What is Insulin?
Insulin hormone; a peptide hormone secreted by Beta cells of pancreatic islets of Langherhans, functions to make sure that the glucose released in blood after consuming food is absorbed by liver, muscles and the adipose tissue thereby managing the blood glucose level to their desired range.
Insulin hormone is responsible for carbohydrate metabolism, lipid metabolism and protein synthesis at a cellular level. It is the dominant hormone drawing these activities and it works in sync with the growth hormone and IGF-1, GLUT-4 while the body is in a fed state. Glucagon along with other glucacortichoids and catecholamines work counter-productive in a fasted state to insulin (often termed as antagonist hormones).
Often demonized as a catabolic hormone, insulin on the contrary can be highly anabolic if the nutrition and expenditure are maintained in the right manner. It is highly anabolic along with the growth hormone, IGF-1 and sufficient amino acids.
Understanding Insulin Resistance:
The most basic explanation of insulin resistance (IR) is when the body is not able to use the insulin secreted by pancreas for managing the blood glucose levels. It is a condition when cells in our muscles, fat, and liver do not respond well to insulin and can’t easily take up glucose from blood; in short they become resistant to insulin. This can also be termed as an impaired sensitivity to insulin.
Muscles, Adipose tissue & IR: In case of IR, the muscle glycogen synthesis is impaired primarily because glucose uptake of muscles is highly dependent on insulin. In case of adipose tissue, the intracellular glucose transport into adipocytes or the fat cells in the fed state are insulin-dependent via GLUT 4. Insulin promotes lipogenesis and suppresses lipolysis. This in turn reduces free fatty acids in blood stream thereby maintaining cholesterol levels. However in IR, the liver shows an increased fatty acid flux which tends to increase / promote VLDL production.
Macronutrients and IR: In terms of macronutrients, carbohydrates and protein are major insulin secretion stimulators. High fat diets – particularly high in saturated fats also tend to spike insulin secretion. The spike varies but they all can stimulate secretion. However dietary fibers do not have a direct effect on insulin secretion. Among others, alcohol consumption has also been seen to stimulate insulin secretion.
IR and its effects: The major clinical syndromes associated with IR are Pre-diabetes and type 2 Diabetes.
Pre-diabetes is a condition where blood sugar levels are higher than usual but not very high to be prescribed as type 2 diabetes. This can arise either if a person is insulin resistant or the beta cells of pancreas are not making enough insulin to normalize the blood glucose levels. The condition is more common to obese or overweight individuals, people with a family history of diabetes, sedentary lifestyle, PCOD and PCOS suffering females or individuals with cardiac issues.
IR or Pre-diabetes are generally asymptomatic. However in due course of time, it can very well result in retinopathy – which is more common in people suffering with type 2 diabetes (T2DM). People with diabetes can also have many other criticalities other than just retinopathy. Renal functions are also affected in due course of time with people suffering with diabetes. A lot of times, this is characterized as Insulin resistance syndrome which describes a cluster of abnormalities associated with individuals facing IR. IR also stimulates metabolic syndrome which is associated with lipid profile of the body, thereby responsible for cardiac health in long term.
IR and pre-diabetes are generally diagnosed with blood tests while measuring fasting plasma insulin. HbA1c test is another clinical method which gives a cumulative of past 3 months of glucose levels in the body.
IR inhibits various metabolic pathways like glucose transport, glycogen synthesis and also anti-lipolysis action. It can further result in T2DM, hypertension, dyslipidemia, non alcoholic fatty liver disease (NAFLD), fibrinolysis, PCOS, OSA etc. These can also result in cardiovascular diseases going forward. But the most common cause of IR by far are obesity and increased free fatty acids in the plasma.
This is where a negative energy balance to maintain a healthy weight range and an exercise routine to increase energy expenditure comes in the picture – in order to combat IR or maintain the disorder at lowest extremes.
Glossary:
IGF-1: Insulin-like growth factor 1, works as a major growth factor, IGF-1 is responsible for stimulating growth of all cell types and causing significant metabolic effects – Produced primarily by liver.
GLUT-4: Glucose transporter type 4, insulin regulated glucose transporter, primarily found in adipose tissues and striated muscles.
Glucacortichoids: Class of corticosteroids that work against inflammation (immune system) and certain allergies.
Catecholamines: Released by adrenaline, working for flight or fight response of the body (response to stress).
Dyslipidemia: Abnormally elevated cholesterol or fats (lipids) in the blood.
Fibrinolysis: Fibrinolysis is a process that prevents blood clots from growing and becoming problematic. Primary fibrinolysis is a body process, however secondary is when the clots are broken down under the effect of medication, disorder or underlying causes.
OSA: Obstructive Sleep Apnea (OSA) is a disorder caused by the repetitive collapse of the upper airway during sleep, snoring being often associated with it.
Sources:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3169796/
