Exercise and Type 2 Diabetes

Type 2 Diabetes is being diagnosed with increasing measure. In 2008 it was estimated that 347 million or 5% of the population had diabetes, this has increase from the estimated 153 million cases in 1980 (1). WHO estimates that Type 2 Diabetes makes up 90% of these cases. Diabetes is a serious condition when left untreated and can greatly impact on an individuals health and quality of life. In those with Diabetes life expectancy is significantly reduced due to an increased prevelance of heart disease and stroke occurance. The rise in the incidence of the disease has coincided with societies technological advancement. Lower levels of physical fitness along with a sharp rises in obesity levels has led to the spike in the incidence of this disease. 

What is Type 2 Diabetes?

Type 2 Diabetes is a disease related to the inability to effectively control blood glucose levels. In healthy individuals blood glucose levels are held relatively constant. This is achieved through endocrine hormones,  insulin is the primary hormone involved in lowering blood glucose. Insulin aids the transport of blood glucose into the muscles and liver cells. In Type 2 Diabetes blood glucose is unable to be effectively transported into muscle and liver tissue. The result is blood Glucose levels rise resulting in damage to blood cells and nerve tissue. 

This high blood Glucose is called Hyperglycemia. Prolonged hyperglycemia increases the risk of heart disease, stroke, infection and nerve damage. (see diagram below)

Diagnosis

Type 2 Diabetes can be diagnosed using a fasting blood glucose test, a standard non fasting blood glucose test and a glycated haemoglobin test (A1C)

Understanding Blood Glucose in the Body

Carbohydrate intake and Blood Glucose

Foods are made up of macronutrients called Carbohydrates, Fats and Proteins. These macronutrients supply the body with the energy it requires to function. When food containing Carbohydrates is consumed the carbohydrates are absorbed in the digestive track and enter the blood stream as a molecule called Glucose. Glucose levels in the blood vary only slightly and total approximately 5 grams in the average adult. A typical meal contains 40-80grams of carbohydrates. At rest the carbohydrates in the meal are absorbed faster then they are utilized. As a result glucose must be stored before the blood glucose level rises beyond safe levels.

Glucose Storage

Glucose that is not being used by muscle cells, the brain or other organs is stored in the liver and muscles tissue as glycogen. The approximate level of Glycogen (stored glucose) found in the liver is 100 grams with the amount varying between individuals. Muscle tissue stores are estimated at between 200 - 500 grams

Muscle and Glucose use

Muscles are made up of proteins which contract  in order to produce movement. Inorder for these contractions to occur a molecule called ATP is required. During contraction ATP is broken down and as a result needs to be restored. The restoration of ATP levels within the body is fundamental to being able to produce continued movement. This restoration requires fuels or energy from within the body. Glucose which is a simple form of carbohydrate along with stored fats are the primary source of this fuel.

Health Implications of Diabetes

Diabetes results in an increased incidence of heart disease. Heart disease is the number one cause of premature death in Australia. Elevated blood glucose levels increase damage to blood vessel walls which results in accelerated atherosclerosis. Atherosclerosis is the fatty build up of plaque found in the arteries. This build up causes blockages similar to that seen in a water pipe. The result is, blood cannot reach the desired tissues, which starves the tissue of oxygen. If oxygen fails to reach the heart you'll experience what is called a heart attack, if oxygen fails to reach the brain this is called a stroke. For an article on the importance of oxygen in cells click here

Elevated Blood Glucose also causes nerve damage. Our Nerve cells are like electrical wires. They carry signals from the brain to the muscles. This is how we produce movement. They also carry feedback from the nerves in the body to the brain. This is how we feel heat, cold, pain, touch and move in a coordinated manor. Damage to nerve fibres is mostly irreparable as nerve cells grow and repair at slow rates and in some cases they fail to recover at all. For this reason keeping blood glucose levels in the desired range is of great importance. For more information on diabetes and nerve damage see http://diabetes.niddk.nih.gov/dm/pubs/neuropathies/

Causes of Type 2 Diabetes

Diabetes in the most part is considered a lifestyle disease. This means lifestyle factors are the primarily contributer to the disease. 

