Sugar is sweet, but it’s also a major fuel for our body.

Where does sugar go in the body and what does it do?

For those of you still subscribing to calorie balance, the ‘calories in versus calories out’ concept, it really doesn’t matter. For you, all the calories go into one big pot. The truth is much more fascinating but also more complicated. I will try to explain.

Sugar and carbohydrates (carbs) break down rapidly in the mouth, stomach, and small intestine into basic simple sugars. Properly known as monosaccharides.

Potatoes break down into glucose, and table sugar breaks down into fructose and glucose. Today we will focus on glucose, the dominant monosaccharide.

Glucose Storage in the Body

Glucose is readily absorbed into the bloodstream and its key role is to supply fuel. The glucose fuel is stored in three separate fuel tank systems: the bloodstream, the muscles (a small tank for each muscle), and the liver.

Fat Storage in the Body

This post is about glucose storage but I need to introduce you to fat storage as well. Believe it or not, fat is a major component of sugar storage. There are two different fats — the fat we eat, and the fat made in the liver from excess sugar. Today we will just refer to the latter.

How Sugar is Turned into Fat

Excess sugar is turned into fat by the liver. This fat is stored first in and around the liver, and then in fat stores around the body. Typically, under the skin. This is called subcutaneous fat.

So, we have three fuel tanks for the sugar and two tanks for the fat. Subcutaneous fat stores most of the energy.

The muscle tanks hold a total of about 80 teaspoons of sugar equal to 1,600 calories. The fuel tanks around each muscle are special. Once glucose is transported into each muscle tank, it can’t leave. The glucose is not available for any other muscle or any other organ.

From an evolutionary point of view that makes sense. A hunter-gatherer who hasn’t seen prey for days will be running short of energy but will still be able to run down the prey when it appears.

You may come across the term ‘glycogen’. It is a slightly more concentrated form of glucose but it is of no concern to us during this discussion.

How the Sugar Fuel is Converted to Energy

Apart from the muscle fuel tanks, the sugar and fat in the other tanks communicate with each other via the bloodstream. They are controlled by the all-important hormone, insulin. The fuel is converted into energy deep inside individual cells in a miniature powerhouse called a mitochondrion. To give you some idea, there are millions of cells in the liver and each one contains about 2,000 mitochondria.

Our blood circulates through a vast network of vessels. Yet the whole bloodstream normally contains between one to two teaspoons of sugar – about 20 to 40 calories. Just enough to keep the body alive for a few minutes.

I remember being astounded that the blood contains just one teaspoon of sugar. When your doctor measures your blood sugar, they hope it will be between a basal level and an upper level about twice as high. About 5 and 11 in Australian units, but don’t worry about numbers.

The blood sugar level is constantly monitored and adjusted by the liver to keep the level steady. The liver contains about 100grms of sugar (Glycogen). This is enough to keep the blood levels stable, at rest, for about 5 hours.

Once it has a full load of sugar, the liver converts any remaining sugar directly into fat. This critically important process is ignored by most of the nutrition authorities and medical practitioners who continue to blame dietary fat for obesity and blocked arteries.

So, Where Does the Sugar go in the Body?

Let’s see how it works on an average day:

We’ll assume we start the day with both the blood sugar and the glucose stored in the liver reduced to basal levels. We haven’t exercised lately so the muscle tanks are all full.

The first mouthful of carbs, maybe milk in a cup of tea. This triggers the release of insulin to transfer sugar from the blood to cells that will burn or store it. Breakfast, consisting of oats, milk, toast and honey and a glass of orange juice will contain 23 teaspoons of sugar. This will completely fill both the bloodstream and the liver beyond capacity – 100grms of sugar is about 20 teaspoons. By the time we are on the way to work, the liver is already converting excess sugar into fat.

breakfast foods and their sugar content

Because sugar and carbs are addictive, it is highly likely that we will feel pangs of hunger in about two to three hours. This is when the blood sugar has returned to basal levels, thanks to insulin.

It may well be that residual insulin will cause the blood sugar to dip below the basal level and cause even more hunger. By now the liver is full of sugar and fat is starting to build up. The snack we have at 10am at work will be mostly converted to fat.

Did you know

the body burns sugar before it starts burning fat?

We can all tolerate small quantities of fat, in the form of droplets, spread throughout the liver. But some people develop fatty liver disease and signs of early inflammation within weeks. Damon Gameau in his brilliant documentary: ‘That Sugar Film’, was an excellent example. While other people are more resistant, at least when young.

How the Sugar Gets Stored in the Body

Apart from being stored as droplets, fat is packaged in the liver inside what I call ‘fat trucks’ and transported around the body to cells that can use or store fat. The trucks are called LDL, low-density lipoprotein. The cells that regularly use fat, may have been supplied with fat by another fat truck called a chylomicron, which carries fat, fresh from what we eat, direct to the cells within minutes or just an hour or two after we eat it. It is more likely that the fat contained in the LDL will go to the subcutaneous fat stores. Read more about Fat Trucks.

Subcutaneous storage has the potential to be long-term. In the case of the hibernating bear, it will almost certainly be converted back into energy during annual hibernation. In our case, unless we are subject to famine or other forms of starvation, it will quite likely sit on our hips forever!

If we decide we don’t want fat on our hips, we might decide to go to the gym and get rid of it. This is a ‘calorie balance’ concept that doesn’t work in the real world.

Let me explain why.

Why Gyms Don’t Work for Weight Loss

For most of us who enjoy a high carb diet, the muscles are organised to burn sugar before they burn fat and the muscles contain about 80 teaspoons of sugar. Even if you were fit enough to burn off 600 calories on the treadmill that would only amount to about 30 teaspoons of sugar.

It is great to go to the gym. There are all sorts of benefits for the heart, the lungs, and general well-being. But losing weight is not one of them. But you will become hungry. The latte and vanilla slice at the café next door will just hit the mark.

After the last meal of the evening, things are set to change. Apart from a tiny amount of sugar in the bloodstream, the only available sugar – 20 teaspoons in the liver, is being used up at about four teaspoons an hour. The sugar is used by the heart, lungs, liver, kidneys and brain, the vital organs that continue to work at night. They all still need a supply of energy. After 5 hours all the sugar in the liver is gone. Provided you haven’t had a mug of Drinking Chocolate at bedtime, from about 1am until breakfast something very important happens.

As the blood sugar level nears basal, the insulin supply from the pancreas switches off and the body converts to using fat as a primary fuel source. We switch from being a sugar-burning machine to a fat-burning machine. Now the control mechanisms keep the sugar up to the basal level.

Fat burning albeit at low levels proceeds through the night until that first cup of tea the next morning.

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