Like all animals, we need to have a small amount of glucose available in our bloodstream all the time. Our brains require a small but constant supply of glucose otherwise they can not function. If glucose levels fall too low, we may become unconscious or even die.
Glucose is the basic building block for energy. It fuels every bodily function that we have to perform, from those we control ourselves, such as walking, working, playing sport etc., to those that our own bodies take care of for us without us consciously being involved, for example breathing, making hormones, circulating our blood, maintaining our very ability to live!
We all need glucose, but we can have too much of this good thing! So let's explore a little about exactly what it is, how we get it, use it and store it. By really understanding some basic facts about glucose, you will discover why you could be eating good food but storing body fat.
Glucose is a simple sugar: simple, that is, in respect of its molecular structure, C6H12O6. What makes it simple is that it contains only three common elements – carbon, hydrogen and oxygen. This very simple kind of sugar is called a monosaccharide .
It is one of two fuels that the cells of the body can burn for energy. The other is fat. We all need glucose, but surprisingly most of it does not come from actually eating it. Instead, most of our glucose needs are met by our digestive systems breaking down larger molecules of complex sugars and starch, known as carbohydrates. The time and digestive effort it takes for our bodies to convert other carbohydrates into glucose depends on the size and complexity of these larger molecules.
It will take very little time to convert another simple sugar into glucose. Let's take fructose as our first example. It is another monosaccharide, and it has exactly the same chemical formula as glucose, ie C6H12O6. The only difference is that some of the elements are bonded together in a slightly different configuration. Because all the elements are present, in exactly the same amounts, and in a very similar structure, it takes very little time for the body to break apart the structure of fructose to reconfigure it as glucose. In fact there are several monosaccharides all sharing the same formula, but with slightly different structures: allose, altrose, fructose, galactose, glucose, gulose, idose, mannose, sorbose, talose, tagatose. So many sugars – so little time to turn them into glucose! Fructose is the sugar found naturally in fruit, and as you can now see, the sugars from fruit can be used very quickly to provide glucose to the body. This is how it is possible to revive a diabetic patient quickly with a small drink of orange juice!
Just for completeness I should mention that there are some monosaccharides that do not share their chemical formula with glucose, but which still contain the basic building blocks of carbon, hydrogen and water.
The next most basic sugars are disaccharides . These contain two simple sugar molecules bonded together. Sucrose is one good example for us to use here – because it is basically just two sugar molecules, one fructose and the other glucose. Maltose is even better – it is simply two glucose molecules linked together. To convert maltose into glucose, all the digestive system has to do break one bond from a molecule of maltose, and hey presto it has two molecules of glucose! So again, we can see that digesting disaccharides can generate glucose very quickly and easily.
More complicated carbohydrates complexes contain longer chains of sugar molecules bound together. Where they have between two and ten individual sugar molecules in their structure they are called ogliosaccharides . The most complex, with even longer chains are the polysaccharides . The digestive system has to work harder, and it takes a little longer to break the chains, and reconfigure the elements to create glucose, but it still achieves this reliably quickly.
Complex sugars like those found in honey, syrups, milk etc., and the starch found in grains, potatoes, rice, beans and other carbohydrate-rich foods all contain chains of glucose that are bonded together with other substances. During digestion, enzymes break these bonds and release the glucose molecules which are then absorbed into your bloodstream.
Blood sugar balance, or control, is the process of making sure we have enough, but not too much, glucose floating around in our bloodstreams at any one time. As we have already said, it is really vital that there is always some glucose there in the blood, to ensure our brains are able to function. Yet, the amount of glucose in our blood is never static. Our cells are constantly using up the glucose and burning it for energy. Replacing glucose that has been used up is essential for our brains. If the systems that regulate our blood sugar are healthy, the amount of glucose they provide is just enough to replace the glucose used! In this way, you could say we “balance” our blood sugar.
Blood sugar levels naturally fluctuate through the day. However, there are two basic states that we need to consider. One is the fast state and the other is the postprandial state.
The fast state occurs when digestion has been completed, for example at night, while we sleep. With a reasonably balanced diet we enter the fast state three hours after eating. In the fasting state our liver contains normal blood sugar levels by releasing small amounts of glucose from the glycogen stores, or by converting protein into new glucose.
Our levels of insulin, which is a hormone released by the pancreas, tell our livers when they need to provide more glucose into the blood stream. When there is no new glucose being provided into the blood stream from digestion, little insulin is released and the low level alerts the liver to action.
We remain in the fast state until we eat some food containing carbohydrates. After eating, any pure glucose that was present in the food will be absorbed into our bloodstream usually within fifteen minutes. Just fifteen minutes? In fact if we eat glucose itself, it gets into our bloodstream and begins to feed our brain cells even before it leaves our quickly: a diabetic person can be revived with a glucose drink!
When we are talking about carbohydrates we usually think of two categories: refined and complex. Refined carbohydrates are those that will be converted into glucose within a few minutes, whereas complex carbohydrates will take a little longer.
