Wednesday, June 23, 2010

Hunger After Gastric Bypass

I just attended another fabulous conference, The 24th Annual International Conference on Practical Approaches to the Treatment of Obesity. I learned a lot about new surgical techniques and heard an intriguing new way to understand the honeymoon period after gastric bypass. I'll write about that when I have an article to discuss.

Today we turn to the experience of hunger. During the first 12-24 months after gastric bypass, most patients report a drastic change in their experiences of hunger and taste. And they are usually totally surprised and delighted. Someone suddenly prefers yogurt to chocolate. Another can be satisfied with one bite of a piece of cheesecake and literally throw the rest away. Someone else enjoys vegetables for the first time in her life.

Researchers at the Interdisciplinary Obesity Center in Rorschach, Switzerland (I swear, that is not a joke, here's the link: wanted to investigate hedonic hunger before and after gastric bypass and in non-obese controls. By hedonic hunger we mean the drive to eat palatable foods in the absence of energy need. (Think hedonism, the desire for pleasure.)

So, hedonic hunger might include emotional eating, cravings for certain foods even after eating a meal, and that gnawing need for something even when we're not hungry. Before you start cursing human biology for this drive to eat in the absence of the need for calories, let's see if this drive might be adaptive. By adaptive I mean, did it serve an evolutionary purpose? Did a behavior or a physiological response increase an individual's or a species' chance of survival?

I think so. Let's consider a college dorm. I used to use this example with my intro psych students all the time in a discussion of motivation. Let's say you just ate dinner and are comfortably full, about to hit the books for the night. A friend sticks his head in your room and asks if you want in on a pizza. "No, thanks," you say, "I just ate." And you dutifully open your books.

Half an hour later the pizza arrives and the aromas of bubbly cheese, meat and fresh dough permeate the corridor. You are still not hungry but that smell is absolutely unavoidable! Before you know it, you are eating a piece of pizza. And you do feel some hunger and it does taste great. Your appetite changed in response to the environment.

Now replay this vignette about 100,000 years ago when one's appetite needed to adjust itself in response to food in the environment. Let's say you are not especially hungry, but the smell of fresh-killed meat wafts its way to you. It was adaptive for you to generate some hunger and eat because you never knew where your next meal was coming from.

Of course, in 2010, an excess of hedonic hunger can contribute to obesity. Food is so readily available that we do not need to adjust our hunger in response to the environment. But try retraining the primitive parts of your brain to eat only when they are hungry and let me know how that works out!

So, the study. The researchers used an instrument called the Power of Food Scale (PFS) that measures one's mental experience of and preoccupation with food overall and in 3 contexts: when food is available, when food is present, and when food is tasted. Here's a taste (couldn't resist) of some of the items:

      I find myself thinking about food even when I'm not physically hungry.

      When I know a delicious food is available, I can't help myself 
      from thinking about having some.

      When I'm in a situation where delicious foods are present 
      but I have to wait to eat them, it is very difficult for me to wait.

      When I taste a favorite food, I feel intense pleasure.

They had 3 groups of participants: patients preparing for bariatric surgery, patients who had had gastric bypass at least 1 year ago, and non-obese controls. The results are in line with the researchers' hypotheses that hedonic hunger decreases after gastric bypass:

For the total PFS score, the Food Available subscore, and the Food Present subscore, post-bypass patients did not differ from the non-obese controls, and the pre-bypass patients reported significantly higher ratings. Further, the post-bypass patients reported significantly lower on the Food Tasted subscore than both other groups.

So, how does this contribute to our understanding of the gastric bypass honeymoon period? These results show a difference in the post-bypass patients' mental experience of and preoccupation with food, bringing them in line with non-obese controls. The quantitative results of the PFS support the qualitative reports of patients in that first year after surgery.

Two points come to mind, one regarding future research and one regarding an overarching theory. One drawback of this study is that it is cross-sectional. This simply means that the pre-surgery group and the post-surgery group were different people. A more powerful design is a longitudinal approach, in which the same individuals are evaluated before and after surgery. An even more interesting study would be a longer longitudinal approach, to track the mental power of food through the first few years after surgery and gain greater insight into the gastric bypass honeymoon period.

Regarding theory, I can't help but think of one of the diagnostic criteria for substance dependence:

      a great deal of time is spent in activities necessary to obtain
      the substance, use the substance, or recover from its effects.

The mental effort dedicated to planning, obtaining, consuming, and enjoying the effects of an addictive drug can become ritualized, with favorite settings, companions, utensils, and other environmental factors necessary for the full experience of the substance. Might the preoccupation with obtaining food, preparing food, sometimes sneaking food, consuming food and recovering from its effects be considered in the same light? I'm not saying I think all food is addictive (see previous posts) but there does seem to be a similarity in the mental experience of those who struggle with both food and addictive drugs.

Schultes, B., Ernst, B., Wilms, B., Thurnheer, M., & Hallschmid, M. (2010). Hedonic hunger is increased in severely obese patients and is reduced after gastric bypass surgery American Journal of Clinical Nutrition DOI: 10.3945/ajcn.2009.29007

Lowe MR, Butryn ML, Didie ER, Annunziato RA, Thomas JG, Crerand CE, Ochner CN, Coletta MC, Bellace D, Wallaert M, & Halford J (2009). The Power of Food Scale. A new measure of the psychological influence of the food environment. Appetite, 53 (1), 114-8 PMID: 19500623

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