Insulin Resistance and Type 2 Diabetes
Diabetes is a worldwide epidemic that is rising at a terrifying rate. The number of adults living with diabetes globally was estimated at 422 million in 2014, compared to 108 million in 1980 - an increase of almost 400% <1>. Even with adjustments for our ageing population, the global prevalence of diabetes has nearly doubled. If that isn’t daunting enough, the number of adults living with diabetes is projected to reach an unimaginable 592 million in 2035 <2>. In Australia alone, 5 in every 100 people have a known diagnosis of diabetes <3>. That’s 1 in every 20 families.
What is Diabetes?
There are many different types of diabetes, including type 1, type 2, and gestational diabetes. Though the cause and contributors of these forms of the disease vary greatly, with some being unknown, the underlying mechanism of diabetes is the same. Diabetes describes the inability of a person to tolerate carbohydrate. Just like any other food intolerance, individuals with diabetes have varying degrees of carbohydrate tolerance, and this can change over time with the progression (or regression) of their disease. For clarity, the focus of this article is primarily on type 2 diabetes and insulin resistance.
When any person consumes a meal containing dietary carbohydrate, their digestive processes break this carbohydrate down into molecules of glucose. Glucose is also commonly termed “blood sugar”. Glucose then travels through your bloodstream to reach the many billions of cells in your body and provide them with a substance that is used for producing energy. However, glucose cannot freely cross cell membranes and must enter via a lock and key system. Imagine there are lots of tiny doors on the outside of your cells (Figure 1). This might be any type of cell - a liver cell, a fat cell, a muscle cell, etc. The key to unlocking these doors and allowing glucose to enter is a hormone called insulin. The pancreas produces insulin in response to rising blood glucose levels (Figure 2) and insulin unlocks the doors so glucose can access the cell and be removed from the blood. Inside the cell, glucose is used as energy or stored as fat or glycogen (Figure 3).
Though glucose is a fantastic source of energy, it can also be extremely damaging if it is left to roam around the blood for too long (hyperglycaemia). Imagine glucose as a sticky molecule, like glue. When there is too much of it in your blood and/or it hangs around in the blood for too long, glucose starts sticking to the proteins and lipids in your body and impairs their function. This hazardous process is known as glycation and can negatively affect many systems in your body. For example, Figure 4 shows how glucose can react with collagen (protein in the skin) and accelerate the ageing process. This is one of the main reasons why our body has an elegant system in place to ensure the level of glucose in our blood is brought back to about one teaspoon (~5 mmol/L) as quickly as possible after meals (i.e., Figures 1-3).
The consequences of poorly managed diabetes and hyperglycaemia go far beyond brittle skin, with diabetes being a major cause of morbidity and mortality. Acute complications of diabetes include ketoacidosis and hyperosmolar coma. Chronic complications typically result from damage caused by excess glucose and/or insulin levels in the blood and develop over a much greater period. Chronic diabetes complications include cardiovascular disease (e.g., heart attack, stroke), nephropathy (kidney disease), peripheral neuropathy (nerve damage) and retinopathy (eye damage). In 2012, diabetes caused 1.5 million deaths, and complications relating specifically to hyperglycaemia caused an additional 2.2 million deaths <5>.
Insulin resistance begins many years before the diagnoses of type 2 diabetes. Insulin resistance describes a state where the insulin keys are not quite fitting the locks on the cell doors as well as they used to. In its early stages, the body compensates by producing more insulin to keep blood glucose within the normal range. However, over time the body has to produce more and more insulin to prevent glucose from building up in the blood stream. Without effective action, insulin resistance can worsen to the point where the body is no longer able to keep up with the demand from incoming glucose, resulting in hyperglycaemia (Figure 5). It is generally recognised that anyone with a fasting or random blood glucose level below 5.5 mmol/L is healthy and free from diabetes. However, blood glucose testing does not account for the extra insulin that may be circulating in one’s system and insulin resistance can easily be missed. Insulin testing (in combination with glucose testing) offers clinicians a window for early detection of insulin resistance and/or prevention of type 2 diabetes.
Type 2 diabetes occurs when the pancreas can no longer keep up with the increased glucose demand and the body becomes insulin deficient. Relative insulin deficiency is when the pancreas is being overworked (Figure 5), while absolute insulin deficiency is when the pancreas has completely “burnt out”. Due to the epidemical nature of diabetes and its dire health outcomes, adults should pro-actively be requesting their doctors test them for insulin resistance every two to five years from the age of eighteen (preferably with an oral glucose tolerance test that includes insulin testing at fasting, 1 hour and 2 hours). A recent review of data from seven countries found that between 24% and 62% of people with diabetes were undiagnosed and untreated, and it is expected that a much greater proportion of people are walking around with insulin resistance and don’t know it <6>.
There are many potential causes and contributors of insulin resistance, with some of the main offenders being diet, visceral adiposity (fat around your organs), genetics, and age. Thyroid health also plays an integral role in one’s susceptibility to developing insulin resistance, considering that the thyroid is a major regulator of carbohydrate metabolism and pancreatic function <7, 8>. For example, low thyroid function (hypothyroid) can slow the response of insulin to elevated blood sugar and thus, the rate of glucose uptake by cells. However, this is not a one-way relationship. Diabetes and thyroid disorders have been shown to mutually influence each other and the repeated blood sugar fluctuations resulting from untreated insulin resistance can also negatively impact thyroid function <9>.
What is a High Blood Glucose Level?
Blood glucose can easily be measured using a glucometer, and typically involves testing blood that is drawn from a finger prick. Type 2 diabetes is diagnosed from a fasting blood glucose level of 7.0 mmol/L or above, or a random blood glucose level of 11.0 mmol/L or greater <10>. Insulin resistance is well and truly evident with impaired fasting glucose (fasting blood glucose level between 5.5 mmol/L and 6.9 mmol/L) or impaired glucose tolerance (blood glucose level between 7.0 and 11.1 mmol/L two hours after a carbohydrate-containing meal). Glucometers can be purchased at any chemist and are useful tools in helping individuals track their blood glucose levels.
Prevention & Management Strategies
Blood glucose levels are affected by multiple factors including diet, illness, stress and exercise. Though all factors must be taken into consideration, dietary carbohydrate has the most significant impact on blood sugars. However, the answer to achieving normal blood glucose levels is not necessarily to eliminate all dietary carbohydrate. Carbohydrate is found across all major food groups, including bread, cereals, vegetables, beans, fruit, dairy, nuts and seeds. A low-carbohydrate diet that includes non-starchy vegetables, high-quality proteins and healthy fats is an appropriate and well-researched strategy. With the consideration that individuals have varying levels of carbohydrate tolerance, it is useful to work with a qualified health practitioner who can help you determine the level of carbohydrate that is right for you and safely adjust any medications if required. A dietitian experienced in low-carbohydrate nutrition can help you formulate a nutritionally adequate diet with appropriate levels of carbohydrate, protein and fat.
Though type 2 diabetes is a serious and widely prevalent disease, there is a range of effective nutritional and medical strategies that can be harnessed to empower and support affected individuals. I believe that it is possible for an individual with compromised carbohydrate tolerance to achieve normal blood glucose levels and live a long, happy and healthy life.
By Jessica Turton
Accredited Practising Dietitian (APD) Jessica.firstname.lastname@example.org