Organizations recommend that carbohydrates should make up the majority of calories (between 55% and 60%), fat should not exceed 30%, and protein should be kept at 10% to 15%. Many popular diet books, however, challenge the traditional diet. The Atkins diet, Zone diet, Protein Power and other alternative dietary approaches, all reduce carbohydrate intake, as we have discussed in the entry on low carbohydrate diets. They advocate for increased intake of fat and/or proteins.
Low Carb Diet
The low-carb diet is believed to aid in weight loss and provide a number of other health benefits by reducing insulin production. The low glycemic (low-GI), diet is a compromise between low-carb and high-fat diets. It retains the low-carb diet’s focus on insulin but suggests differentiating certain carbohydrates over others. When the evidence is reviewed, it becomes clear that not all carbohydrates are created equal.
Pure glucose, for example, is absorbed quickly and causes a strong rise in blood sugar and insulin. Some, such as pure glucose, are absorbed slowly and produce a small blood sugar and insulin response. Low-GI diet advocates claim that eating foods from this category will increase weight loss and improve your health. As we will see, there is no evidence that low-GI diets increase weight loss.
Glycemic index is a measure of the food’s glucose-stimulating effects. A food with a lower effect on increasing blood sugar (and insulin) is assigned a lower glycemic score. The glycemic indice of glucose is arbitrarily set to 100. These ratings are given to other foods in the following manner: Researchers first calculate a portion size for each food item to provide 50 g. Next they give the food to at most eight to ten people to measure their blood sugar response.
Researchers may also give each participant equal amounts of glucose and take the same measurements. The two results are then compared to determine the glycemic index for a food. If a food causes half the blood sugar rise, it gets a GI 50. If it causes 25%, it gets a GI 25. The lower the Glycemic index is, the better. There have been some surprises in the determination of Glycemic index.
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Baked potatoes received a reading of 93. This rating is higher that almost all other foods, including sweet potatoes (54), ice cream (61), and white bread (71). Low-GI diets recommend that potatoes be avoided. However, potatoes are not a concern. Below is a discussion on glycemic loads. Although a food must be tested to determine its glycemic index, there are some guidelines that can be used.
Fiber content is thought to lower the glycemic score of a food by slowing down digestion. Whole grains have a lower GI score that refined or processed grains. The GI score is also reduced by fat content. Simple carbohydrates, such as sugar, often have a higher GI score that complex carbohydrates (such brown rice). There are many exceptions to these rules. The GI measurement can be affected by factors such as the acidity of food, the size of food particles, and the exact mixture of fats and proteins. A measurement such as the glycemic indicator must be reproducible across subjects in order to be meaningful. This means that a potato with a glycemic score of 80 should be comparable to a potato with a similar glycemic score when given to another person. This test passes the GI. Individual foods have a glycemic index that is relatively constant across people.
The GI of a food does indeed indicate its propensity for increasing insulin levels. It is not clear if a diet based upon the index will help with weight loss. It is easy to follow a low-glycemic index diet. You follow the American Dietetic Association’s recommended diet, but you choose carbohydrates at the lower end on the glycemic index scale.
The Glucose Revolution and other books provide a lot of information about how to make these choices. But do low glycemic index diets help with weight loss? This theory may have some problems. Low-GI diets can help you lose weight. There are two main reasons why. Insulin levels are the most important reason.
These books basically show that low-GI diets decrease insulin release. This then makes it almost obvious that weight loss should be possible with lower insulin levels. The second part of this assertion is not supported by any evidence. While excess weight can lead to elevated insulin levels, there is little evidence to support the opposite.
However, reducing insulin levels can help reduce excess weight. Low-GI books are another reason to follow this diet. They claim that low-GI foods are more filling than high-GI foods and keep you fuller for longer. We will see that there is more evidence in support of this belief than against it. The Satiety Index is a measurement that assigns a numerical value to the food’s filling quality.
These numbers are calculated by feeding people fixed amounts of food, then determining how hungry they become again and how much they eat at each meal. This process is similar to how the GI index was established. These measurements don’t support the low-GI diet advocates. It turns out that foods with the highest GI index (or the lowest) are often the most satiating.
This is exactly what low-GI theory advocates would have you believe. The Satiety Index, which measures the satiating power of potatoes, is a good example. As mentioned, potatoes received a poor rating in the GI analysis. According to low-GI theory, you should feel hunger pangs within a few hours of eating a large baked potato. This is not the case in real life.
There are other contradictions between research findings, and the low-GI/high satiety theory. One study found no difference between fructose (fruit sugar), and glucose when it was taken as part of a mixed dinner. This despite fructose having a GI that is more than four times higher than glucose. The satiety argument for low GI diets doesn’t seem to be supported by the facts. Is the glycemic indicator the correct measurement? Is it the wrong way of assessing the insulin-related effects on food? This is based on evidence. Instead of judging from the GI, a more sensible approach would be to measure the glycemic load, which measures the true effect of the food.