’s ice cream, macaroni and cheese, or chocolate chip cookies, the term “comfort food”, which was added to the Webster’s Dictionary in 1972, is generally defined as “food that gives a sense of emotional well-being,” or “any food or drink that one turns to for temporary relief, security or reward.” 
Although by definition comfort food can be anything the person chooses, the recipes for the majority of comfort foods consist of at least one of the 3 major ingredients: lots of carbohydrates and sugar, high levels of fat, and plenty of love (this last opinion being the author’s own).  In general, the overall effects of comfort food are believed to be partly psychological, through conditioning or cognitive response (i.e. parents giving ice cream to a kid when he/she is sad throughout childhood so that over a period of time, the child associates negative feelings with a craving for ice-cream), and partly biochemical/neurochemical. [2, 3] While the jury is still out on which is the major contributing factor, recent studies in the science community have provided further evidence that comfort food, particularly those high in carbohydrates and fat content, can in fact influence a person’s mood. [2-5]
As such, this paper will discuss some of the proposed biochemical/neurochemical mechanisms behind fat and carbohydrates that are believed to be responsible for bringing you the comfort in your food. Both fat and carbohydrates will be discussed, with a particular emphasis on the latter as it’s the more widely studied component of comfort food.
Mmm…delicious knowledge on fat and carbs…Let’s dive right in, shall we?
Fat – Even the cavemen loved it. (or) Give me butter, and dunk my hand in ice-cold water.
Many types of comfort food contain both high levels of fat and sugar (Timbits, anyone?), but how can fat or a high-fat meal, in particular, affect a person’s mood?
In a study conducted by Sue Zmarzty and colleagues at the Northern General Hospital Trust / Centre for Human Nutrition in UK, the effects of a high-fat meal on a person’s mood – or more specifically, the influence of a fatty meal on a person’s reception to pain – have been demonstrated. In this particular experiment, 16 volunteers (8 male and 8 female) were treated to pancake meals with varying fat content before being subjected to a Cold Pressor Test (CPT), which is essentially a cold-induced pain tolerance test involving sticking your hand in ice-water. After all, there’s no such thing as a free lunch, right?
What the researchers found was interesting. It appeared that the people who ingested the high-fat, low carbohydrate pancake meals 1.5 hour before the CPT experienced a greater reduction in pain reception compared to those who had the low-fat (high-carbohydrate) meals of the equal calorie content.
The researchers concluded from their study that food, especially when rich in fat, may reduce the amount of pain a person feels. 
Even though the exact mechanism through which fat may directly trigger this comforting effect is still unknown, several have been suggested:
I. Fat and Cholecystokinin (CCK) – That satisfying feeling of a full tummy
CCK, a hormone naturally found in our brain and gut, is thought to mediate many of the behavioural responses to fat, such as satiety and tranquilization. [2, 6, 7] Shortly after a person begins to eat, CCK is released in the gut in response to food (particular if fatty food is being ingested). [6, 7] Researchers have suggested that as the level of CCK in the blood rises, it begins to slow stomach emptying and triggers CCK-induced analgesia through the activation of opioid pathways. [2, 6, 7] Eventually, once the blood CCK level reaches a critical level, the person feels satiated, satisfied, and stops eating. As Dr. John Francis, a psychology professor at the Sheffield Hallam University in UK, explained in an interview with Nature news, the effects of CCK after fat ingestion could be one of the reasons that people find high-fat meals more satisfying.  Supersize me, please.
II. Palatability and Fat – Feels good on your tongue because it’s smooth like butter…(and probably because it IS butter!!!)
In addition to the release of CCK in the gut in response to food, it has been suggested that the palatability of foods plays a major role in their ability to relieve negative mood and anxiety in stressful situations; therefore, it’s not hard to imagine the importance of fat (and sugar) in comfort foods. [3, 4, 8] In essence, several researchers proposed that the oral sensation of high-fat food may indirectly cause the feeling of comfort and pleasure in a person by triggering his or her endogenous opioid peptide system (a.k.a. activating the “pleasure pathway”). [2, 3, 9]
Carbohydrate and Sugar – Fuel up!
