Of all the carbohydrates the body uses, it is often glucose which is frequently misunderstood. The confusion lies around the role of sugar in human physiology, and the difference between sugar as synonymous with glucose, and processed sugar ubiquitous in processed foods.
The brain is extremely sensitive to sugar (glucose) levels; if too high or too low, function is disrupted, and in extreme cases can lead to a diabetic coma and even death. A healthy individual with fasting blood sugars should have less than one teaspoon of glucose circulating in their blood stream at any given time – when you think of how much sugar/carbohydrate is in various things we consume (can of cola drink = 8tsp, glass of orange juice = 4tsp), it puts into perspective how much work goes into keeping our blood sugars regulated.
The role of hormones
When blood sugar levels rise after a meal, insulin instructs receptors to transport glucose out of the blood stream and into cells. A high-GL meal will stimulate greater insulin production than a low-GL meal, therefore dropping the blood sugar levels more rapidly. At this point, glucose will be converted into glycogen, energy or fat.
Someone with good muscle mass is able to store more glucose as glycogen, thereby reducing fat production. This is one reason why resistance training and a high-protein diet that supports muscle mass is helpful for weight management. It also explains why muscular individuals tend to experience fewer symptoms eating a high-GL diet. When blood sugars drop to a low level, the body releases hormones glucagon and cortisol to prop blood sugars up until the next meal. This is achieved by converting liver glycogen back into glucose.
High glycaemic load vs low glycaemic load
A low-GL (glycaemic load) meal provides a slow, steady release of glucose. Low-GL carbohydrates are bound within fibre, which slows digestion and releases carbohydrates over several hours. When low GL carbohydrates are combined with fats, this helps to slow the release of glucose even further.
In contrast, a high-GL meal releases glucose more quickly, causing blood sugars to spike, then with the help of insulin, drop rapidly. A high-GL diet results in extreme blood sugar highs and lows, whereas a low-GL diet leads to consistent blood sugar levels. Low blood sugars can cause dizziness, reduced concentration, sub-optimal performance and, significantly, a tendency to crave the sugary, carb-rich foods that lead to weight gain. If you are exercising on an empty stomach, your blood sugars will be low: this means that there is little carbohydrate readily available to fuel the muscles. You may tend to be weaker, get muscle shakes, reach exhaustion more quickly and possibly feel faint or unwell.
Glucagon, from the pancreas, is the primary hormone that raises glucose levels. However, it is cortisol, from the adrenal glands, which seems to have a more negative impact on health and well-being. As cortisol is a ‘stress’ hormone, it puts the body into ‘fight or flight’ mode, sometimes increasing anxiety, depression, irritability and a tendency to store ‘survival’ fat around the middle. Cortisol is also a catabolic hormone. This means that it promotes the breakdown of muscle, which is the opposite of what most people want to achieve during a workout.
Many individuals believe that exercising without carbohydrates will cause more fat to be burned for energy. However, because cortisol will also be circulating, this will cause muscle loss and therefore, in the long term, lower the metabolic rate and ultimately slow down fat loss. Fats are metabolised more effectively during exercise if moderate levels of carbohydrates are also present in the body. It is generally better to focus on muscle building, which raises metabolic rate long term, than ‘calories burned’ during an exercise session.
The human body evolved with only a limited amount of ‘simple’ sugars coming from fruit and perhaps occasionally honey. The majority of our carbohydrates previously came from complex carbohydrates – that is, sugars stored in the form of starch (root vegetables, vegetables, nuts). With the agricultural revolution, grains and legumes (beans and lentils) became more available. And it is only in the last few hundred years that we began to process grains to get ‘white’ processed carbohydrate products. The body needs dietary carbohydrate but it does not need processed sugars.
This feature was first printed in the October/November 2011 issue of Fitpro magazine.
The views and opinions expressed in this article are those of the author and not of Fitness Professionals Ltd or Virtual Magazine. Consult a qualified health or fitness professional before making changes to your diet or exercise.