Wednesday, 27 May 2015

Insulin


In an earlier article I talked about the importance of focusing on nutrient density and quality and not just calories.  The first law of thermodynamics essentially boils down to:

Energy in (from food)-energy burned (physical activity and other metabolic processes) = energy balance

So if energy balance is positive, we gain weight and if it’s a negative we lose weight.  This has been the basis for many nutritional programmes whether the aim is to gain or lose weight.  I'm not here to argue with this rule as it’s completely correct, we must consider caloric intake for nutritional strategies.  What I do want to discuss is another major consideration we need to make when it comes to the food we eat.  The biological processes in our body are regulated by a number of hormones, and it’s important to understand these hormones and their functions for health, body composition and performance.  I am a strong believer that a better understanding of our bodily processes will lead to us making more positive diet and lifestyle choices.  In short knowledge is power. 
A hormone that most people will recognise is insulin.  Insulin one of the hormones responsible for the metabolism of carbohydrate, amino acids and fats.  It is a peptide hormone that is produced in the beta cells in the pancreas.

How it works
When carbohydrate is digested it enters the blood stream, this triggers both the synthesis and secretion of insulin from the beta cells.  To go a little deeper into the mechanism glucose in the blood stream stimulates calcium ions to move into the beta cells, thus triggering a calcium-dependant exocytosis of insulin through microtubules releasing it into the blood stream.  Amino acids, particularly leucine, fatty acids and ketone bodies have all been shown to exert a weak stimulation of insulin secretion, however these are dependent on the presence of glucose in the blood to be effective.
Insulin has many functions, however its main role is to act as a transporter for glucose into cells.  Glucose is an energy source for all cells in the human body.  Skeletal muscle, cardiac muscle and adipose (fat) tissue are heavily reliant on insulin to deliver the glucose they require.  Insulin stimulates the translocation of glucose transport type 4 (GLUT 4) from within cells to the outside membrane allowing it to accept glucose and transport it into the cell.
So when we consume carbohydrate, blood glucose levels rise, insulin is secreted and glucose is taken up by the cells to be used as energy.  The body is constantly working to maintain a stable blood glucose level of around 4mmol/l.

Diabetes
The condition most associated with insulin is diabetes.  There are two main types of diabetes type 1 and type 2.

Type 1 is characterised by a loss of beta cells in the pancreas therefore reducing the organs ability to secrete insulin.  The condition is usually a result of an autoimmune reaction.  It generally develops in childhood or early adulthood, and requires treatment with exogenous (from outside the body) insulin.

Type 2 occurs as a result of cells becoming insulin resistant, which I will go on to explain in more detail.  It normally presents in adulthood, however it is becoming more frequently diagnosed in children.   Type two diabetics can sometimes go on to require insulin to manage their condition.  Type 2 diabetes makes up around 90% of all cases of diabetes.

Glycemic Index and Glycemic Load
When discussing insulin and nutrition glycemic index and glycemic load is often brought up.  According to Diabetes UK the glycemic index is “A ranking of carbohydrate-containing foods based on the overall effect on blood glucose levels. Slowly absorbed foods have a low GI rating, while foods that are more quickly absorbed have a higher rating.”  The scale goes from 0-100 with pure glucose being 100.  They define glycemic load as “A measure that takes into account the amount of carbohydrate in a portion of food together with how quickly it raises blood glucose levels.”  I quite like this is a measure, as it considers both the type of food and the portion size.  A low glycemic load is between 0-10, medium 11-19 and anything above 20 is considered to have a high glycemic load

Insulin Sensitivity/Resistance
So I have already mentioned the term insulin resistance so let’s delve into what it is.  Insulin resistance is a state in which the cells response to insulin is impaired.  As a result glucose cannot enter the cell and blood sugar levels remain elevated.  Now because blood glucose levels remain high the body reacts by creating and secreting more insulin, so now we have elevated levels of both blood glucose and insulin (hyperinsulinemia).  The pancreas will continue to release insulin until blood sugar levels drop back down to within normal limits.  With insulin resistance it’s not a case of you have it or you don’t, individuals will vary on a scale between being insulin sensitive and insulin resistant.  When someone has high insulin sensitivity it’s like insulin is communicating with the cells on the latest 4G smartphone, whereas being insulin resistance is not unlike the two bean cans tied together with string.  I should also point out our insulin sensitivity varies depending on a variety of factors including time of day, diet and training stimulus.

