In the past few years, we've heard a lot about the relationship of insulin and blood sugar, but there's a lot more to it. Insulin is a complicated hormone with a lot of effects on the metabolism and circulation.
What Insulin Does
When cells receive the insulin signal, they:
- Take up glucose from the blood for fuel. Liver and muscle cells also make glycogen and store it for later in the day.
- Take up fatty acids from the blood to make triglycerides (glycerine plus 3 fatty acids) for storage
- Take up circulating amino acids from the blood to make more proteins
- Take up potassium from the blood
- Slow down the rate at which they break down proteins
- Slow down the rate at which they convert triglycerides into fatty acids
- Slow down the rate at which they convert protein and fat into sugar
- Relax the arterial wall muscle, increasing blood flow, especially to smaller arteries, keeping blood pressure low.
Source: Wikipedia article on Insulin
Why Insulin is Released
When blood sugar rises, the beta cells that produce and store insulin take it up and use it to produce ATP, every cell's quick-energy source. When the level of ATP is high enough, the beta cells start releasing insulin.
But sugar is not the only source for ATP production. And a high-protein or high-fat meal can cause higher insulin than a high-starch meal can. Without even raising the blood sugar.
When cells encounter a lot of insulin a lot of the time, they start to ignore it. If the situation continues, they become insulin resistant. If the pancreas can manage it, it will release even more insulin. Some of the effects of insulin resistance are:
- High blood sugar after meals, as the cells ignore the signal to take it up from the blood.
- Low blood sugar between meals. The body does not release enough glucose from the previously-stored glycogen to supply the body's energy needs -- this can lead to mental "fogginess"
- Higher levels of triglycerides in the blood
- High blood pressure.
- An increase in fat storage around the abdominal organs.
Source: Insulin Resistance at Wikipedia