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June 16

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How hunger works | Your appetite, diet and the role hormones play

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I'm sure you're aware of the sensations of hunger - the grumbling belly and the twisting and writhing of your intestines. It feels like your body aches, waiting for a feed. Knowing how hunger works is important when it comes to managing diet, especially when we restrict calories to lose fat.

Generally, it's almost impossible to ignore what is often an unpleasant and powerful feeling.

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Then, once you've satisfied these hunger signals with breakfast, an opposite sensation occurs. The feeling of fullness and satiety.

Have you ever wondered though how your body actually knows when it's full, and subsequently, when it needs feeding?

Perhaps unsurprisingly, the feeling full response begins as food passes through your mouth. Going down through your food tube, your oesophagus, it enters your stomach, gradually filling it up. As your stomach fills, it expands slowly like a balloon. In turn, the muscular wall surrounding the organ begins to stretch. Nerves that are woven around your stomach detect this stretching and let your brain know.

More specifically, your vagus nerve relays this information up to your brain stem and hypothalamus gland. These are the main areas of the brain that control your food intake, and generally our appetite.

However, that's only part of the story.

There are other mechanisms in place. For example, if you guzzle a large amount of water, your stomach might fill...but not for very long.

Your brain is smarter than that. It works to process hunger signals from a variety of sources. For example, it also takes information from chemical messengers, like hormones. Our digestive system produces these hormones via endocrine cells.

These endocrine cells detect and respond to specific nutrients in your gut and bloodstream. As you can imagine, levels of these nutrients gradually increase as your body digests each meal.

Via the blood circulation, secreted hormones eventually make their way back to your hypothalamus.

In fact, there are more than 20 hormones produced by your gastrointestinal system which play a role in regulating your appetite.

Let's look at one important digestive system hormone

For example, we have one called cholecystokinin. Our hypothalamus reacts to this hunger hormone by reducing that feeling of pleasure and reward you get when eating.

As a result, the sensation of becoming full or satiated starts to creep in, and you stop eating.

Additionally, cholecystokinin also slows down the time it takes for the food you eat to travel from the stomach to your intestines. Consequently, your stomach remains fuller for a little longer. Your brain has more time to pick up the stretch response signals from the nerve cells. It has more time to register that you're actually filling up.

You've probably heard before that it's a good idea to eat slowly. This is why. When you eat quickly, your body literally doesn't have time to recognise what's happening or detect the nutrients it's getting.

The pancreas can detect nutrients and hormones in the bloodstream too. Certain gastrointestinal hormones prompt your pancreas to release insulin. This insulin, in turn, triggers the fat cells in your body to make leptin, another appetite hormone.

This leptin causes a response in your hypothalamus.

The hypothalamus' role in how hunger works

Essentially, when it comes to whether we feel hungry or not, the hypothalamus has two sets of receptors.

One set, when activated, make and release protein molecules that make us feel hungry. The other set produces different chemical messengers that inhibit our appetite and hunger pangs.

The hypothalamus has two sets of neurons important for our feeling of hunger.

The leptin released from your fat cells worked on both sets of hypothalamus receptors. It reacts with and stimulates those that suppress our appetite. Additionally, it also inhibits or blocks the other set which would otherwise keep making us feel hungry.

At this point, you've reached peak satiety - you feel full and have had enough to eat.

Learn how to stave off hunger for longer by knowing how satiety works

Research conducted at the University of Sydney, Australia showed conclusively that some foods lead to long-lasting fullness more than others. For example, some of the most hunger-relieving foods found were boiled potatoes. Conversely, croissants proved particularly unsatisfying and left subjects feeling hungry again soon after.

From this research, we now have the Satiety Index. Basically, it's a list of foods tested and ranked based on how well they fill you up.

Infographic summarising the Satiety Index of Common foods based on research from University of Sydney, explaining how hunger works

Overview of the Satiety Index

As a general rule, foods high in protein, fibre and water tend to keep us feeling fuller for longer.

Even so, that feeling of satiety and fullness won't last indefinitely.

After a few hours, your digestive system will start sending signals to your brain again.

Your stomach, which by now is probably empty, produces new hormones such as ghrelin. These hormones signal to our old friend the hypothalamus to signal to our body that we are hungry. Before long, the rumbling and growling will commence and so the cycle repeats.

Some tips to help you avoid hunger

So now you know how hunger works, it's time to put that knowledge into practice.

Firstly, let's talk about one major factor that will affect your hunger levels.

Calorie deficit.

If you're after fat loss, you'll have to reduce your food intake so that essentially you burn off more than you take in.

However, if you restrict your intake too severely, you run the risk of falling off the wagon. Losses are generally unsustainable as the instinctual cravings from being overly hungry will take over. You'll seek out the nearest food, and you'll eat it. Lots of it.

This is where the professional knowledge, coaching and expertise of someone like myself come in.

We make sure that your calorie intake is managed at a safe and reasonable level.

However, it's worth noting that when you are dieting, feeling a little hunger is natural and ok. Some people cope better with it than others.

It shouldn't in most cases though, ever feel extreme.

How to control your hunger and make appropriate food choices

Learn how to work with your body and its natural hunger signals. Some simple strategies to help you along the way are:

Swap your shakes and liquid food (juices, protein powders, meal replacements, etc.) to real food. Real food that you can eat and hold literally takes up more volume in your stomach. Those stretch receptors will recognise there's more food coming in.

Consider reducing your alcohol intake if you haven't already cut back. Alcohol contains what we call empty calories. More specifically, 7 calories for every gram of alcohol that your body simply doesn't need. If you cut back on your drinking, you can use those spare calories for more food.

Keep yourself busy and occupied. Eating out of boredom is a thing. If you've nothing to keep your mind busy, it'll wander and think about food. Next thing you know, your body wanders off to the fridge.

Although the effect is only slight, drinking coffee in the morning can suppress your appetite.

Make smart carbohydrate choices. Instead of sugary, refined foods like cakes and some cereals, opt for potatoes, rice and pasta. Remember the satiety index - white potatoes are the most filling.

Avoid temptation. If it's not in the house, it's harder to eat. So don't buy the biscuits, sweets and treats when you shop. Out of sight, out of mind.

Fibre is your friend. Coupled with slowly digesting proteins like eggs or cottage cheese, you'll feel fuller for longer. These foods take longer to pass through your stomach and digestive system. As a result, your gut signals to your brain that it isn't ready for more food yet.

About the author

Paul Stokes

Paul Stokes BSc (Hons) is a Certified Personal Trainer, Accredited Sports Nutritionist, qualified Exercise to Music Instructor, Precision Nutrition coach, Massage Therapist and teaches 8 of the Les Mills Group Exercise programs. He currently works in the Oil & Gas industry as a Wellness Coach, imparting his vast knowledge and experience to improve the quality of life of several hundred offshore workers.

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