How the Body’s Hunger/ Fullness System Works

Our bodies evolved to eat small-ish meals

Our problems with weight and eating stem from the mismatch between the systems our bodies evolved for finding, eating and digesting food in periods of variable food availability and the food environment of the 21st Century.

We have evolved a digestive system which allows us to eat food at a meal which gives enough energy to get on with living for a few hours. Once that meal is used up, signals from our gut and other organs tell our brain that it is time to eat again. These signals are experienced by us as hunger. If we eat then, the hunger signals are switched off.

If we don’t eat as soon as we feel hungry, what happens?

If we don’t eat at this point, two things happen. The first is that the body switches over to using up its store of energy (fat) and as a little bit of fat is burned to produce energy, the body registers this as having received more energy and so the hunger signals are switched off. So, if you don’t eat as soon as you feel hungry, the hunger signals will soon pass. This means that tolerating hunger doesn’t mean constant effort.

The second thing to happen is that hunger signals return after perhaps half an hour and gradually get more frequent and stronger, though again if we ignore them they will again subside for a period of time.

This system is governed by a network of nerve connections. As food is being eaten and digested, nerves in the gut and other organs send messages to the brain to register fullness. As food is being used up, the various organs communicate this information to produce the sensation of hunger. The nervous system in the gut itself is so complex that Dr Michael Gershon called it the “Second Brain”.

You can use gentle hunger to lose weight permanently

If you are overweight you may have been ignoring these hunger and fullness signals, possibly for many years. You can learn to tune in to this system for a reliable internal guide to what and when to eat. This liberates you from dieting and you can throw away your diet sheets, meal plans and calorie counters!

The other important point about the biology of the hunger/ fullness system is that it has very close links with two other systems: the Pleasure System and the Anxiety System.

Links between eating and pleasure systems in the body

The Pleasure System evolved to produce the desire to seek out foods which are high in energy, so we naturally enjoy sweet and fatty foods. When we get hungry, the system in the body which tells us what our body needs to eat is activated. If we eat the food our body needs, we experience pleasure and the desire for that food is satisfied, probably after a few mouthfuls of that food. “Sensory specific satiety” means that although we may have had enough of this taste, we may still have a desire for another type of food. After a few mouthfuls of that second food, sensory-specific satiety will again register and the desire for this second food will reduce.

Links between eating and anxiety systems in the body

The Anxiety System evolved to warn us of danger in the environment. For our ancestors, lack of food signalled danger of starvation. Although we now live in conditions of over-supply of food, our basic biology remains driven by anxiety reduction. Feeling hungry can make us feel anxious even though we have plenty of food available. Those of us who become unduly anxious about feeling hungry need to learn that mild hunger is not to be feared and indeed, is to be embraced as a valuable tool in losing weight.

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