What is a Glycemic Index (GI) and what does it mean you may ask. The glycemic index, is a system to measure how quickly or how slowly a food causes your bodies blood glucose level to rise. Pure glucose (sugar) scores 100 on the GI. It's pure sugar and of course, makes your blood sugar raise up the fastest. On the other end of the spectrum you have stuff like chickpeas (hummus) which only score a six on the G.I. because they cause your blood sugar level to raise very slowly. If You're an endurance athlete then you may want foods with a high GI, because your body has to supply energy to your muscles. If you're trying to lose weight, are diabetic, or someone that doesn't get much exercise like most of us truckers, then you may want to stay away from foods with a high GI.
There's more to staying healthy than just eating foods with a low glycemic index though. According to a Harvard Health Publications article, there are foods that have a very high GI Like Watermelon, which score an eighty, or the lowly peanut, which scores a 50; yet, don't cause your blood glucose level to rise much at all. This is because they posses very little carbohydrate per serving.
In order to make good food choices, You need to know how quick the glucose enters the bloodstream, and how MUCH glucose (carbohydrate) it has in total per serving. These two factors together, are called the glycemic load. You find the glycemic load "by multiplying the grams of a carbohydrate per serving, by the glycemic index, (GI) then dividing by 100. A GL of ten or below, is considered low. Twenty or above, is considered high."
That Lowly peanut that scored a sky high fifty on the GI, on the GL only scores a one and a cashew only scores a three! So, by all means driver. Instead of chowing down on something like say... raisins, which have a GL of 28. Keep your blood sugar low, and buy a can of mixed nuts, and wash it down with some whole milk, which has a GL of four, or tomato juice with a GL of three, and make it a great healthy, low blood sugar day driver
Here's a link to an awesome article which explains all this much better than I do and which also has a chart that shows the glycemic index AND the glycemic load for 100 different foods. http://www.health.harvard.edu/diseases-and-conditions/glycemic_index_and_glycemic_load_for_100_foods