INSULIN - THE BASICS | Optimal Nutrition Protocol

INSULIN – THE BASICS

Our body is regulated by a wide variety of hormones that ensure optimal functioning of the body.
What is insulin and what is its function?
Insulin is a hormone produced by the pancreas that is needed for the use or storage of body fuels (1). For this very reason, insulin is known as an anabolic hormone. Anabolic hormones are those that help in building new tissue. Insulin also regulates blood sugar levels in your body. For example, when you eat a meal, the meal is digested and broken down to glucose. In response to the rise in glucose, the pancreas secretes insulin which ensures the glucose enters the fat, muscle and liver. As blood glucose levels drop, insulin levels also respond similarly. 
In addition to regulating blood glucose, insulin also plays a role in the creation of fat and inhibits the breakdown of fat. This is the reason why insulin is feared by most, which will be addressed later on.

What is insulin resistance and insulin sensitivity?
Insulin sensitivity  tells us how sensitive the body is to insulin. This varies from person to person. Physical activity and eating choices have a positive effect in increasing insulin sensitivity. 
Insulin resistance is known as decreased responsiveness to insulin (1). That is, the tissues have decreased sensitivity to insulin. If the body is resistant to insulin, the body tries to counter the situation by producing more insulin. Insulin resistance can be caused by several factors including excess adiposity and even a sedentary lifestyle. Insulin resistance is also observed in those with Polycystic Ovarian Syndrome (PCOS).
Do carbohydrates spike insulin, and thus increases storage of fat?
This is the biggest myth with regards to insulin. Fat is created through a process known as lipogenesis and is broken down through a process known as lipolysis. Insulin is known to stimulate lipogenesis and inhibit lipolysis. This means that increased levels of insulin leads to fat storage right? Wrong. 
There exists another enzyme known as Hormone Sensitive Lipase (HSL) whose main function is to break down stored triacylglycerols in the adipose tissue i.e., lipolysis (2). Insulin inhibits the action of HSL. So once again, increased insulin levels must be the issue right? What is interesting to note here is, even consumption of fat can suppress HSL activity (3), when insulin levels are low in the body. The study concluded that insulin was not needed to suppress HSL. Hence, if you are overeating beyond your required energy intake, you will still not see weight loss changes, despite insulin levels being low.
Does only carbohydrate stimulate insulin release?
In healthy individuals, insulin is released in response to meals.  Infact, only few people are aware that protein stimulates insulin too! A study by Boelsma et al. (4) measured the insulin response to two meals,one Low Protein High Carbohydrate (LP/HC) and the other High Protein Low Carb (HP/LC). They found that the protein rich meal stimulated insulin as well!
Another study (5) assessed the insulin response of four different types of protein shakes, egg, tuna, whey and turkey. They found out that the insulin response was the highest after the whey protein meal. The whey protein shake also reduced appetite to a greater extent compared to the rest of the test shakes. 
How does insulin play a role in diabetes?
Diabetes is classified into two types;
Type 1 diabetes: In this case, the pancreas does not produce insulin or is producing very little. We know insulin is needed to regulate blood sugar levels, So in this case, blood sugar builds up in the bloodstream, which can be dangerous to health. This is also known as juvenile diabetes.
Latent Onset Type 1 diabetes: This is a condition that presents itself in adulthood. This is characterised by insulin requirements to treat hypogylcaemia and prevent ketogenesis (6).
Type 2 diabetes: The cause for type 2 diabetes is most likely associated with Insulin Resistance. As a result, the pancreas secretes more insulin like mentioned before. This increases blood sugar leading to prediabetes and consequently diabetes. 
There are several diet plans focussing on lowering carbohydrate intake in order to ensure that insulin levels are normal. These plans are rigid and keep carbohydrates to a bare minimum, while focussing on fat and protein intake. Little are they aware that protein spikes insulin too! Besides, the actual issue to address is the overall diet and other behaviour modifications of the individual. This along with adherence will ensure a sustainable lifestyle to follow.

References:

1) Mahan L, Raymond J. Krause’s food & the nutrition care process. 14th ed. Elsiever.
2) Kraemer F, Shen W. Hormone-sensitive lipase. Journal of Lipid Research. 2002;43(10):1585-1594.
3) Evans K, Clark M, Frayn K. Effects of an oral and intravenous fat load on adipose tissue and forearm lipid metabolism. American Journal of Physiology-Endocrinology and Metabolism. 1999;276(2):E241-E248.
4) 10. Boelsma E, Brink E, Stafleu A, Hendriks H. Measures of postprandial wellness after single intake of two protein–carbohydrate meals. Appetite. 2010;54(3):456-464.
5) Pal S, Ellis V. The acute effects of four protein meals on insulin, glucose, appetite and energy intake in lean men. British Journal of Nutrition. 2010;104(8):1241-1248. 
6) Lasserson D, Fox R, Farmer A. Late onset type 1 diabetes. BMJ. 2012;344(apr30 1):e2827-e2827.

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