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Blood Sugar Control

Blood Sugar Control

In the first of a series of articles nutritionist Matt Lovell will be taking you through the process of becoming diet and supplement aware. This first article explores the relationship between carbohydrate and insulin. It’s fairly detailed reading but the messages are really important to athletes, so concentrate!


Never before have there been as many low fat or fat free products available and yet Western society is more obese than ever. Much of this has to do with people not understanding the link between carbohydrate and insulin, and how these two things relate to body composition. Frequently very fit and talented athletes struggle with poor body composition due to misinformation about carbohydrate consumption.

History of sporting activity and the obsession with carbs.

The aim of the competitive athlete is to win. There is an ever-increasing amount of research being produced that if correctly applied may improve your chances of winning. Looks like good news. Consequently, athletes seem to have to spend an ever-increasing amount of their time sieving through this information in an attempt to identify a gem that may give them the edge. Alternatively, they take advice from more accessible sources like the media articles. Here nutritional generalisations seem to have passed on like folklore. It is perhaps not surprising then that there is a problem. The research that is conducted is usually very specific. Specific to the sport or activity being studied. All too often these specific results have become generalised to “all athletes” and for “all sports” and herein lies the problem.

Much of the early sports research focussed on the nutritional requirements for endurance events. What has been clearly established is that when competing in endurance events, especially those lasting for more than 90 minutes, carbohydrates limit performance. Endurance athletes who are effectively able to carbohydrate load before an event, consume carbs during the event and adequately replenish the body’s stores (muscle and liver glycogen) after an event, will maximise their performance. The timing, type and quantity of the carbohydrate are also all important factors.

This has led to an ‘obsession’ with carbohydrates which has spilled over into other sports almost without exception. This misapplication of knowledge can lead to a reduction in performance. The performance of many power-based sporting activities may suffer, as both protein and essential fat intake have been seen to assume less importance in the athlete’s diet. Many athletes added insult to injury by adopting the general changes that are seen to be occurring in the rest of society where an increasing proportion of calories are being consumed from refined carbohydrates especially due to low-fat foods that contain many hidden sugars. More on this later in the article.

A diet that is high in sugar and refined carbohydrates will lead to an increase in body fat. After eating, the gut breaks down carbohydrates into glucose, the glucose is absorbed from the gut and it is burnt for energy or stored. If the carbs you eat require little digestion, glucose becomes rapidly available in the gut and is absorbed quickly.

Carbohydrates are measured in their ability to raise blood glucose levels through a variety of methods;

• Glycemic Index
• Glycemic load
• Insulin Index
• Satiety Index

For a full list of foods by GI and GL go to

Individual tolerance for carbohydrates varies, something often termed insulin sensitivity. Have a read through the questions and answers below to get an indication whether you are someone who struggles with processing higher levels of carbohydrates. If you think you might be and want to take things further, your GP can arrange for you to do an insulin sensitivity test or glucose tolerance and insulin profile blood test.

Even if you are someone who does not suffer from the symptoms listed you may do well to become carbohydrate aware and ‘clean up’ on refined carbohydrates.

What happens when you eat carbohydrates? The insulin response.

The level of glucose in the blood is controlled by insulin. Insulin acts to ensure that blood glucose levels do not rise above the normal range. It moves glucose from the blood into cells. The faster blood glucose rises the more insulin is produced.

What are the consequences of too much or the wrong type of carbohydrate?

The simple consequence of excess or inappropriate calorie intake from any source, carbohydrate, protein or fat will be their conversion into body fat. Most athletes are acutely aware that “fats” are best avoided and typically aim for a “low-fat” diet. Whilst reducing their saturated fat intake is a good thing, athletes not uncommonly reduce their essential fat intake and inadvertently further increase their intake of refined carbohydrates. This is because when food manufacturers remove the fat from food, to ensure they remain palatable, they add additional sugars and salt to replace the lost taste.

Reduction in essential fat intake, in particular omega 3 intake can lead to insulin resistance over time.

What Goes Wrong?

Poor blood glucose control occurs for a number of reasons. The most common and most important reasons are consumption of rapidly absorbed sugars, over stimulation of the pancreas and nutrient deficiencies, which reduce the impact of insulin in the body.

Insulin, the hormone that can both help and hinder an athlete

Blood glucose levels rise after eating and insulin is released from the pancreas to control this with the aim of maintaining stable blood glucose within the normal range. Outside this normal range our bodies, and particularly our brains, do not function very well. We become confused, disorientated even unconscious. Insulin is the only hormone for storage and a failure of the body to produce it in adequate amounts leads to diabetes.

The more rapid the rise in blood sugar the more insulin is required to control this rise. Insulin, as the hormone of storage, takes glucose from the blood and stores it away. The help that this offers athletes is that insulin will assist the replacement of used muscle or liver glycogen consumed during training or competing, but once the body’s glucose stores are replenished any excess would be converted and stored as fat.

