These terms can get to be a bit confusing. Basically, the Glycemic Index (GI) is based off of the blood sugar response that 50g of carbohydrates from a specific food will give you. The GI is a rating system that gives a food a number on a scale of 0-100 that relates how fast and how high those carbohydrates will spike your blood sugar after consumption.
It is talked about in Diabetes management because it is important to manage blood glucose levels to minimize complications. By avoiding high glycemic foods, diabetics can avoid spikes in blood sugar levels, and also importantly low blood sugar. To a person without Diabetes, it is also important to have steady blood sugar levels because too much can increase insulin production which over time will increase adipose stores, insulin resistant and Type II Diabetes. Too little blood sugar will leave you feeling weak and lethargic.
Consequently, choosing foods that have a lower GI rating are generally healthier. They include whole grains, nuts and seeds, lean proteins and vegetables. Some exceptions include fruits, starchy vegetables like beets, and grains such as millet.
The GI of a food can be effected by many factors including how old it is ( very ripe banana has a higher GI than a green one), how it is processed/cooked ( the more it is cooked, generally the higher the GI), its form (mashed vs. diced potatoes), its temperature (hot vs. cold potatoes), how much, and with what it is consumed (bread alone has a higher GI than bread with butter).
The Glycemic Load (GL) is a bit more practical. This term takes the GI number and adjusts it to reflect an amount normally consumed. For example, eating 50g of carbs from pasta is realistic and won’t change the number that much, however eating 50g from watermelon would be quite a feat, so the number will most likely drop.
The GL can be manipulated in a number of ways by altering the variables mentioned above. For example, if there is a food with a higher GI you can lower its GL by combining it with a fat or protein to slow digestion and glucose metabolism. For example, have a piece of fruit with some nuts or seeds, or eat beets with a fillet of fish for dinner. If you are craving something sweet, you can substitute regular sugar with a less processed form such as Sucanat, which has a lower GI and bake with whole instead of light grains to lower the GI.