as seen in people who have type I diabetes: they can’t produce insulin so they need to regularly inject themselves with this hormone. Without these injections their blood sugar level would be too high which has serious and indeed fatal consequences. So, as with many things in life, it is a question of balance: too much or too little insulin in the body are just as dangerous for your health.
What exactly does insulin do?
Insulin is one of many hormones in the body, and is also a protein. It is made in and secreted from cells in the pancreas called the Islets of Langerhans, named after the German pathologist who discovered them. The pancreas is one of the most important organs involved in digesting food and storing the nutrients in what you eat in your body’s cells. To give you an idea of proportion, about 98 per cent of the cells of the pancreas are devoted to digestion, with the Islets of Langerhans cells accounting for the remaining 2 per cent. The cells in the Islets of Langerhans that produce insulin are called beta cells, or B-cells. There are also alpha cells, or A-cells, which produce glucagon, a hormone that raises blood glucose levels.
Insulin and carbohydrates
Insulin’s main function is storing glucose from the bloodstream into cells. This first involves converting glucose released into the bloodstream from the digestion of foods into glycogen. The body only has a limited capacity to store glycogen – the primary stores of glycogen in the body are the liver and muscles – so all other glucose is then stored as fat, known as adipose tissue. People who have Insulin Resistance typically store this fat around their middles. Either way, insulin lowers the concentration of glucose in the blood.
Insulin and proteins
Insulin doesn’t just determine what happens to the carbohydrates that we eat, it also plays an important part in the way that proteins are metabolized. During the digestive process, many proteins are broken down into amino acids, which are then transported into the bloodstream. Insulin promotes the transport of amino acids into the liver and muscle cells. In this way it is involved in storing proteins away in the body, just as it does carbohydrates. It also inhibits the breakdown of protein in muscle for fuel. This is because if insulin is present, the body concludes that there is adequate glucose available and there is no need to break down muscle proteins for energy.
Insulin and fats
Similarly, insulin also has command over how fats are handled in the body. It inhibits the release of fats from fat tissue. This means that insulin prevents the use of your fat for energy in a similar way to how it prevents your body breaking down proteins. Insulin also promotes the production of fatty acids in the liver, which increases the amount of fats (bad cholesterol and triglycerides) circulating in the bloodstream – a potential risk for heart disease when present in excess.
Essentially, what all this means is that insulin prevents the body from overly using itself up and breaking down structural proteins and fats, especially if you do not eat enough food. Obviously this worked well when we were hunter-gatherers, as it meant the body did not begin breaking down its reserves at the first sign of hunger. These days, few of us go hungry for any length of time, so insulin’s supreme ability to store glucose at fat for future use is not nearly so important. Indeed, the modern diet that encourages high insulin levels means that the body stores more glucose as fat and we are at greater risk of becoming overweight and obese.
How much insulin your body releases depends on what you eat
Under normal conditions, insulin is produced moments after we eat something, so insulin levels will always be higher after we eat than before. As our blood glucose levels increase, the pancreas secretes insulin into the blood and insulin then performs the storage roles described above. The rate at which the blood glucose level increases is primarily determined by the amount of carbohydrate you eat. The volume of amino acids (proteins) you eat also has an effect on insulin production but much less than carbohydrates. If you eat a portion of carbohydrates, for example, this raises your blood glucose far than if you ate the same amount of protein, resulting in more insulin being released to store the glucose away. Once the glucose and amino acids are stored away, levels of insulin reduce accordingly. In this way, insulin levels vary throughout the day depending on the food we eat.
Insulin Resistance
If the body is continuously exposed to high levels of insulin, the insulin receptor cells in the liver, adipose (fat) tissue and muscle start to become inefficient. The way insulin binds to the receptors in the liver, fat and muscle tissues becomes partially blunted. In essence, this means some tissues in the body become resistant to the effects of insulin so that insulin is not able to carry out its normal role. The body recognises that there is too much glucose in the bloodstream so the pancreas produces even more insulin to try and compensate. When your body is consistently producing high levels of insulin it is a sure indication that you are resistant to insulin, hence the term ‘Insulin Resistance’. The pancreas will ultimately become exhausted and unable to produce the insulin needed to maintain optimal glucose levels and this is when you become diabetic.
The harm Insulin Resistance does
We already touched on this in the introduction but it is worth looking at the knock-on health effects of Insulin Resistance in detail.
You may wonder why it is vital for the body to keep down glucose levels in the bloodstream. As much as we need glucose to function, glucose at too high a level leads to oxidation and this causes tissue damage. This is what happens in poorly controlled diabetes, which can lead to peripheral neuropathy, renal conditions and cataracts. Since high blood glucose is so damaging to your health, your body will do everything it can to maintain normal glucose levels. The only means the body has to do this is with insulin. As you will see, the list of health conditions associated with Insulin Resistance is long and unpleasant:
| Lay Description | Technical Term |
| Heart disease | Coronary Heart Disease (CHD) |
| Obesity | Body Mass Index (BMI) of 30 or over |
| Breast cancer | Breast Cancer |
| High blood insulin levels | Hyperinsulinaemia |
| High blood cholesterol levels | Hypercholesterolaemia |
