Everyone has experienced a sugar high and low, right? After eating a big piece of chocolate cake, you feel great, but in about 30 minutes, suddenly you get tired. This is because blood sugar (glucose) surges up just after eating the sweet, and you get a large amount of an energy source in the blood. However, the large quantity of the sugar stimulates the brain to send a signal to the pancreas to create tons of insulin and the insulin converts the blood sugar into glycogen, which is stored in the cells. This creates a sudden drop in the blood sugar level. That is why you feel tired.
This does not happen if you eat a complex carbohydrate food such as a whole grain or vegetables, because the complex carbohydrate is slowly converted into glucose in the body and so the impact of the blood sugar surge is kept to a minimum. That is why many health experts recommend eating complex carbohydrate foods (though some of them think we should avoid carbohydrates as much as we can).
There is more. Sugary food makes you really hungry afterward. According to a study done at the Obesity Prevention Center in Boston, if you eat food with a lot of sugar, you will feel hungrier a few hours later.
In their study, researchers gave two different types of milk shakes to the same person; a high or a low glycemic index (an index which indicates how quickly the blood sugar level rises) milk shakes. When the person drank the high glycemic index milk shake, she felt hungrier and ate far more food at dinner time than when she drank the low glycemic index milk shake.
This agrees with a previous study done at the University of Copenhagen. It is well known that people who lost weight through dieting gain back most of their weight after stopping the diet. The Copenhagen study found that, if they limit high glycemic index food after stopping the diet, these dieters can maintain their healthy body weight level.
So, if you are doing a reduced calorie diet to lose weight, especially with a low carb diet, make sure that you won’t put back sugary foods into your diet, after finishing the diet to lose weight. If you would like to know which foods have a low glycemic index, go to
Now, some people may point out that even among sugars, there are several different types and their glycemic indexes are different. This is true, so see the table below.
Sucrose is the standard table sugar, and fructose is the sugar found mainly in fruit and vegetables. Glucose is also found in fruit and vegetables, but it is also known as the blood sugar. All carbohydrates are converted into glucose once they are digested in our body. Lactose is the sugar in milk, which some people cannot digest. Honey is not a type of sugar, but many people use it to sweeten things. Since its (averaged) glycemic index sits at the borderline between high/low glycemic indexes; I have listed it there.
Seeing this, many people may wonder why we are hearing the news saying that fructose is a bad sugar. It has the lowest glycemic index, and it seems good for the body. We often hear that sugar used in soft drinks is fructose extracted from corn and it is really bad for the body, but everyone recommends eating fruit, which is full of fructose. Are there different types of fructose?
The answer is no; there is only one type of fructose. The problem is a quantity. Yes, fruit contains fructose, but a small amount and, if only a small amount of fructose is in the blood stream, it helps the body to process glucose properly. However, most fructose sweetened drinks contain HUGE amounts of fructose, which our body cannot handle.
So what is bad about fructose? Unlike glucose, fructose is processed in the liver. If there is too much fructose, the liver cannot convert it into glucose and starts converting it into a fat called triglycerides and releases it into the blood stream. The triglycerides are a risk factor of the heart disease. In fact, many doctors rely on the amount of triglycerides in the blood when they assess the risk of the heart problems of their patients.
Furthermore, high level of fructose prevents appetite regulating hormones to be secreted, and keeps you hungry — and thus causes weight gain. It is also suggested that it causes insulin resistance.
So if you like to taste sweet things, you may want to eat fruit. Of course even among fruit, the amount of fructose is quite different. For example, a typical apple has a glycemic index of 38, but watermelon has 72!
How Carbs Can Trigger Food Cravings, NYT, Jun. 27, 2013
Effects of dietary glycemic index on brain regions related to reward and craving in men, American Society for Nutrition, Jun, 2013.
Diets with high or low protein content and glycemic index for weight-loss maintenance. New England J. Med. Nov, 2010.
Glycemic index and glycemic load for 100+ foods’ Harvard Medical School Web Site
- Back to Articles