Professionals: Digestion begins in the brain

Professionals: Digestion begins in the brain

Educating your clients about the psychology of eating

A valuable part of your role in helping people change how they eat is educating them about the biology of the human appetite system.

Having evolved over millions of years, the human appetite system is mind-bogglingly complex. But you can extract some simple facts and offer them to clients so they better understand their own mind-body processes around eating.

With that understanding, your clients can feel more in touch with their bodies and enjoy a better relationship with food. And you’re happy that you could help them develop this life-enhancing knowledge.

Three phases of digestion

Here’s an important point which can really help your client reduce their overeating. Digestion is a sequence of three phases.

  1. The cephalic phase occurs before food enters the stomach
  2. The gastric phase is a period in which swallowed food activates activity in the stomach
  3. The intestinal phase occurs in the duodenum as a response to the arriving food and it moderates gastric activity via hormones and nervous reflexes

The first of these – the cephalic phase – is where the appetite system is kicked into action and the desire to eat begins. The word cephalic comes from the Greek word for ‘head’ and reflects the fact that human digestion begins even before so much as a crumb has passed our lips.

This is what we’ll focus on here.

The cephalic phase

The cephalic phase involves getting ready to receive food.

Exposure to the sight, smell or taste of food increases salivation and gastric activity and triggers insulin release.

It’s thought that the purpose of this cascade of enzymes and hormones is to gear up the body and get it ready to optimise the digestion of food.

But it’s not just the presence of food that activates this cascade – memory, mood, emotions and associations all play a part. Cues that have been linked with food in the past can set the whole sequence going.

Even just thinking about food gets the system buzzing!

Digestion starts in the brain

Thinking about food (or seeing or smelling it) stimulates the cerebral cortex, which sends messages to the hypothalamus and amygdala then on via the vagus nerve to the stomach.

Of course the stomach doesn’t know that it’s preparing to eat simply because your client just saw a Cheerios ad on the TV.

All too often in our modern world, cephalic phase responses are triggered when we’re not hungry. Understanding this can help your client reduce their non-hungry eating.


The cephalic phase evolved to support healthy digestion

In preparing the body, the cephalic phase of digestion is one of evolution’s numerous ways of helping us get the most from what we eat. It’s thought that cephalic phase mechanisms help regulate the effects of food, so that the sight and smell of our lunch swings our gut into action in ways that prevent the intake of food creating too much imbalance.


This means that as each mealtime approaches or if you’re getting hungry because you skimped on your last meal, this first phase of digestion is doing its job – preparing to receive the food it is ready for.


The cephalic phase evolved before TV ads, Pringles and Snickers

We live in a world where food, or food advertising, is just about everywhere. Adverts can easily trigger the appetite system, whether you’re hungry or not. That’s why they are so effective. They get the biological system going even in the absence of hunger signals.


The cephalic phase is involved in at least four of the five types of non-hungry eating I describe in my book*. Of these, Opportunistic eating particularly involves this brain-activated desire to eat.


Opportunistic eating

“Opportunistic” eating is the term I coined to describe eating something just because it’s there. It’s not lunch time, you hadn’t planned to eat. But someone had left that cake in the kitchen and before you know it, you’re tucking in. For clients who are prone to this type of eating (often because other people leave food around), understanding what’s going on can help stop this unhelpful habit.


How you can help your client reduce opportunistic eating

  1. Explain to them that the reason they’re driven to eat the food they’ve just seen is that the cephalic phase of their digestive sequence has been triggered.
  2. Help them work out how to minimise chance sightings of food like this by organising their home and workspace to reduce the chance of this happening. Simple changes – putting tempting foods at the back of shelves in opaque containers – can prevent such frequent activation of the appetite system.
  3. If your client’s desire to eat is triggered because other people leave food around, suggest to them that when they notice the urge to eat something they’ve caught sight of, they pause and check in with themselves. Were they thinking about food or feeling hungry before they saw the temptation or is this an example of their eyes and brain setting off an urge to eat?
  4. They may be able to tell whether they really are ready to eat because of the time of day, or where they are on the Appetite Pendulum®. Even if it is time to eat, the food left out on the side may not be what they really fancy right now.
  5. If your client wants to avoid opportunistic eating, moving away from the food and finding an activity that occupies their hands and mind will help. They may only need a few minutes of this distraction to be able to get on with their day without giving in to the temptation.


Want to learn more?

If you want to extend your clinical skills in helping clients change unhelpful patterns of eating, please check out the workshops I run for professionals from all backgrounds. All the courses are online for the time being, and if you’d prefer to learn in your own time, you can sign up and have the recordings sent to you as soon as they are ready.



McCarthy, H. (2019) How to Retrain Your Appetite Collins and Brown, London.

Photo by Fakurian Design on Unsplash

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