Nutrition
Blood Sugar &
Glycaemic Index
Lesley Loizou
T
he human body is designed to run on carbohydrates (CHO). While we can use protein and fat for energy, the easiest and most ‘smoke-free’ fuel is carbohydrate. Vegetation consists mainly of carbohydrate. We eat the carbohydrate and, in the presence of oxygen from the air, break it down to release the stored solar energy, which provides energy for the body and mind.Carbohydrate is broken down by the body into simple sugars (glucose, fructose, galactose) and stored as glycogen. Glycogen is a large molecule - 1 part glucose and 9 parts water – and, therefore, our ability to store this energy is limited. There are 2 main glycogen stores in the body:
Our Muscles: Contain about 300g of glycogen that is influenced by exercise, carbohydrate intake and training status. At rest, utilisation of muscle glycogen is negligible.
Our Liver: Contains 100g of glycogen that is used to maintain a constant plasma glucose level between meals and during exercise. Liver glycogen supplies other organs, such as the brain and heart, that rely on glucose for their energy needs.
The amount of glycogen stored in your muscles and liver has a direct effect on your exercise performance. High levels allow you to train at optimal intensity and achieve a greater training effect. Low levels will lead to early fatigue, reduced training intensity and sub-optimal performance. In order to get the most out of your training sessions, you need to make sure that glycogen stores are high, thus helping to improve endurance, reduce daily exhaustion, and enable you to exercise longer and harder. However, if you consume too much, then your body will convert the excess to fat!
At rest, we have about 24 hours’ worth of glycogen to keep us going. During exercise lasting >90 minutes, this is greatly diminished. Therefore, intake of carbohydrates is required on a daily basis under normal circumstances and during exercise which lasts >90 minutes. If glycogen levels continue to fall during exercise >90 minutes without being topped up, we ‘hit the wall’ or ‘bonk’. This refers to a feeling of exhaustion reached when the body can no longer provide enough glycogen to maintain the exercise work rate.
What is also important in achieving optimal performance, is to make sure the energy that is obtained from carbohydrates is released in a controlled manner. What do we mean by that? In my previous article, I outlined the difference between complex and simple carbohydrates, and the idea of stabilising blood sugar levels; it is this we must fully understand in order to make sure we have consistently high levels of energy, better concentration and improved performance. If we get any aspect of our intake wrong (quantity, quality or timing), then a blood sugar imbalance occurs, leading to fatigue. If this continues on a regular basis, we can experience many other health problems.
The absorption pyramid shown at the end of the article illustrates the different types of carbohydrates, with those at the very bottom passing through the digestive tract largely unchanged and those at the top being quickly absorbed by the body, causing a rapid rise in blood sugar levels and the need for your body to release insulin to deal with the influx of sugar. The glycaemic index (GI) measures the reaction of the human body to the ingestion of a portion of food that contains carbohydrate; therefore, the GI is used as a guide to determine which foods are slowly absorbed and which foods are quickly absorbed.
Carbohydrates start to be digested in the mouth (by salivary amylase); when they reach the stomach, this digestion stops temporarily with the stomach focusing on the breakdown of protein and, in a small way , fats. The time food spends in the stomach very much depends on the CHO, protein and fat composition of a
meal: the greater the protein and fat content, the longer propulsion into the small intestine takes. When the stomach is emptied into the small intestine, CHO digestion continues (by pancreatic amylase); the speed of absorption is governed by whether this food is a simple or complex carbohydrate. It is worth noting that alcohol, which is a simple CHO, is partially absorbed directly through the stomach.
When you eat a high-GI food you experience a rapid spike in blood sugar level. The amount of sugar in your blood must be kept within a very tight margin, so our body responds by releasing the hormone insulin which does two things:
• It quickly reduces the level of glucose in your bloodstream by diverting it into various body tissues
for immediate short-term use (glycogen in the liver & muscles) or by storing it as fat, and;
• It inhibits the conversion of body fat back into glucose for the body to burn as energy.
The result of eating high GI foods is that the body responds very quickly to remove excess sugar and you are left feeling lethargic and hungry. The surge of glucose followed by the rapid drain leaves us starved of energy – so what do we do? If we grab a quick sugar fix, the vicious cycle will continue. We need to eat primarily complex carbohydrates in a timely fashion. This provides us with a constant source of energy and prevents peaks and troughs; however, just before, during and immediately after exercise >90 mins, you will require a combination of simple, moderate and complex carbohydrates. But this does not mean chocolate. Always choose simple CHO that confer other nutritional benefits, such as high GI fruits and vegetables which contain antioxidant & energy producing vitamins and minerals; this should reduce feelings of lethargy, improve recovery time and stabilise blood sugar levels.
Another factor in causing our energy levels to dip is the timing between meals: if we leave long gaps between meals, blood sugar levels drop, resulting in fatigue, lack of concentration, and - more often than not – irritability. When blood sugar levels drop, adrenaline steps in to start the process of converting glycogen into glucose.
The red line in the diagram below illustrates what happens to your energy levels when blood sugar becomes imbalanced: rapid increase and decrease of blood sugar. The green line illustrates a much more even level of energy, within a narrow range, which is what we are aiming to achieve.
