What is insulin?
- Hormone: a signaling molecule produced by the body or synthetically to control or regulate the activity of certain cells or organs
- Peptide: a small protein, a chain of amino acids (110 to be specific).
- Peptide hormones cannot pass easily through cell membranes (like steroid hormones can) and must bind to receptors on the surface of cell membranes to create the desired action.
- Anabolic: responsible for building (synthesizing) in the body, not breaking things down (which would be catabolic).
Where does insulin come from?
- The Pancreas
In an area of the pancreas called the Islet of Langerhans (I didn’t name it).
From Beta Cells in this area.
What causes insulin to be released from β-cells?
During digestion, nutrients from food, including fats, proteins, carbohydrates, and micronutrients, are broken down to their most basic forms and absorbed into the blood.
Ingestion of carbohydrates causes blood glucose levels to rise, and this is the primary trigger for insulin to be secreted from the pancreas into the blood stream.
Ingestion of certain amino acids can also trigger insulin release, but this is to a much smaller degree.
What does insulin do?
- Without insulin, glucose cannot get from the bloodstream into cells of the body. Insulin attaches to receptors on cell membranes and enables the transport of glucose into cells. Glucose gets transported mainly into skeletal muscle cells and fat tissue.
- Prioritizes the body’s use of carbohydrates as energy instead of fat or muscle.
- Insulin also causes cells to be more permeable to amino acids, creatine, and some minerals. In muscles, this helps with growth, repair, and energy.
- When insulin attaches to skeletal muscle it increases muscle protein synthesis (i.e. the building of muscle tissue from entering amino acids).
- Insulin causes blood vessels to dilate, increasing the amount of nutrients (glucose/amino acids) delivered to muscle cells.
What does the glycemic index have to do with insulin?
Foods are digested at various speeds, meaning their nutrients are absorbed into the bloodstream at different rates. The glycemic index (GI) is a reflection of digestion rate for carbohydrate sources. Higher GI numbers reflect faster digestion than lower GI numbers. High GI carbs arrive in the bloodstream quickly, driving blood glucose levels up high. Insulin spikes to make use of that glucose, but afterward blood glucose may crash to low levels causing fatigue (i.e. food coma). Low GI carbs gradually enter the blood stream, so insulin levels are more consistent.
Things that raise a carbohydrate’s digestion rate (higher GI): sugar
Things that lower a carbohydrate’s digestion rate (lower GI): fiber, protein
It’s generally suggested that at most times, one should consume lower GI carbohydrates. However, there are other times, such as after a strength training workout, where eating high-GI carbs with a whey protein shake (also quickly digested by the body) is optimal for increasing nutrient uptake into muscle tissue.
Why is insulin necessary?
There are a couple reasons insulin is important:
- Too much sugar (glucose) in the blood is toxic to the body. Blood glucose must remain within normal levels of 75-120ml/dl.
->As a side note: too little blood glucose is also problematic, but that’s an issue for another pancreatic hormone called glucagon.
- Glucose is an important energy source for our bodies’ daily processes. Without insulin, glucose can’t get into the cells to be used as energy. The body will deplete it’s glycogen stores and then break down muscle tissue for energy.
- Let’s not forget the brain. In the brain, insulin receptors are present in areas that control nutrient homeostasis (keeping nutrient levels constant), reproduction, cognition, memory, neural development, executive functioning, learning, and memory.
- I recall discussing the importance of glucose in the functioning of the hippocampus (a memory center in the brain) in my Psychology of Learning class at UCLA. My professor’s hypothesis (which he was testing on military members at Camp Pendleton) was that some symptoms of PTSD (inappropriate memory flashes) arise when, due to extreme emotional stress, the hippocampus depletes it’s glucose stores and cannot properly store memories.
Insulin Sensitivity vs. Resistance
These terms describe how sensitive the body is to the effects of insulin. When one is insulin sensitive, his or her cells respond properly to the presence of insulin. In cases of insulin resistance, cells fail to respond to the presence of insulin, blood glucose remains elevated, the pancreas releases more insulin, so blood insulin levels are also abnormally high.
Insulin resistance can be developed from diets that are chronically high in High-GI carbohydrates, and it can lead to the body’s inability to regulate blood glucose (Type 2 Diabetes).
Insulin sensitivity is considered a desired trait for good health, and it can be increased by both aerobic and anaerobic exercise. Maintaining insulin sensitivity can help with workout goals in a couple ways:
- More carbohydrates can get into the muscles during exercise allowing for better workout performance (because more energy!).
- Elevated insulin from eating or drinking carbohydrates post-workout increases amino acid uptake (building blocks for new muscle or muscle repair). It also enables faster recovery from workouts since muscle can quickly absorb glucose from the blood instead of the slow process of getting it from fat stores.
Sugar the Sweet Truth by Bret Contreras
Insulin by Rehan Jalali
The Muscle Building Messenger Complete Guide to Insulin by Jim Stoppani
 Goulet, E.D., Melancon, M.O., Aubertin-Leheudre, M., Dionne, I.J. (2005). Aerobic training improves insulin sensitivity 72-120h after the last exercise session in younger but not in older women. Eur J Appl Physiol., 95(2-3):146-52.
 Van Der Heijden, G.J., Wang, Z.J., Chu, Z., Toffolo, G., Manesso, E., Sauer, P.J., Sunehag, A.L. (2010). Strength exercise improves muscle mass and hepatic insulin sensitivity in obese youth. Med Sci Sports Exerc., 42(11):1973-80.
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