Carbohydrates themselves aren't necessarily a bad thing, being a major staple in the diet. However, there can be problems associated with eating too many of them. Many people believe that weight gain is mainly due to eating too many carbohydrates. In fact, people gain weight because they eat too many calories, which is not the same thing: calories come from carbohydrates (4 calories per gram), proteins (4 calories per gram) and fats (9 calories per gram).
Further complicating the situation is that it's not only the amount of carbohydrates you eat, it's also the type that's important. For example, when we eat a baked potato, we get a more rapid spike in blood sugar than we do even after eating pure sugar.
Some suggest that eating too many carbs that are refined or in the form of sugar can make it difficult to control weight because they are so quickly absorbed, sending blood sugar levels soaring, followed by high surges of insulin. After two or three hours, the large amounts of insulin bring the blood sugar levels crashing down, sometimes even below normal levels. At this point, people feel strong urges to look for snacks well before the next meal. Over many years, these powerful surges of insulin exhaust the pancreas to the point where diabetes can develop.
Most people consume too many refined carbohydrates such as white bread; whole grains not only create lower blood sugar and insulin spikes, but contain far more vitamins and minerals as well.
The Glycemic Index
The glycemic index of a food is a measure of the relative speed at which carbohydrates from it enter the blood stream. Scientists measure that speed and compare it to how quickly after ingestion 50gm of glucose appears as blood glucose. The glycemic index for glucose is 100. The glycemic value for other foods tells you how close that food comes to glucose in terms of the rate of glucose availability from that food's carbohydrates; the higher the number, the faster the carbohydrates appear in the bloodstream.
The glycemic index of a given food depends on a number of factors. In general, fiber, fat and protein slow down the absorption of carbohydrates in foods. The way a food is prepared also affects its glycemic index; for example, mashed potatoes release carbohydrates faster than a baked potato (but only if the portions tested contain the same amount of added fats).
This can be very confusing, and if you consult glycemic index tables, you are likely to become even more confused, because the numbers often go against common sense and against other good nutritional advice. For example, the glycemic index for carrots is 95, while the glycemic index for table sugar is 65. A baked potato is 93, while Frosted Flakes is 55. Selecting foods with a low index is not necessarily the best choice!
Should we really quit eating carrots? Or choose plain sugar instead of a baked potato? Knowing the glycemic index of food actually has very little use, because a food is often eaten with other foods. A baked potato, for example, is often eaten as part of a meal that also contains proteins, fat and fiber. Thus, if you are concerned about preventing a rapid rise in blood sugar, you should really know the glycemic index of the whole meal, but there are no tables for this.
Another reason the glycemic index of a food does not tell the whole story is that the food's effect on your body also depends on the total amount of carbohydrates present in the portion you are consuming. So, for example, while carrots have a very high glycemic index, a normal portion of carrots does not contain a large amount of carbohydrates, so the total glycemic load (a product of glycemic index and the amount of carbohydrates in the portion of food consumed) is not so high.
In addition, while there may be good reason to prevent rapid rises in blood sugar, especially for people with diabetes, simpler advice includes avoiding refined carbohydrates and empty calorie foods, and consuming plenty of fruits, vegetables, legumes and whole grains. Simpler advice also includes limiting calories and portion sizes if weight control is your goal. In short, you can eat a healthy diet without ever having to consult a glycemic index table.
The theory behind eating low glycemic index foods is that, with such foods, blood glucose rises slowly, and less insulin is released in response to this slow rise. Less insulin means a less dramatic fall in blood sugar and, supposedly, less hunger. Less hunger can mean less food consumed which, hopefully, will lead to weight loss.
Any diet that helps you eat fewer calories can help you lose weight. If limiting food choices to those with low glycemic indices causes you to eat less, then you might lose weight. But you would also lose weight by limiting empty calories and keeping an eye on portion sizes.