Simple or refined carbohydrates, such as white flour or sugar, typically take between a half hour and an hour to provide glucose into our bloodstream. More complex carbohydrates, such as whole grains may take between one and three hours to be fully digested. During this so called postprandial state, the concentration of glucose in our blood will begin to rise as the glucose following digestion comes pouring in. For those of us with a healthy body, as soon as the glucose levels begin to rise, our pancreases are stimulated to deliver a large burst of insulin. Insulin's function is to activate receptors on our cell walls which allow these cells to take the circulating glucose molecules from our bloodstreams and either burn them for fuel or store them for future use.
Assuming for now that we indeed have healthy blood sugar systems, let's now look at how the body uses other nutrients, and how they can affect our blood sugar balance too!
With this information, you can begin to see and understand why managing food intake is so vital to controlling energy, weight and shape.
In very simple terms our bodies need two main things from food: they need energy, and they need a tool kit to develop, grow and repair our bodily tissues, and substances. The key to a great body is to balance these needs – and especially to make sure that the energy our bodies derive from food matches the amount of energy we need to fulfill our daily activities: too little energy spells trouble, too much often spells even more !
The Glycaemic Index (GI) is a measure of just how quickly a food will be converted into glucose, compared with glucose itself. The higher the GI, the faster the conversion process. So glucose itself scores a full 100 on the GI scale, with refined carbohydrates, made up of simple chains of sugars, scoring very highly, complex carbohydrates next, and protein and fats moderately or less. Our bodies can actually convert proteins into glucose, as we have seen, though the digestion process takes longer due to the complexity of protein structures.
Different mechanisms begin to kick in when we create more glucose than we need to meet our energetic needs. At first it is not a huge issue. Through a process called glycolysis, the excess glucose is converted to glycogen which is stored in our livers and muscles. This is exactly what anlete aims to do with so-called “carb-loading”: it's to make sure that as much glycogen as possible is stored, so that it can provide a back-up of energy for that long race! Glycogen is reliably quickly converted back into glucose, and subsequently energy, whenever we find ourselves in the situation of needing more energy than we have readily available. However, our glycogen stores are not endless – they do become full. On average we can store about 360 calories worth of energy in our glycogen stores – which means that if we need to draw up our reserves for energy, we have 360 calories worth of activity before our bodies have to find a new source of nutrients to convert into glucose.
In situations where we digest carbohydrates without an immediate energy need and our glycogen stores are full, yet another digestive process occurs. This time the excess glucose is converted into body fat, which is usually stored in close proximate to the liver – giving rise to the “apple” shape or the “muffin top”.
If we engage in physical activity and exhaust our readily available supplies of glucose, AND we empty our glycogen stores THEN our bodies turn to our fat stores for energy. When we develop a situation where our bodies begin to use fat for fuel our livers begin to transform protein into the glucose our brains need to keep going. If there is sufficient available the body will get this directly from the protein foods that we eat, such as meat or cheese. However, where there is insufficient dietary protein, our bodies will digest our own muscle tissues.
Let's think about this really closely for a moment: when our bodies begin to burn off our body fat for energy, our livers also begin to break down our lean tissues? Yes!
Because our body can “eat” our own muscle tissues in this way, inappropriate diets that are too low in protein result in a dangerous loss of them. This is one of the ways that most branded diet plans are fundamentally flawed and will lead to unhealthy consequences!
So called 'healthy' food products tend to be reduced or low in fat. The diet industry has relied on low fat alternatives for many years, and there is no sign that this is about to change any day now! Yet, a close look at the product labels is revealing … take out fat, and something has to replace it. Usually this is sugar! These foods have a manufactured imbalance of carbohydrates, proteins and fats, which together are called the “macronutrients”. Low-sugar or sugar-free food products, which essentially seek to eliminate the most highly refined carbohydrates, are no solution either! You can be sure that any dietary rule that requires you to eliminate or seriously reduce any of the macronutrients is fundamentally flawed: for health and well-being you absolutely need all three regularly. Losing weight like this rarely involves losing just fat! Your healthy tissues may well begin to suffer too – and if that damage is not addressed then poor health is a genuine risk.
Proteins and fats are primarily needed to provide the components of the tool kit required for bodily development, growth and repair. They are complex molecules which require a lot of digestive effort, and are converted much more slowly than carbohydrates. When consumed together with carbohydrates they also slow down the rate at which the carbohydrates can be digested – because the digestive system has to work on the meal as a whole. This is the basis of Glycaemic Load (GL). We can even out the rate at which our bodies can convert food into available energy by combining carbohydrates with other nutrients to make a meal that is converted to energy at a rate we can use it, depending on our activities at that time of course. The lower the GL of a meal, the more steadily our digestion will function to derive energy from the food, which means our glycogen stores are not always crammed full, and we will be protected from depositing the abdominal fat that gives us that characteristic apple shape Egypt muffin-top.