The mechanism causing Type 2 Diabetes is still under investigation. Diabetes causes a decrease in insulin sensitivity. Insulin is the hormone that results in Glucose being taken from the blood and into the muscle tissue to be later used. Having a decreased insulin sensitivity results in higher insulin levels inorder to lower blood glucose levels. The exact cause of this insulin insensitivity is still debated.

Some of the contributing factors are Physical Inactivity, Excess Body Weight, High Cellular Triglyceride (fats) stores and and having a poor Aerobic Fitness level.

Physical Inactivity and Diabetes Risk

Physical inactivity is a cause of decreased insulin sensitivity. During exercise muscle and liver glucose levels decrease resulting in an increased post exercise uptake of glucose into your cells. This can last for 24-48 hours after the exercise. Studies show that those who are physically active have a lower incidence of diabetes. A study of 87000 women over 8 years showed those who exercised vigorously once per week had .67 times the risk of developing diabetes then those who did not (2). That means a one third reduction from one exercise session a week.

A study of male physicians showed a .77 times risk for those exercise once, a .62 time risk for those exercising 2-4 times a week and a .58 risk for those exercising 5 times per week (3). See Figure Below

A study of 7700 men found that those who exercised regularly had a .4 times risk of developing diabetes. (4)

Body Weight and Diabetes Risk

Body weight is more important then physical activity when looking at diabetes. Diabetes is a disease related to energy storage and the heavier the individual the greater there risk of developing the disease. A study of 20000 college students looked at each individuals level of weight gain over 27 years (5). They found that students who gain 9kg or more over this period had a 7 times greater incidence of Diabetes then those who gained only 1.5kg's. See graph for the risk associated with weight gain. Click for more Information on Weight Gain and Health

Diet and Diabetes Risk

The long term effects of diet on Type 2 Diabetes is not completely understood. Following dietary guideline which produce weight loss will have a beneficial effect in preventing Diabetes as weight gain is the primary risk factor. Some healthy eating guidelines for weight loss are listed below

1. Consume fibrous foods
2. Eat a moderate protein intake
3. Reduce Energy Dense Foods
4. Eat wholegrain foods
5. Consume a low to moderate fat intake
6. Avoid excess sugar in the form of additives and excessive fruit consumption
7. Consume low GI carbohydrates
8. Drink adequate water

See also Guidelines for eating for weight loss

Excess fat intake in the diet has been shown to decrease insulin sensitivity. The high fat content may work at a cellular level to prevent glucose being used in the muscles effectively.

High sugar intakes such as those found in soft drinks, lollies, cakes, and many cereals or even high fruit intakes can lead to insulin insensitivity. Sugar is converted to fats by the liver and causes a rise in blood triglyceride. High fructose diets, the type of carbohydrate found in table sugar and fruit has been shown to decrease insulin function (6, 7)

Fructose is metabolised differently to glucose, this difference may result in excessive weight gain and cause metabolic changes at the muscle resulting in diabetes progression

Fitness Level and Diabetes Risk

Aerobic fitness level is related to the risk of developing diabetes. The higher the persons fitness level the lower their risk of developing the disease. The Multi stage Beep Test and the 2.4km Run Test are two common ways of measuring your aerobic fitness level. For more infomation on aerobic fitness and disease see aerobic fitness level, health and disease.

A 14 year follow up study of 4,747 men showed those in the highest quarter for aerobic fitness had one forth of the cases of diabetes then those in the lowest fitness level (8). Having a higher aerobic fitness level indicates are higher capillary density and possibly a greater percentage of type 1 muscle fibres. Both these variables are correlated to a lowered diabetes risk

Prevention of Type 2 Diabetes

Diabetes intervention studies show large levels of success with diet and exercise interventions. 

Interventions which increase the amount of exercise a person completes or cause a resultant weight loss will have a beneficial affect for those with Type 2 Diabetes.

http://diabetes.niddk.nih.gov/dm/pubs/preventionprogram/

Preventing diabetes requires maintaining correct body weight, exercising aerobically, maintaining muscle mass through resistance or interval training and eating a diet that is not high in fat or sugars.