Not surprisingly, carbohydrates, which make up the majority of the organic matter on Earth, are also found in a variety of foods.  Ranging from milk (seriously! check out that milk carton in your fridge) to pasta to cookies, carbohydrates can be considered the staple ingredient in most people’s diets.
Before jumping into theories which associate carbohydrates and sugar consumption with mood alterations, it is important to recognize that the basic building blocks of carbohydrates are, in fact, monosaccharide / sugar molecules. The term “sugar”, or “table sugar”, that we commonly use, actually refers to sucrose, a simple carbohydrate / disaccharide composed of two basic sugar molecules (glucose and fructose). Regardless of the source, the fate of most digestible carbohydrates, once ingested, are essentially the same – they are broken down by the digestive system into individual sugar molecules such as glucose, which can then be used for processes such as ATP (a type of energy currency in the body) generation and serve as building blocks for other molecules. 
I. Carbohydrates and Sugar – To energy and beyond?
In addition to being an excellent source of energy (i.e. ATP generation), various studies have demonstrated evidence which suggest that carbohydrates and sugar molecules may have an effect on animals’, as well as peoples’, moods and emotional states. [3, 9, 11, 12]
Using animal models, Dr. Mary F. Dallaman and her colleagues reported their observations in the Proceedings of the National Academy of Sciences in 2003. When rats were subjected to stress (no, they didn’t dip their hands in ice water this time; rather, it was periods of cold environmental “stress”) consumed “comfort foods” (lard and sucrose in this case), a change in their stress-related hormonal system could be detected in their blood. The authors described this change as a reduction in dysphoric effects of the corticotropoin-releasing-hormone (a type of neurotransmitter) driven stress-response, and believe this change can influence the mood of stressed-out rats and may ultimately make them feel better.  Likewise, the association between the ingestion of high-carbohydrate meals and improved mood has also been suggested in human studies. In an experiment conducted by Dr. Lloyd and colleagues, 16 people were given breakfasts of the same calorie value but of varying carbohydrate and fat content. To evaluate the test subject, a series of cognitive performance tasks and mood ratings were conducted before and during the three hours following breakfast. Although the results revealed no clear difference in cognitive performances between the test subjects, researchers noticed a significant mood improvement (i.e. decline in dysphoria) in subjects following the high-carbohydrate/low fat breakfast, relative to those who received different diets. 
Unfortunately, the exact details behind how carbohydrates and sugars could potentially induce mood improvement are still unclear. However, several intriguing biological and neurochemical mechanistic explanations have been proposed, which are currently under heated debate and investigation within the research community.
II. Carbohydrates and Your Brain – The ‘S’’s in Happiness stand for…Serotonin?
One of the predominant theories (and perhaps the most widely discussed one), is that carbohydrates increase the level of serotonin synthesis in the brain. [4, 6] This idea is often refer to as the Wurtman hypothesis, proposed by Richard and Judith Wurtman back in the early 70’s.
Serotonin, a type of neurotransmitter found in the nervous system, is known to be involved in mood modulation. [2, 4, 5] The level of serotonin synthesis in the brain is limited by the availability of tryptophan, a type of essential amino acid (building blocks of proteins) we obtain from our diets. [6, 7] This also means that under normal circumstances, when the brain tryptophan level increases, more serotonin is made. 
So where do carbohydrates come into the picture?
