The Glycemic Index rates carbohydrates as having either a high, low or medium glycemic index. And the idea is to eat more foods that have either a low or medium glycemic index, and less with a high one. Low glycemic index foods enter the bloodstream more slowly, and so don't raise blood sugar levels like high glycemic index foods.
So, what is a carbohydrate? All sugars, or foods that are broken down into sugar, are carbohydrates. This includes regular sugar, glucose (often used in sports drinks), fructose, (in fruit), lactose, (found in milk and similar products like yoghurt), maltose, (found in malt which is often used to flavor cereals), all types of starches, from potatoes to noodles and pasta, and legumes, such as lentils and peas (though these also contain some protein).
Fruit is considered to have a low GI (not fruit juice though). Interestingly though, recent research has found what they believe is a link between fructose and obesity. However, the type of fructose studied was in corn syrup, which is a refined and concentrated form of fructose. It also doesn't have the beneficial fiber, antioxidants and other phytochemicals that fruit does. This was also preliminary research done in an animal model, so it may not be valid for humans. Researchers from the University of Florida found that fructose may make people believe they are hungrier than they should be. And when these researchers interrupted the way fructose was metabolized, the rats they were working with did not put on weight, even though they still ate fructose.
This is not the first research that has suggested fructose may be linked to a propensity to put on weight, more so than other types of food. A study at the University of Cincinnati found that eating fructose (high fructose corn syrup), led to greater fat storage. They say that the body processes fructose differently to other types of sugars, though again, it is not clear if this is mitigated by perhaps the lower concentration of fructose in fruit as compared to the corn syrup used in the study.
The research from the University of Florida found that there were higher levels of uric acid in the bloodstream after eating or drinking fructose. This spike in uric acid affects insulin, by blocking it. Insulin regulates the way our cells store and use fat. If uric acid levels are elevated a lot, then symptoms of metabolic syndrome can develop. These symptoms include high blood pressure, high cholesterol levels, as well as gaining a lot of weight. What is of possible concern to people is that fructose is used in a lot of soda drinks, so if you drink a lot of soda it is going to be quite easy to frequently spike uric acid levels in the blood. Metabolic syndrome is also a precursor of type 2 diabetes.
Signs of metabolic syndrome include fat on the abdomen, such that the waist appears as big as the hips or larger. There tend to be lower amounts of the good type of cholesterol in the blood, and high levels of triglycerides which make the blood 'sticky'. Metabolic syndrome is associated with the way the body responds to insulin, so that there are higher levels of glucose in the blood. All of these things can be tested by doctors.
References:
1. http://www.nutraingredients.com/news/ng.asp?n=64395&m=1NIED08&c=qgtqmovbyiaxdub
2. Australian Healthy Food, November 2005
3. Nature and Health, Oct/Nov 2005
