Diabetes refers to a group of conditions characterized by high levels of blood glucose, commonly
known as blood sugar.
Glucose comes from digestion of carbohydrates in food, and is carried by the bloodstream
to various body tissues.
But glucose cannot cross the cell membrane to enter the cells on its own; to do so, it
requires assistance from a hormone produced by the pancreas called insulin.
Binding of insulin to its receptor on a target cell triggers a signaling cascade that brings
glucose transporters to the cell membrane, creating passageways for glucose to enter
the cells.
In most tissues, muscles for example, glucose is used as an energy source, while in the
liver and adipose tissue, it is also stored for later use, in the form of glycogen and
fats.
When the body is in the fasted state, the liver produces and secretes glucose into the
blood, while adipose tissues release free fatty acids to the liver where they are converted
into additional metabolic fuel.
Diabetes happens when insulin is either deficient or its action is compromised.
Without insulin, glucose cannot enter the cells; it stays in the blood, causing high
blood sugar levels.
There are 2 major types of diabetes.
Type 1 is when the pancreas does not produce enough insulin; and type 2 is when the body’s
cells do not respond well to insulin - they are insulin-resistant.
Both types are caused by a combination of genetic and environmental factors but genetics
plays a major role in type 1, while lifestyle is a predominant risk factor for type 2.
For this reason, type 1 diabetes usually starts suddenly in childhood, while type 2 progresses
gradually during adulthood, going through a so called pre-diabetic stage, which is defined
as borderline blood sugar levels: higher than normal, but lower than diabetic.
Pre-diabetes is very common, and while not always developing into full-blown diabetes,
over time, it can cause much the same damage to the body.
Unhealthy lifestyle is the trigger of pre-diabetes and the main driving force behind its progression
to diabetes type 2.
The key factors are obesity and physical inactivity.
There are at least 2 ways by which obesity can cause insulin resistance and high blood
glucose.
First, in obesity, fat cells have to process more nutrients than they can manage and become
stressed.
As a result, they release inflammatory mediators, known as cytokines.
Cytokines interfere with the signaling cascade by insulin receptor, blocking the action of
insulin, thereby causing the cells to become less responsive to insulin.
Second, excess adipose tissue releases abnormally large amount of free fatty acids to the liver
– an event that normally happens only when the body is fasting.
This tricks the liver into producing and releasing more glucose into the blood.
High blood glucose stimulates further insulin secretion.
Constant high insulin levels de-sensitize body tissues, causing insulin insensitivity.
Intra-abdominal fat appears to produce more fatty acids and cytokines, and therefore has
more severe effect on blood glucose, than subcutaneous, or peripheral fat.
For this reason, large waist size is a greater risk factor than high body mass index.
Sedentary lifestyle, apart from having indirect effect by causing weight gain, has its own
direct impact on insulin resistance.
This is because physical activity is required to maintain healthy blood sugar levels.
Physical activity increases energy demand by the muscles, which consume glucose from
the blood, and subsequently from glucose storage in the liver and adipose tissue.
High energy expenditure helps to clear up faster the spikes of blood glucose that follow
every meal.
High energy demand also promotes better cellular response to insulin, increasing insulin sensitivity.
Studies have shown that physical inactivity, even for a short period of time, results in
consistently higher spikes of blood sugar after meals, which can trigger pre-diabetic
changes in healthy individuals, or speed up transition from pre-diabetes to diabetes.
More importantly, this happens not only to over-weight patients, but also to people with
seemingly healthy weight.
This is probably because inactivity reduces muscle mass and replaces it with adipose tissue,
thus having serious effects on blood sugar levels while still maintaining an overall
normal weight.
The bottom line is, in order to prevent diabetes, weight management must be combined with physical
activity or exercise.