Everything in you (your internal bodily processes) and around you (the environment) helps to control your appetite.
Your continuous need for energy drives your appetite because you need the energy in food to survive.
Early humans had to fight to survive and that meant eating as much as they could because they never knew when food would be available again.
Over time, our environment has evolved to the point where tasty, pleasurable food is readily available and most of us can sit to enjoy it.
Our hardwired survival instincts and the convenience of food nowadays means that it's all too easy to overeat.
The science bit
There's a part of your brain called the hypothalamus which is responsible for monitoring energy balance and controlling your eating behaviour.
Hopefully, you'll never have a reason to find it, but if you did it's located on the underside of your brain at the back, just above your spinal column, and is roughly the size of an almond.
One of the main roles of the hypothalamus is to make sure there is a balance between what you eat and the energy you burn every day.
It does this by controlling your appetite and your desire to be active.
There are millions of signals and receptors detecting nutrients and hormones in your body.
If this alert system detects food and drink in your system, it acts by sending a message to control your food intake and satisfy any hungry feelings.
However, if your stomach is empty, it releases a hormone called ghrelin, which triggers that familiar hungry feeling.
Are you still with me? We've got a little more to go and then I'll explain how it affects you dieting.
Right, as you eat and drink, your stomach starts to fill and that hormone ghrelin starts to find that it's not needed, so you begin to feel full.
*This is important ...
The quicker you eat the less likely you are to notice this happen, which is why you overeat - you miss the signals that your body is telling you to stop.
By slowing down your eating, you are more likely to notice feeling fuller as the ghrelin stops being produced, and guess what, it makes it a lot harder to overeat.
There are also a number of other hormones that play their part in controlling your appetite.
But it's also worth remembering that they are not just managed by how much food is available in your body.
Food that contains protein or carbohydrates can help ghrelin levels drop more quickly, which will make you feel fuller for longer.
So when dieting it's worth increasing your protein intake and high-fibre carbohydrates to make sure you keep your ghrelin low and reduce your urge to eat.
The next hormone that we need to focus on is Leptin.
Now, this is a big one.
Leptin is produced by body fat and helps to control your appetite and your calorie burn.
The more body fat you have, the more leptin is produced.
Leptin should lower the appeal of food and increase your physical activity when your body is storing a good amount of energy.
But, too much body fat or too little can seriously screw up how your body responds to this hormone, and leptin resistance is believed to contribute heavily to fat gain and obesity.
So even though you may be producing lots of leptin by carrying too much body fat, your body may become resistant to its effects.
Insulin is another hormone that helps to control your desire to eat.
The body releases insulin depending on your blood glucose (sugar) levels and high levels of insulin help to lower your desire to eat.
As before ... if you have a chronic energy surplus (high levels of body fat) your body can become insensitive to these hormones, meaning that they are less likely to signal your brain to control your appetite.
Body vs head hunger
That empty feeling in your stomach that you get after not eating for several hours is largely controlled by the process I described above.
Messages and signals in your well-managed body control your needs and want to eat.
If it was only this simple, you'd eat depending on what and when your body tells you, stopping when your ghrelin levels drop, and you begin to feel full.
BUT... we also have to take into account our minds (hedonic hunger).
Which for a lot of us overrides all-natural bodily functions and rationality.
Both conscious and unconscious reactions to our health, environment, history and emotions play a huge factor in our eating habits.
So when we think about our appetites, we also have to include the urge to eat for pleasure as well as to survive.
And the desire for pleasure usually trumps everything else.
Western diets have fast become a pleasure eaters paradise.
You have the cleverness of food manufacturers ensuring that their food ticks all of the right pleasure triggers and then add to that the availability and convenience of food nowadays, you have a recipe for a fast-rising obesity pandemic.
I was watching a tv show the other night where they had robots delivering pizzas on a university campus in the USA. Ordered and paid through an app on your phone, and delivered to your table - the ultimate in fast food.
What's in your control?
We now know that your appetite is controlled by several natural functions in your body and your mind.
As long as your body is working as it should it will regulate the natural cycle of hunger and eating.
We understand that too much or too little body fat can mess up these internal processes and play havoc with controlling your hunger.
We all have a hormone called cortisol which is released when we are stressed.
Cortisol makes your brain less open to leptin. So the more stressed you are, the less likely leptin will help to regulate your appetite.
Plus, the more body fat you have the less leptin you produce anyway. How many of us reach for food when we are stressed?
Makes sense now doesn't it!?
So feeling stressed and overweight? Not a good look when it comes to leptin production.
Poor sleep decreases leptin production too, as well as increasing the amount of ghrelin in your system.
Which means that the increase in ghrelin signals that you are hungry and the decrease in leptin heightens the desire to eat too.
It's a cycle.
You feel stressed at work so you overeat.
That stress affects your sleep so you overeat some more.
You overeat and become overweight, which leads to your bodily systems messing up and you continue overeating.
You keep overeating, you keep putting on weight, you feel more and more stressed.
Take a breath
With the way the modern world is designed, a lot of our eating is dictated by habit and cues throughout our day.
How often do we 'just grab lunch' in between meetings or eat the quickest thing available from the fridge, or Friday night is takeaway and wine night?
Now might just be the time to start looking at your stress levels, your sleeping pattern and start to listen a little more closely to what your body is telling you.
To sum up
Our bodies are built to be a finely tuned machine when it comes to controlling our appetite.
It releases hormones to control our hunger feelings and we should eat based on when those hormones tell us to.
Our minds, influenced by many internal and external factors say otherwise (hedonic hunger).
We eat for pleasure and as a reaction to factors in our daily lives, both past and present.
Gradually, this hedonic hunger takes over and our bodies natural mechanisms stop working, which can culminate into weight gain.
Ben Yates is a personal trainer based at Places Gym Hinckley and Hinckley Leisure Centre in Leicestershire.
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