Why we get fat

      1 Comment on Why we get fat

Often, overweight people are advised to eat less and exercise more, but the advice is neither appropriate nor helpful.

Overweight people eat frequently because their brain reward centres are generating signals to find food and eat it. At the same time, the brain also sends messages to conserve energy by not moving about much.

In other words, overweight people are not intrinsically lazy – their body chemistry is making them eat frequently, and avoid exercise. It’s a vicious circle: the larger they get, the stronger the chemical signals become.

To understand how to lose weight and keep it off, it helps to understand how the weight got there in the first place. Basically, there are two components involved: the brain, and hormones.

The reward centre

In the brain, a small area called the nucleus accumbens, responds with feelings of pleasure to certain things. Drugs like alcohol, and nicotine, for example.

It’s often called the reward centre, and is the place where repeated pleasurable habits eventually become addictions.

Medical researchers now know that certain foods can stimulate the reward centre, too. Refined carbohydrates, and in particular sugar (a frequent component of modern processed foods and drinks) stimulate the centre, generating feelings that are pleasurable and satisfying.

And just like any other pleasure-inducing substances, repeated stimulation with refined carbohydrates and sugars eventually becomes an addiction to the sugar-containing foods and drinks.

As time passes, the feeling of pleasure with the same amount of stimulation diminishes, and feelings of withdrawl begin. The withdrawl feelings prompt eating more of the foods that give pleasure, and for a short time the pleasure returns.

Eventually the pleasure is blunted again, and even more food is sought to re-create the pleasure. It’s a vicious cycle:

food -> pleasure -> diminished pleasure -> more food -> pleasure -> diminished pleasure -> more food…

Also at play are hormones, which I’ll briefly describe next.


Hormonal control of when to eat (hunger), when to stop eating (satiety), and what to do with the food we’ve eaten (use for energy, store as glycogen, or store as fat) is quite complicated, but for our weight gain/weight loss explanation, it’s not necessary to go into all the intricacies.

To simply things…

Fat is stored energy, and the body likes to have a certain amount of it to use at times when food is not plentiful. It’s a bit like having a few items of food in the freezer in case we can’t get to the shops for a while.

When the fat stores run low in a normal-weight person, the fat cells release a hormone called leptin. Leptin signals the brain that the fat stores need to be topped up.

The brain also receives signals from a hormone produced by the digestive tract, called ghrelin, which tells the brain the stomach and intestines are empty and able to receive food.

The combination of the two hormone signals encourages the brain to generate feelings of hunger, and we look for something to eat.

As the food is eaten, the stomach expands and the release of ghrelin stops. The brain sees that ghrelin has stopped, knows therefore that food is being eaten, and decreases the feelings of hunger.

The vagus nerve also sends signals to the brain to let it know how much the stomach has expanded.

In effect, it’s a balancing act between the vagus nerve saying the stomach is extended, ghrelin saying it’s time to stop feeling hungry, and leptin checking if the fat stores really are satiated.

Weight gain

In a person who is overweight, the signalling appears to have gone awry. The fat cells still produce leptin to tell the brain they’re full, but the brain has become blind to the satiety signal and thinks the fat stores need topping up.

The vagus nerve and the hormone ghrelin also fail to have their usual effect, and feelings of hunger continue to be generated.

As if this weren’t enough, the brain is also feeling withdrawal symptoms from the continual blunting of the pleasure feelings in its reward centre.

The combined result is an uncontrollable desire to find food and eat it, even though body mass is increasing.

And the food group usually sought to satisfy the desire is carbohydrate, especially refined carbohydrates and sweet drinks.

Actually, it’s difficult to eat a lot of protein, or a lot of fat, but most people can eat a large amount of starchy and refined carbohydrates.


Insulin is the hormone that controls the interactions of leptin, ghrelin, vagus nerve signals, and brain reactions, rather like the conductor of an orchestra.

The hormone also controls what we do with the food we’ve eaten. Fats stimulate insulin hardly at all, protein stimulates it a little, but refined carbohydrates and sugars stimulate insulin production a lot.

As I explained in the post ‘Eating starch raises blood sugar and fat‘, carbohydrates are made from chains of glucose molecules. In the digestive tract the chains are dismantled into their component glucose molecules, which are then absorbed.

Fat storage

Some of the absorbed glucose is used for energy production, and some is converted to glycogen and stored in the liver and muscles.

If there’s still unused glucose in the bloodstream, the liver filters it out and converts it to a fat called triglyceride.

Some of the triglyceride is stored in the liver, and the rest is taken to the adipose tissues around our hips and waist and stored in the fat cells there.

These three important processes (energy production, glycogen storage, fat storage) are controlled by insulin.

Blocked access

While insulin is busy conducting the orchestra involved with energy production, glycogen storage, and fat storage, it has another very important effect.

Insulin turns off the enzymes required to use the fat we already have in our fat stores, for energy production.

Although our bodies can happily use our own fat to make energy – thereby reducing the amount of it around our waist and hips – in the presence of a high level of insulin, access to our stored fat is blocked.

And as we know, we get high insulin levels when we have foods and drinks that raise our blood glucose.

In other words, when we have starchy carbohydrates and sugary drinks, our blood glucose rises, our insulin level rises, and access to our fat stores is blocked. That’s why it’s impossible to lose weight unless we cut the carbs.

Losing weight

The only way to lose weight and keep it off then, is to break the cycle of hormones and brain signals that keep us feeling hungry, that makes the brain ignore signals of satiety, that stops us burning our own fat, and that keeps us in the ‘find-food-and-eat-it’ mode.

As we have seen, the leader of the orchestra is insulin.

If we can reduce the amount of insulin produced, we can begin to regain control of the orchestra again.

And the only way to reduce the amount of insulin produced is to reduce the foods that stimulate insulin release – refined carbohydrates and sugars.

LCHF lifestyle

The LCHF lifestyle is the most successful way to lose weight and keep it off, because it effectively keeps blood sugar and insulin levels low.

In addition, the fat and protein foods are filling, and give us a lasting feeling of satiety.

And feeling nicely full turns off the hunger pangs.

LCHF enables us to take back control of the orchestra that led to us putting on weight in the first place.

Starting the LCHF lifestyle

I’ve written about how to get started with LCHF in the category ‘Starting the LCHF lifestyle‘, so please have a look at the posts and drop me a line in the comment box below if you need help with anything.

1 thought on “Why we get fat

  1. Pingback: How added sugar harms us and what to do about it | Thrive Low Carb

Leave a Reply

Your email address will not be published. Required fields are marked *