This is what happens when blood sugar becomes imbalanced
As athletes, there are several things you need to consider:
• Quality of the food consumed, eg, complex or simple carbohydrates
• Quantity – too little, and during exercise your glucose levels will become depleted, causing you to run out
of fuel. Too much simple carbohydrate will increase insulin levels and prevent conversion of fat to energy
• Timing absolutely critical to ensure consistent high levels of energy, concentration, and to ensure that
It is not as simple as following the GI Index of food: for example, ice-cream has a low glycaemic index; carrots on the other hand have a high glycaemic index score. Would I recommend you had ice-cream instead of carrots? Noooooo… [Ed – damn…] So other things have to be taken into consideration:
• The nutrient content of the food (vitamins & minerals)
• Whether vegetables and fruits are cooked, raw, ripe or un-ripe
• Grains - refined vs unrefined
• What other things you are eating with them – protein & fat (both these will bring down the overall
GI score when combined)
• And to complicate the issue, wheat vs non-wheat grains
Furthermore, as an athlete there will be times when high and moderate GI foods are recommended,
problems with weight control.
Refined carbohydrates have a similar effect: the process of refining - or even cooking - starts to break down complex carbohydrates into simple carbohydrates; in effect, predigesting them. When you eat simple carbohydrates, you get a rapid increase in blood sugar level and a corresponding surge in energy. The surge, however, is followed by a rapid drop as the body scrambles to balance your blood sugar level.
Fruit contains simple sugars, including fructose and glucose. Fruits containing fructose are slower releasing then those containing glucose only; this is because the body cannot use fructose until it has been metabolised to glucose, hence its effects take longer. In addition, fruits, whilst containing simple sugars, also confer many other beneficial nutrients such as fibre. Fibre buffers the effect of simple sugars, contains
antioxidants which support the immune system, has high water content which helps to hydrate you, and lots of potassium to replace that which is lost in sweat. Grapes and dates contain pure glucose so are rapidly
absorbed; apples contain mainly fructose so are more slowly absorbed; banana’s contain both and tend to be quickly absorbed.
Alcohol is absorbed partly through the stomach, so is a very simple sugar! Hence the expression “that went straight to my head” - it probably did! [Ed – Or, normally, straight out of my mouth again]
Wheat Grains Vs Non-Wheat Grains
The current Western diet includes nearly 30% of wheat grains consumed daily, when the recommended amount is actually about 6%. A reduction in wheat intake is recommended, whether you are experiencing typical symptoms of wheat intolerance (eg, fatigue and lethargy) or not.
The reason I have raised wheat as an issue in this article is that, when you are trying to increase your carbohydrate intake it is very easy to go over the top with wheat (eg, bread, pasta, Weetabix), which may eventually lead to you building an intolerance to it, the symptoms of which can be so insidious that you do not relate the two. A blood sugar imbalance and too much wheat will also combine to cause fatigue.
Summary
So, now we know what blood sugar balance is all about, what causes it, and some of the effects it has on us. To avoid rapid changes in blood sugar levels:
• Eat regularly – little & often. Either 5 small meals per day, or 3 meals with 2 healthy snacks
• If your calorie requirement is such that to eat enough would require too much bulk, then use a meal
replacement drink (eg, Complan, Slimfast or Herbal Life). Use one that has a mix of protein and carbohydrate combined with milk for the fat element required
• You can also use these meal replacement drinks when you know that eating solid food will not be
possible for longer then is sensible. For men, the maximum recommended time between meals is 5 hours, and for women, 3 hours. For athletes, I believe that this is too long for men and would suggest you experiment to find the optimum period for you as an individual
• Eat complex carbohydrates, make sure your complex carbohydrates are unrefined (eg, wholemeal bread,
pasta, brown rice, and use wholemeal flour). These give a slow rise in blood sugar and keep a constant level for about three hours
• Combine a small amount of protein with each meal – plant-based protein is better than animal protein
(due to the higher saturated-fat content in meat). The only exception to this is immediately before and during exercise, when simple and moderate carbohydrates are recommended – they need to be quickly and easily absorbed without having to use too much energy to digest. Select foods such as fruit, sports drinks, or meal-replacement drinks, if solid food cannot be eaten
• Small amounts of protein and fat taken with each meal will slow down the rate of absorption of
carbohydrates and give you a greater sense of satiety (‘fullness’). For example, just eating fruit or consuming fruit juice after a heavy session may still leave you feeling hungry but, adding a handful of nuts and seeds to the snack helps to keep you full
• Avoid refined and processed food. This type of food has been stripped of essential vitamins, minerals,
trace elements and valuable fibre content. Furthermore, most processed foods have a high sugar and high fat content. It takes more vitamins and minerals to process this type of food than they provide, therefore
depleting micro-nutrient supply and adding no benefit whatsoever
• Pure fruit juice can cause a rapid change in blood sugar levels because the fibre that is contained in the
whole fruit does not buffer it properly. Dilute pure juices with water to make them less concentrated
• Do not replace sugar with artificial sweeteners; these are alien chemicals which the body then has to deal with. Furthermore, artificial sweeteners do nothing to reduce sugar cravings
• Reduce foods and drinks that are stimulants – tea, coffee, fizzy drinks, chocolate, etc. All these stimulants
cause a fast rise in blood sugar levels, followed by a quick drop. Substitute with herbal teas, water, or diluted pure fruit juices
© Lesley Loizou
Specialist in Sports Nutrition
(RAW dip) Diaita Nutritional Therapist Tel: 01372 811184
