How Does Your Brain Control Eating?

(Note: that is a Z coming out of this CEO’s mouth….. fast asleep!)

Ever wonder about how your brain navigates eating?

In my clinical practice, we talk about the three levels of the brain that are involved in appetite control:

Homeostatic eating (in English: eating for hunger). This is the the most fundamental, basic driver of eating. Homeostatic control of eating resides in the hypothalamus, a part of our brainstem. There are many hormones that signal the hypothalamus to tell us if we are hungry or full. Ghrelin is the only known hunger hormone, which comes from our stomachs. There is a long list of fullness hormones that come from our guts and fat tissue, including GLP1, GIP, PYY, amylin, leptin, oxyntomodulin and others. The balance of these hormones influences how hungry or full we feel.
Hedonic eating: this is eating for pleasure. As part of evolution, we have been built to enjoy food and feel satisfaction and enjoyment from food, as these pleasurable sensations make us want to seek out food (which would have helped us survive in times of food scarcity). The hedonic centers reside in the mesolimbic areas of our brain. Dopamine is the neurotransmitter primarily involved in the wanting of food, and opioid and cannabinoid receptors are primarily involved in the liking of food.
Executive function: this is where we make the decision to (or not to) eat. Think of your personal CEO sitting at the top of your brain (see above), making all the decisions on what you do. The problem is that your CEO loves to sleep, and sleeps beside a computer that has one word on the screen: AUTOPILOT. So if your CEO is left to sleep, the computer will run smoothly, with input from the homeostatic and hedonic areas of your brain, and will send you to make food choices that are often not the best: high calorie, highly satisfying, desirable foods (often high fat and sugar). The autopilot computer will tend NOT to stop you if you are full, because that hedonic centre will keep pushing for more. That is – UNLESS – you keep your CEO awake. Your CEO can make conscious decisions to override the autopilot, to make better choices, to decide whether or not you are really hungry, and so forth. Keeping your CEO awake is what we call mindful eating – eating with conscious decision and purpose, rather than eating ‘just because’ or by default.

In clinical practice, we help people manage weight with these three levels of the brain in mind. Behavioral therapy and teaching about mindful eating are important to help keep that CEO awake and working for you, and to help find sustainable behavioral changes to help to control eating.

Some medications available to treat obesity act in the homeostatic and hedonic centers, which can also help. For example, liraglutide 3mg (Saxenda) is a GLP1 analog, one of the fullness hormones that acts in the homeostatic centre to decrease appetite and increase sense of fullness. Naltrexone/bupropion (Contrave) works in the homeostatic centre, and also works in the hedonic centres to decrease food cravings (anecdotally, many patients on Saxenda also tell me that they have less cravings).

Bariatric surgery (eg gastric bypass or sleeve gastrectomy) increases the production of many fullness hormones. Sleeve gastrectomy also decreases the hunger hormone ghrelin, thereby impacting the homeostatic signals to decrease appetite.

Kudos to my colleague Dr David Macklin for coming up with the sleepy CEO analogy!

Disclaimer: I was an investigator in the research trials of liraglutide as an obesity treatment. I receive honoraria as a continuing medical education speaker and consultant from the makers of liraglutide (Novo Nordisk) and Contrave (Bausch). I am an investigator in research studies of medications similar to liraglutide for the treatment of obesity and type 2 diabetes.

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