Your Body’s Response to Chewing & Spitting: The Role of Ghrelin and Obestatin

Shelly’s follow-up post on chewing and spitting, an often overlooked symptom in eating disorders. In her first post, Shelly discussed the prevalence of chewing and spitting among eating disorder patients. In this post, Shelly discusses some of the physiological effects of chewing and spitting. Enjoy! – Tetyana

Your body responds to food long before it reaches your stomach. The taste, smell, even the mere sight of food all act to trigger a physiological response, “priming” the gut by stimulating various enzymes required for proper digestion and absorption of nutrients. This is called the “cephalic response”, and it is mediated by a part of the nervous system that’s generally not under conscious control (the autonomic nervous system). Keep in mind, the actual consumption of food is NOT necessary to trigger this reflex.

As you may have already guessed, the act of chewing and spitting (CHSP) out food activates this response, increasing the secretion of stomach acid, digestive enzymes and insulin, as well as changing one’s metabolic rate. Which leads me to wonder–what are the changes that occur in the body during the cephalic response? Are these responses altered in patients with eating disorders who also chew and spit? If so, how? And are there any long-term consequences of CHSP?

These are obviously very broad questions. To narrow it down, in this post I’d like to look specifically at two hormones involved in appetite control: ghrelin and obestatin.

A little background first. Ghrelin and obestatin are both gut-brain hormones that are secreted (mainly) from the stomach and act on the brain. While ghrelin has many neurological functions (such as buffering against stress-induced depression), it was first identified as a hunger-promoting hormone. Ghrelin is secreted during the cephalic phase, and can promote feeding in multiple ways.

First, ghrelin travels through the bloodstream to areas of the brain involved in appetite regulation. There it acts directly on specific receptors designed to trigger hunger and drive food-seeking behaviours. In fact, injecting humans with synthetic ghrelin was enough to produce feelings of intense hunger. Ghrelin can also make food seem more desirable. It does this by activating the reward system, causing dopamine release at the sight, taste, and smell of yummy foods. Hence, it may play a central role in conveying the pleasure and reinforcing aspects of high-calorie “rewarding” foods. Finally, ghrelin can directly act on the GI tract, blunting the stomach’s “fullness” signal and promoting overeating.

There is much less research on the recently discovered obestatin. However, it seems to directly oppose ghrelin’s effect on food intake, acting as a “brake” for the desire to feed (note, this is a MASSIVE oversimplification).

In the current paper (Monteleone et al., 2008), researchers wanted to know if patients with anorexia nervosa (AN) secrete ghrelin and/or obestatin differently than control subjects when allowed to chew, taste, and spit out food.

To test this, they recruited 8 women with AN (both binge-purging and restricting) and 8 age-matched healthy female subjects. Following an overnight fast and a standardized breakfast, researchers served the women a lunch made up of 67% carbohydrates, 13% protein and 20% fat.

To chew and spit in a controlled setting (in this case, called “modified sham feeding”), the women were allowed to see and smell the food for 5 minutes before chewing and spitting each bite into a napkin. Blood samples were taken before and after feeding (or CHSP) for analysis, and the subjects were asked to fill out the Three Factor Eating Questionnaire (TFEQ) to assess their eating behaviour.

Here’s what they found:

MAIN FINDINGS

• Patients with AN had higher levels of ghrelin before and after CHSP compared to controls. Both groups showed a spike in ghrelin secretion within 30 minutes of CHSP, but AN women showed a much higher peak than controls.

• AN women had higher obestatin levels compared to control women, and showed a much sharper DECREASE in blood obestatin levels 30 minutes after CHSP.

• Blood sugar levels didn’t change significantly after chewing and spitting–there was also no difference in blood sugar levels between AN and control women both before and after CHSP.

• Ghrelin levels after CHSP correlated with TFEQ factor 2 in all women, and TFEQ factor 3 in women with AN.

SO, WHAT DOES THIS MEAN?

In healthy women, CHSP can cause an increase in ghrelin and a simultaneous decrease in obestatin. As mentioned above, ghrelin promotes hunger and food seeking, while obestatin may counteract its effect. Together, these hormonal changes may represent the body’s normal response to the presence of palatable food, promoting the initiation of food intake. To support this idea, increased ghrelin levels correlated with TFEQ factor 2, which measures the tendency to lose control over eating.

In AN patients, base levels of both ghrelin and obestatin were increased, and the hormonal responses to CHSP were significantly enhanced. This amplification of ghrelin increase and obestatin decrease might result in an amplified signal of hunger for at least 30 minutes after CHSP. This is supported by the eating behavior data in AN patients that shows a correlation between enhanced ghrelin levels with TFEQ factor 3, which measures hunger.

Hence, it is conceivable that CHSP may increase hunger levels in AN patients, leading to feelings of a lack of control over eating. This may counteract the patients’ rigid control over food intake and promote more CHSP (or binge eating), resulting in a downward spiral. While this is an interesting study, there are some problems with it.

First, subjects may have swallowed food unconsciously–a nurse monitored their chew and spit session, but a more subjective measure would be to look at cholecystokinin levels (released by the small intestine), which increases during feeding but stays stable during chew and spit.

Second, the number of subjects is quite small, hence I am not sure how generalizable it is to the population at large. Finally, note that this study looked at AN patients undergoing CHSP in a controlled setting–they did not ask whether these patients engaged in CSHP outside of the experimental setting. It is conceivable that chronic CHSP may alter the body’s response to food.

Nevertheless, this study shows that AN patients have enhanced ghrelin and obestatin responses after CHSP, and this may be a strong factor in promoting hunger and loss of control over eating, ultimately leading to more CHSP episodes and/or binging behaviours.

References

Monteleone, P., Serritella, C., Martiadis, V., & Maj, M. (2008). Deranged Secretion of Ghrelin and Obestatin in the Cephalic Phase of Vagal Stimulation in Women with Anorexia Nervosa Biological Psychiatry, 64 (11), 1005-1008 DOI: 10.1016/j.biopsych.2008.04.006

Méquinion, M., Langlet, F., Zgheib, S., Dickson, S., Dehouck, B., Chauveau, C., & Viltart, O. (2013). Ghrelin: Central and Peripheral Implications in Anorexia Nervosa Frontiers in Endocrinology, 4 DOI: 10.3389/fendo.2013.00015