The Mysteries of Hunger and Weight Loss Explained

Many of my clients complain in the first week of the 6-week coaching program about being hungry or even too full. Others complain about their inability to put on weight or to lose weight. So I thought I would give a fairly in-depth explanation here so that you understand the mechanics behind it all. It will answer the following questions:

• How does hunger work?
• Why do people who lose weight end up regaining it?
• Why does body weight stay relatively constant despite variations in our eating habits and activity levels from one day to the next?

Ghrelin and Leptin – our hunger regulating hormones

Ghrelin is a hormone primarily produced by your stomach before meals and acts on the brain to make you feel hungry. When you are full, the levels of ghrelin go down. However, the sensation of feeling full doesn’t just depend on how physically full it is.

Adipose tissue is where energy in the body is stored – in other words, body fat. The adipose cells produce leptin, the satiety hormone, to stop you feeling hungry by acting on receptors in the brain. More body fat leads to a higher level of leptin in the blood, which in turn reduces hunger. In the past, food intake was thought of in simple terms of calories in and calories out. We now know it is more complex than that. Research data shows that leptin acts on several brain regions and that its effects go beyond the scope of satiety and energy balance.

The Reward System

A particular molecule, dopamine, is associated with food reward. The molecule acts as a neurotransmitter, which carries information between neurons. This information can be interpreted as reward signals. Scientists believe the brain gives a certain reward value to food. This brain reward system is why a full stomach may not stop you consuming food. You would think that someone who has more body fat and therefore more leptin (the satiety hormone) would stop eating and yet they continue to overeat. So “feeling full” is about hormones and adipose tissue as well as about how full the stomach is.

Why does our body try to maintain a constant weight?

Historically, people couldn’t always rely on a steady supply of food, and the body adapted by storing fat so that nutrients were always available. The body likes to store fat for the lean times ahead and it gives it up only reluctantly. To understand how our weight fluctuates only a little over time, we have to look at energy homeostasis. Homeostasis is when your body tries to come back to the norm. It wants things to be constant.

Your adipose tissue (which contains fat cells) makes leptin and sends those signals to the hypothalamus, which is a region in your brain that controls appetite. If you have a lot of fat, the leptin levels will be high to stop the person eating. When a person is lean with little body fat, the levels are low to make them eat.

But other substances also have an effect on controlling your body weight.

• Blood glucose and insulin levels. These are raised after eating sugar-containing foods.
• A hormone called cholecystokinin, which is secreted by the gut when digested food gets into your intestines.
• Ghrelin (as mentioned before), which is an enzyme made by your stomach and intestines when you haven’t eaten for a while.

High leptin and insulin tell your brain enough food has been eaten, so you feel less hungry and it increases how much energy can be burned and you feel energetic. But high ghrelin makes you feel hungrier and reduces how much energy can be burned. So your brain offsets variations in nutrient availability to maintain a balance or energy homeostasis.

What happens when you try to lose weight?

You can have a rapid loss initially for a few days, maybe weeks because you are burning up the stored sugars in the body, which can be accessed more easily. Then the weight loss slows down because the sugar stores are gone and now the body starts burning the fat stores. And as we saw before, when this happens, the low leptin tells your brain that there isn’t enough fat for energy because of its need to reserve it for times of scarcity and so makes you hungrier so you will eat and simultaneously slows down the rate at which you burn energy. So everything in you is screaming for you to eat more. But meanwhile fewer calories are burned.

Why does a person nearly always re-gain the weight they have lost?

It seems that the body has a weight at which it feels comfortable and wants to constantly get back to that. You brain takes over even though you are dieting furiously and tries to force you back to that point. So in the long term, people who lose weight, gain it back. If you persevere at the new weight for long enough, the theory is that you will create a new constant point. But that takes enormous willpower over a long period of time. This could also be why once you have put on weight and stayed there for long enough that becomes the new constant.

Why does an overweight person often eat more than normal?

It is thought that people who stay at a heavy weight for a while can become leptin-resistant so they don’t get the signal that their body has eaten enough. This then messes up the reward system in the brain that leptin is a part of, and so their brain may feel hungry while their body is full. There is a disconnect between the brain and the body.

What can be done about leptin-resistance?

• Reduce or eliminate high-sugar and high-fat processed foods, which cause leptin resistance.
• Eating less calories will eventually correct the leptin resistance.
• Exercising will eventually reactivate the leptin-brain signal.
• Getting 8 hours of good quality sleep a night helps.

To summarize…

So, to sum that up, our bodies do everything possible to store fat and keep a constant body weight. If there is too much leptin in the body over a period of time as in an obese person, then the leptin no longer does its job of telling the body it is full and the brain doesn’t turn off its reward system, so you overeat and the body becomes sluggish to burn less energy and conserve it. However, this leptin resistance can be overcome by caloric restriction.