Insulin resistance is associated with an increased risk of a number of health conditions including diabetes, hypertension, atherosclerosis (a precursor to coronary heart disease), obesity and polycystic ovaries.

There are several genetic risk factors for insulin resistance, however diet and lifestyle plays a huge role in both the development and management of the condition.  Being overweight or obese and/or having a diet high in refined carbohydrate significantly increase the risk of an individual becoming more insulin resistant.  In terms of prevention a healthy balanced diet with an emphasis on single ingredient whole foods, alongside regular activity is certainly the way to go.  When an individual is already to some degree insulin resistant the dietary strategy becomes a little more complicated and debated.  Most recommendations are that when consuming foods rich in carbohydrate aim for those with a lower glycemic index (e.g. brown rice, beans, pulses and oats).  There is also evidence to support the use of low or moderate carbohydrate diets to manage and even reverse insulin resistance.  The purpose of this article is not to debate the varying dietary strategies, if you or someone you know is found to be insulin resistance or diagnosed as pre-diabetic, advice should be sought from primary care providers as dietary strategies should be ideally tailored on an individual basis.
Low Glycemic Index Foods
So to sum up here what we generally want is to maintain a high degree of insulin sensitivity and less insulin resistance.  To test for insulin resistance an oral glucose tolerance test can be performed.  This involves consuming a glucose drink in a fasted state and monitoring blood glucose levels before ingestion and 30, 60 and 120 minutes post ingestion.  The speed at which the body lowers blood glucose levels back to normal indicates how inulin sensitive or resistant an individual is.

Insulin as an Anabolic Hormone 
The final thing I wanted to touch on in regards to insulin is its use as an anabolic hormone.  Because insulin facilitates the transport of carbohydrate and amino acids into the cells it promotes an anabolic environment, as well as preventing catabolism.  It is essentially delivering your muscles the fuel they need to perform, recover and grow.  Strategically manipulating insulin is something body builders and athletes have been doing for years.  This is normally achieved by consuming fast acting (high GI) carbohydrate before and/or after work outs.  Now I would be completely naive to ignore the fact that insulin abuse is a problem in the body building community.    To take advantage of the anabolic properties of insulin some body builders give themselves insulin injections.  It’s certainly not something all of them do, however a survey of 450 body builders found that 10% admitted to abusing insulin.  This is extremely dangerous, it can cause hypoglycaemic events, pancreatitis, coma and even death.  So unless you require insulin for a medical reason, the risk of injecting more far outweighs any potential benefit.

So there we have a quick whistle stop tour about insulin and its role within the body.  Hope you enjoyed it.

References

Accurso, A., Bernstein, R., Dahlqvist, A., Draznin, B., Feinman, R., Fine, E., Gleed, A., Jacobs, D., Larson, G., Lustig, R., Manninen, A., McFarlane, S., Morrison, K., Nielsen, J., Ravnskov, U., Roth, K., Silvestre, R., Sowers, J., Sundberg, R., Volek, J., Westman, E., Wood, R., Wortman, J. and 
Vernon, M. (2008). Dietary carbohydrate restriction in type 2 diabetes mellitus and metabolic syndrome: time for a critical appraisal. Nutr Metab (Lond), 5(1), p.9.

Davies, A., Blakeley, A., Kidd, C. and McGeown, J. (2001). Human physiology. Edinburgh: Churchill Livingstone.

Diabetes.co.uk, (2015). Diabetes UK, UK Diabetes Resource, Diabetes Symptoms, Diabetes Diet, Gestational Diabetes. [online] Available at: http://www.diabetes.co.uk/ [Accessed 25 May 2015].

Evans, P. (2003). Insulin as a drug of abuse in body building. British Journal of Sports Medicine, 37(4), pp.356-357.

Fox, S. (1996). Human physiology. Dubuque, IA: Wm. C. Brown.

Kumar, P. and Clark, M. (n.d.). Kumar & Clark's clinical medicine.

Westman, E., Yancy, W., Mavropoulos, J., Marquart, M. and McDuffie, J. (2008). The effect of a low-carbohydrate, ketogenic diet versus a low-glycemic index diet on glycemic control in type 2 diabetes mellitus. Nutr Metab (Lond), 5(1), p.36.



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