Carbohydrates that have a high glycemic index and glycemic load and that produce a very large insulin response will, particularly when consumed away from exercise, be more readily converted to fat. The reduction of fat consumption and the movement from an intake of complex to refined carbohydrate sources seen in western societies has been paralleled by the increase in obesity in these populations. Athletes are no exception to the human race! From a performance perspective if sugar is converted to fat, body composition will be adversely affected. Similarly if inadequate storage is achieved in muscle and liver cells (as glycogen) the energy stores available for the next exercise session will be reduced and so will your performance.

What we are increasingly seeing clinically are power-based athletes who have adopted the dietary requirements of endurance athletes. As a consequence they typically consume 70% or more of their entire calorie intake from carbohydrate and increasingly from highly refined sources. Whilst their endurance counterparts struggle to keep up their carbohydrate intake to match their calorific requirements the power-based athletes are presenting with a host of symptoms including an inability to reduce high body fats, failure to gain additional lean body mass despite dedicated training, poor concentration and susceptibility to infection.


• Match your energy input (food you eat) with energy output (energy you burn), this is achieved by portion control and increasing physical activity and exercise. Reducing food intake instead will lead to muscle loss instead of fat loss.
• Choose foods that will break down slowly so the body can burn it rather than have to store calories as fat. Foods that are absorbed slowly also have the added advantage of making you feel full and decreasing appetite.
• Eat carbohydrates in expectation of activity. Do not eat large volumes of carbohydrates before bed when requirements are low.
• Eat fast release carbohydrates only following exercise to replenish lost energy

The Glycemic Index (GI) and glycemic load (GL) are the keys to this way of eating. The GI is a number that is given to carbohydrate foods to show how fast blood glucose will rise when they are eaten. To keep things simple, sugar we put in our tea (sucrose) has the top GI value of 100. All other foods are rated against this, and lower numbers are foods that tend to be better for you. GI is only relevant to carbohydrates. The higher the GI the more disruption to blood glucose is caused. The lower the GI the slower the food is broken down. We can therefore use the GI and GL as a guide to which carbohydrate foods one should eat, and when they should be eaten.

To better understand the relationship between blood glucose and insulin, glycemic load is probably more realistic than glycemic index. For instance, an average consumed portion of carrots has very little glycemic load (and is very good for you) this type of carb might have been avoided if the GI had been taken at face value (92). To achieve a GI of 92 almost a kilo of carrots needed to be consumed!

In summary GI is the effect 50g of that carbohydrate has on blood glucose levels and GL is the effect a standard portion of that food might have on blood glucose levels.

There are five factors that effect blood glucose levels after a meal;

• The GI and GL of the carbohydrate
• The volume of the carbohydrate
• The presence of protein in the meal, which slows down the rate at which carbohydrate is digested.
• The fibre content of the food (slows down absorption of the glucose)
• The fat content of the meal (fat slows the absorption of the glucose)

The effect of a meal on blood glucose will be less when the meal includes protein, unrefined carbohydrate, essential fats and fibre. This is a ‘mixed’ or balanced meal. For this reason we recommend that protein should be included in all meals and snacks. We also advise that meals that are high in carbohydrate should be eaten earlier in the day when activity is greatest and energy requirements are high. Or eaten following exercise.

You will see from your list that carbohydrate foods are ranked as high or low GI or GL Try to choose most food from the low GI list. The GI only gives information about glucose, it should be used as a tool in combination with all you know from your own personal diet and training diary. A low GI food does not always mean that it is the healthiest choice, as it may contain fats and sugars other than glucose (fructose).

The insulin index provides further information as to the effects these carbohydrates have on insulin levels. You can use this and more importantly your own records of energy levels and food consumption to recognise foods which may cause peaks and troughs.

What You Can Do – General Guidelines

1. Avoid all processed carbs including all confectionery, honey, sweetened yoghurts, cereals, neat fruit juice and dried fruit. Replace refined carbohydrates (white bread, potatoes, pasta, and white rice) with unrefined carbs (whole grain bread, brown rice, fibrous vegetables, beans, etc).

2. Eat small frequent ‘mixed’ meals.

3. Always eat breakfast. Skipping breakfast results in low blood sugar for an extended period of time, your symptoms will worsen and compensatory eating will often be excessive, due to hunger.

4. Watch for ‘hidden’ sugar carefully. Read labels! Avoid those foods with modified corn starches or syrups. These are the hidden refined sugars!

5. Dilute all fruit juice 1:5 with water.

6. High Fibre Foods. Those vegetables growing above ground and whole grains tend to have a good fibre content. Fibre slows the absorption of sugar from the gut, by decreasing gastric emptying and glucose uptake. Cooking root vegetables (carrots and potatoes) alters their structure making the sugars more rapidly absorbed.

7. Increase the intake of quality protein foods (i.e. fish, poultry, lean meats, vegetarian proteins like tofu or tempeh). Protein is very effective at controlling appetite and also slows absorption of carbs when they are eaten together. Protein is also required to build lean muscle so it should appear in every meal.

8. Decrease your intake of soft fruit (oranges, grapes, plums, bananas etc) to 1-2 pieces a day. Dried fruit is particularly dense in sugars. Fruit should be 1/3 of your total vegetables and fruit intake and you should aim for 9 portions each day, 6 veggies and 3 fruit.

The Glycemic Index of Foods

The foods with the greatest effect on blood sugar have the highest scores

More GI values can be found at

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