According to the theory proposed by Wurtmans, the quick answer is that a high-carbohydrate meal can alter the level of amino acids in the blood.  When carbohydrate is ingested, it triggers the release of insulin in the body, which signals the glucose uptake by the cells.  As well, insulin promotes the uptake of most of the large neutral amino acids (LNAA; such as valine, leucine, tyrosine..etc), but not tryptophan, into the muscles. [7, 8] This is because tryptophan is normally bound to serum albumin (a type of protein found in blood), and insulin essentially increases the number of albumin which bind to tryptophan and prevent it from being taken up by the muscles.  The end result is an increase in ratio of tryptophan to the total amount of other LNAAs, which ultimately means more tryptophan ends up crossing the blood brain barrier into the brain, and more serotonins are synthesized!!! (This potentially means improved mood!)
Although this theory appears plausible, some researchers have argued that there’s a potential flaw in it – the presence of protein in a high carbohydrate meal. [2, 4, 8] Several researchers believe that if proteins are also ingested during the high-carbohydrate meal, the level of many amino acids (including other LNAAs) will increase, which ends up competing with tryptophan and lowering the tryptophan to LNAA ratio, leading to decreased serotonin synthesis. [4, 7] Furthermore, they argue that as little as ~5% of protein in a high-carbohydrate meal, which is rare in human diets, may be sufficient trigger this counter effect. [4, 6]
As such, it’s hard to say exactly how much this theory contributes to the “feeling good” effects of comfort foods. Currently, both sides of the theory are continually being investigated. Perhaps on rare occasions, with the right carbohydrate-rich/protein-poor combination (the Atkins dieter’s worst nightmare), comfort food can help a person feel better through this potential mechanism.
III. Carbohydrate, Sugar and Cholecystokinin (CCK) – That satisfying feeling of a full tummy…again
(Similar idea as to how fat relates to CCK after a person begins to eat)
IV. Palatability and Sugar / Carbohydrate – Sweet! It feels good on your tongue.
As mentioned earlier in this paper, palatability has been suggested to be an important factor in comfort foods’ ability to alleviate negative moods. It has also been proposed that, similar to ingesting fatty foods which have rich fatty texture, the oral-sensory response to sweet/sugary food may stimulate the release of endorphins in the brain. [2-4, 8] Endorphins, a type of endogenous (i.e. produced in your body) neurochemical compound, are thought to be able to interact with the opiate receptors in the brain and induce a sense well-being, improve mood and alleviate pain. [13, 14] Moreover, the link between sweet, palatable taste in comfort foods and analgesia has been reported in a study conducted by Dr. Maxim Lewkowski and his colleagues. In their rather interesting experiment, 72 young adults held solutions of various tastes in their mouth before and during a cold pain stimulus test; what they found was a significant increase in pain tolerance in the group who received sweet tastes compared with those who were given bitter or water conditions. 
Needless to say, although some researchers believe that the release of endogenous endorphins after ingesting palatable food (those with high fat or sugar/carb content) is more likely the mechanism behind “comfort foods”, this theory is still up for debate and currently under investigation. 
Conclusion – Read and eat at your own discretion
After this brief look at some of the theories that have been proposed to explain the effects of “comfort foods”, it is important to remember that these theories are still being tested. (So don’t change the way you eat and what you eat just yet!)
Nonetheless, there appears to be a growing consensus in the scientific community that comfort foods (i.e. those high in carbohydrates/sugar or fat) can improve a person’s mood. The exact relationship between the comfort food and mood, while remaining unclear, is probably a complex one. Factors like the time of eating, the composition and the amount of foods consumed, along with the age, health status and dietary history of the person may all come into play.  Moreover, it is likely that the interaction between comfort food and mood may be a circular one (i.e. how we feel affects how we eat, and how we eat affects how we feel). [2, 4, 14]
As you finish eating the food you picked out earlier from the fridge, you think to yourself,
”That was some good food. Hmm…I wonder if what I just ate has both psychological and physiological effects on me, and if there are any scientific theories that try to associate comfort food and a person’s mood…Maybe it’s—“ you stop your train of thought.
“Nah…I think too much. It’s just food; there’s probably only so much it CAN do anyway.”
“I think I’m gonna take a nap…”
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