The Glycemic Effect

Glycemia is the presence of glucose in the blood and the glycemic effect describes what happens to our blood glucose levels when we eat. (You'll also see the spellings glycaemia and glycaemic, but they look a little archaic if encountered outside a medical journal. So we're sticking with e rather than ae on this site).

 

 

 

Glucose, C6H12O6 is the primary fuel for all life forms. Whether animal, vegetable or bacteria, all living things use glucose to transport energy around their bodies. Plants pack the energy of sunlight into glucose molecules which they photo-synthesise from water and carbon dioxide. Then, by chaining glucose molecules together they make energy stores in the form of more complex sugars and starches. This results in the food group we know as carbohydrates that are all essentially comprised of glucose building blocks.

 

 

 

Just like plants, we use glucose dissolved in our blood to transport energy around our bodies, in particular to power our brain. When we are not eating, our blood glucose level is remarkably constant, a bit like body temperature. The pancreas is the organ which regulates blood glucose, secreting the hormone insulin if the level is too high, which sends excess glucose to the liver where it is stored as glycogen. If the glucose level is too low the pancreas releases the hormone glucagon which has the opposite effect and converts glycogen back into glucose. Diabetes results when this system isn't working properly [There's an excellent howstuffworks site for more details]

 

 

 

When we eat fats or protein there is very little effect on the blood glucose level. But when we eat carbohydrates there is a very different response. The figure shows the glycemic effect on a normal healthy individual of eating 50g of glucose. (This is by definition a glycemic load of 50g). The dotted line shows the steady fasting level (in this case about 5.4 mmol/L). Eating this load of pure glucose (about equal to a Mars bar and a large Coke), gives a pretty hefty kick to the system. The glucose you eat rapidly ends up in the blood stream almost doubling the normal level. This secrets a large dose of insulin which starts removing glucose from the blood stream and storing it as glycogen in the liver for future use. In nearly all individuals the fall in glucose is as fast as its rise with the result that it ends up below its normal level.The normal body response to this condition is to send out all the signals saying "eat". So most people do, and if they grab a typical sugary snack, the whole process will be repeated.

So the very act of eating high glycemic food is to trigger the desire to eat more. Many nutritionists are now coming round to the view that continually eating in this high glycemic manner is a major cause of not only obesity but its associated diseases of diabetes and heart failure. For further reading on this there is a good review, with lots of references, on the Linus Pauling Institute website.