Our bodies like a certain amount of glucose in the blood stream at any one time. If it gets too high then the body will release a hormone called Insulin. If the glucose levels get too low then the body will convert glycogen (stored in the liver) into glucose to raise the blood sugar level.
Lets look at the process of Insulin first. So you have been eyeing up the donut sitting on the end of your desk and finally given into temptation. The sugar and carbohydrates in the donut are converted really quickly (because they have a high GI) and we get a spike in our blood sugars – over the body’s comfort level. Insulin is then released to combat this spike and bring the blood levels back down. Insulin reacts with receptors on the cells (remember insulin is a hormone and hormones are just messengers – like a carrier pigeon letting the cells know what is going on in the body). The cell gets the message that there is alot of glucose and it opens up to take in the fuel. This happens to all cells so they have fuel to live but importantly for this post it happens to muscle cells and fat cells. This is great for the muscles giving us energy to be active but not so good for the fat cells – causing the fat cells to store it as fat!
Insulin also has a big impact on the liver. The liver is the biggest internal organ, it works 24/7/365, has hundreds of jobs and is essential to life. Among its jobs it is used as a storage room, it stores reserves of glycogen, iron, copper and vitamins A, D, E and B12. The message that the liver gets from insulin is to absorb glucose from the blood and the liver then converts this to glycogen and stores it for later use.
So the donut has been fully digested, blood sugar levels shot up, insulin came to the rescue and now the blood sugar level is at a comfortable level…. unfortunately because it was a quick and rapid rise in blood sugar, too much insulin was produced meaning we now have the opposite problem and blood sugar is too low (have you ever had a sugar crash? Feel great, lots of energy, buzzing, then all of a sudden…. drowsy … tired ….. feel rubbish….). At this point, insulin’s alter ego comes into play. The pancreas detects the blood sugar levels are too low and it releases a hormone called glucagon. ( Don’t get confused – glucose, glycogen and glucagon. Glucose – blood sugar, glycogen – stored form of glucose & glucagon – hormone to increase blood sugar). Insulin acts on the whole body telling every cell in the body to absorb glucose but glucagon only acts on the liver telling it to convert glycogen back into glucose and therefore increasing the blood sugar levels. Blood sugar levels will naturally drop over time if you haven’t eaten for a while, causing a release in glucagon so you do not need any insulin for this to happen. The more this happens the harder the liver has to work and can cause problems.
As I said above, insulin will act on both fat and muscle cells. We can however manipulate it to work in our favour. We can make our muscle cells insulin sensitive so our muscles will absorb the glucose before the fat cells get the chance. Some studies have even shown that people with type 2 diabetes (where the body has built up a resistance to insulin) can make their muscle cells insulin sensitive enough that for a short period they would no longer be classed as diabetic. How do we do this? Exercise! After exercise the muscle cells become insulin sensitive for a short period and are like a chick in the nest, waiting for mum to come home and grab whatever food they can. If however we have been sat on the sofa for the last few hours, all that insulin is going to go straight towards fat storage.
Carbohydrates (pasta, rice, bread) are converted easily into glucose, Protein and Fats are less likely to cause a significant raise in blood sugar levels. . Some of the best carbs for post workout I have found are sweet potato, rice, oats and bananas. Somebody trying to build muscle would do well with white rice (high GI) where somebody trying to lose “weight” would do well with basmati rice (lower GI).