Carbohydrates - The Basics

CARBOHYDRATES

Carbs are the primary source of fuel for the body, (unless of course you are following a ketogenic low carb diet) but before they can be absorbed and utilised by the cells in the body they must be broken down into a more manageable form, eg, monosaccharides (one single sugar molecule) such as glucose. The ultimate source of glucose is sugars and starches, natural reserves of which are created by energy from the sun, carbon dioxide and water.

Glucose is a vital component of the human body as it serves the brain and the central nervous system. To maintain a continual consistent supply of glucose the body stores reserves in the muscles and liver as glycogen. If you are eating insufficient carbs these glycogen reserves are mobilised and converted back to glucose. Once this glycogen store has been exhausted the body will start to breakdown its own muscle to synthesise glucose. In other words, protein itself (your skeletal muscle tissue) can be broken down into its constituents to form carbohydrate or blood glucose known as glycogen. This sole fact demonstrates, that although our systems are primed and geared towards eating carbohydrate as our main energy and fuel source, this is not the exclusive form of energy. And it is for this reason that carbohydrates are confused in many texts and books as being essential macro nutrients. They are near essential, but life can indeed go on without them. And they can often be classed as rather satiating and delicious food source.

Traditionally carbohydrates have been classified in terms of chemical structure and it was once thought that the more complex the structure of the carbohydrate, the longer it would take to be digested, therefore, complex starch molecules were thought to digested slowly and steadily whilst simple sugars were thought to digest rapidly. We now know from scientific research with real foods and real people that the concept of simple and complex carbs does not really tell us anything about the way they will actually behave in the human body. Instead, we now use a tool called the Glycaemic Index to tell us which foods will be digested and absorbed rapidly and which will take longer. In response to this rise in sugar into the blood stream, your body then produces insulin from the glands of the pancreas and this response is measured using the insulin index.

Carbohydrates that break down quickly during digestion provide a high burst of glucose to the bloodstream. Carbohydrates that are broken down slowly release a steady stream of glucose into the blood. Slow, steady, digestion of foods prevents wild fluctuations in blood-sugar, thus negating the need for the body to break down muscle tissue to top up glucose supplies. This factor spares your muscle tissue and assists in the anabolic process of muscle cell growth and repair. The Glycaemic Index is a ranking of foods from 0 - 100 that tells us whether a food will affect blood sugar dramatically, moderately or just a little. For the majority of people most of the time, slowly digested carbohydrates are preferable to rapidly digested carbs. However, some athletes can benefit from in taking rapidly digesting and absorbing carbs at the right time, a topic we shall return to later.

Slowly digested carbs release sugar into the blood stream in a slow consistent trickle. Consequently, they fill you up and keep your hunger satisfied for longer. Moreover, by maintaining a steady level of available glucose for fuel they enable you to burn more of your body fat without resorting to breaking down muscle protein for energy.

Carbohydrates are natural appetite suppressants.
When you eat a carbohydrate rich meal your body responds by secreting the hormone insulin form the pancreas. Insulin signals the fed-state and stimulates the storage of fuels such as glucose. The greater the rise in blood-sugar, the more insulin produced. Glucose is stored as Glycogen in the liver and the muscles. This storage facility, however, has a limited capacity, any excess glucose that cannot be stored as glycogen enters the adipose (fat) cells of the body and stimulates the production of triacylglycerides. Consequently, if an individual's blood-sugar constantly fluctuates above the maximum storage capacity the excess glucose that they ingest will be stored as fat. Carbs which are digested quickly raise blood-sugar levels very high very rapidly and are therefore likely to push glucose levels above that that can be stored by the body as glycogen. Such foods are therefore likely to promote the storage of fat. Slowly digested carbs raise blood-sugar levels slowly and steadily, just enough to keep supplies of glycogen topped up without stimulating fat synthesis.

Carbohydrates and Peak Sports Performance
The rate at which glucose enters the bloodstream affects the insulin response as outlined above. The higher the blood-sugar increase, the greater the amount of insulin produced in general. Although this rule of thumb is sometimes negated by recent research within the insulin index. This is although a good general rule of thumb. As glucose is the fuel most preferred by the body, its availability greatly affects the exercising muscle.

The primary fuel for exercise is Adenosine Triphosphate (ATP). The rate of ATP synthesis from carbs is about 1.0 mol/min, from fats the rate is only 0.5 mol/min therefore carbs yield approximately twice as much energy as fats.

When we are talking about eating for peak sports performance, the timing of the meal is crucial:

-Before an event
Carbs which are digested and absorbed slowly are able to provide a constant supply of glucose to the working muscle right into the end of a workout when the glycogen stores are running low. How do you know which carbohydrates are going to be released slowly into your system. Well for this you need to refer to the glycaemic index and the insulin index. Where you should be looking for carbohydrate sources and combinations that produce little insulin and have a low GI rating. Remember the primary fuel source used for the brain to function and for heavy endurance activities is indeed glucose (carbohydrate). When you are talking about higher intensity, lower volume activities like brief 40 minute resistance workouts with weights, your body actually burns mostly intracellular fats. This means when you are performing brief and intense weights workouts, protein is of a more critical concern to your carbohydrate levels before a session, and become greatly more important post your exercise session to release your anabolic hormone insulin in order to shuttle vital amino acids back into muscle tissue to initiate repair and of course growth.

-After an event
Quickly digested carbohydrate foods rapidly top-up the depleted blood-sugar stimulating insulin production, the hormone responsible for storing glucose in the muscle tissue. Any glucose eaten after an event when blood sugar is low and stores are exhausted is therefore sent straight to the muscle where it is used for protein synthesis and is NOT STORED AS FAT. So which carbohydrates should you consume immediately after your training. Well you need to refer to the glycaemic index and the insulin index. Here you want to consume high insulin spiking carbohydrate sources and combinations that have a very high GI rating.

After an event it is important to replenish the supplies of glucose used up during intense training. It is also a good idea to take advantage of this state of low blood-sugar to eat foods rich in glucose as, following intense training, glucose will be stored directly in the muscle tissue as glycogen and promote protein synthesis and hence muscle growth.