Thursday, December 8, 2011

Glycemic Index

Okay, so you're eating enough food, and you’re going high-fiber, so it's easy to fill up with relatively little in the way of calories. But there is a third point you need to know about, particularly if you've been battling a weight problem. Within the world of high-fiber foods, some do a better job of keeping your blood sugar steady than others. Let's go back to our breakfast table for a minute and compare a bowl of oatmeal, on the one hand, with a wheat cereal on the other. Yes, they're both better than bacon and eggs - by a long shot. And they both have about the same amount of fiber. But these two cereals have different effects on your body, as researchers have demonstrated. In one four-week study, researchers gave men whole wheat cereal (Weetabix) for breakfast, along with whole wheat bread. Then, for another four weeks, they switched to a muesli made of oats, apple, and a bit of fruit sugar (fructose), along with pumpernickel bread. 

The researchers then checked the men's blood sugars and there was a surprisingly big difference between the two breakfasts. The oat based breakfast stabilized blood sugar much more effectively than did the wheat-based breakfast. And a more stable blood sugar means that your appetite stays under control. Now, wheat or corn cereals taste great and have no cholesterol and little fat. You really cannot fault them. But they don't have oats' power to stabilize blood sugars, and that's what counts when it comes to keeping your hunger in check.

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Scientists rate how quickly foods release their natural sugars into the bloodstream using a number called the glycemic index, or GI. Foods with a low glycemic index release their natural sugars slowly over a long period of time. That's handy; it means that hunger will not return too soon. When you eat a typical low-GI food, it acts as a constant source of energy, providing you natural sugars, minute by minute, on an ongoing basis. It will not let your blood sugar climb too high, and if your blood sugar doesn't zoom up to a peak it will not be able to crash. High-GI foods are just the opposite. They release their sugars quickly, prompting a return of appetite and more snacking later in the day. One caveat: The GI value of foods is a matter of continuing scientific study, and it clearly matters more for some people than others. If you have been slim all your life and have no trouble with your weight, GI values are not especially important for you. Almost certainly, your body handles sugars very efficiently and never lets your blood sugar get too far out of line. You'll want to pay more attention to fiber content. If, on the other hand, you've struggled with your weight for some time, those added pounds have probably made your blood sugar harder to control, because extra weight makes your body tissues more resistant to insulin, the hormone that controls your blood sugar. This is especially true if diabetes runs in your family. You'll want to be sure to go high-fiber and low-GI with the foods you eat. Among low-GI foods, beans again win out and green vegetables score very well, too. Most fruits have low GIs, but there are a few notable exceptions, as we'll see. Grains vary dramatically—some are low, others are high, and we'll soon learn which are which. Candy, honey, and white bread are examples of high-GI foods. 

What is it about some foods that make them release sugars slowly and steadily, while others send sugar into your bloodstream almost explosively? If you could examine any carbohydrate-rich food—a bean, a carrot, or a bit of pasta, for example—under a powerful microscope, you would find that, for some, the carbohydrate molecules are long and straight, and are stacked up in an orderly way, like a dense pile of wood. When you eat them, it takes time for digestive enzymes to break up these densely packed molecules. These slow-digesting foods will not perturb your blood sugar very much. Beans, peas, and lentils are in this low-GI category. Many types of rice are, too. In this case, fiber is not the issue. It all has to do with the arrangement of the carbohydrate molecules. On the other hand, high-GI starches are built from molecules that are branched, like piles of small twigs. Enzymes quickly break them apart, releasing all their sugars into the blood at more or less the same time. Typical wheat breads—even whole wheat bread—are in this quick release category, as are bagels. In contrast, rye and pumpernickel release their sugars much more slowly. Again, it's not fiber that does the trick. It is a question of how the carbohydrate molecules are aligned. So, to keep your blood sugar steady, don't avoid breads. Just be selective about which ones you choose. The same is true for potatoes. Baking potatoes have a high GI and release their sugars quickly, while sweet potatoes and yams have much lower GI values.

Triglycerides: Fatty Acids and Glycerol

Very few fatty acids are found free in the body or in foods; most are incorporated into large, complex compounds: triglycerides. The name almost explains itself: three fatty acids (tri) arc attached to a molecule of glycerol to form a triglyceride molecule. Tissues all over the body can easily assemble triglycerides or disassemble them as needed. Fatty acids can differ from one another in two ways: in chain length and in degree of saturation. Triglycerides usually include mixtures of various fatty acids. Depending on which fatty acids are incorporated into a triglyceride, the resulting fat will be soft or hard. Triglycerides containing mostly the shorter chain fatty acids or the more unsaturated ones are softer and melt more readily at lower temperatures. Each species of animal (including people) makes its own characteristic kinds of triglycerides, a function governed by genetics. Fats in the diet, though, can affect the types of triglycerides made because dietary fatty acids are often incorporated into triglycerides in the body. For example, many animals raised for food can be fed diets containing softer or harder triglycerides to give the animals softer or harder fat, whichever consumers demand.

Diabetes in History

Writings from the earliest civilizations in Asia Minor, China, Egypt, and India have documented the problems with diabetes mellitus, referring to patients with boils, infections, excessive thirst, loss of weight, and passing copious amounts of honeysweet urine, which often drew ants and flies. The term diabetes is derived from the Greek work meaning "siphon," or the passing through of water, and mellitus comes from the Latin word for "honeysweet." The Papyrus Ebers, an Egyptian paper dated about 1550 B.C., recommended that those afflicted with the disease go on a diet of beer, fruits, grains, and honey, which was said to stifle the excessive urination. Indian writings from the period attributed diabetes to overindulgence in food and drink. In northern European countries during the 15th, 16th, and 17th centuries, meals consisted primarily of roasted meats dripping in fat, sugary pastries, and plenty of butter and cream, but only small amounts of whole-grain breads or green, leafy vegetables. "It is, therefore, not surprising that many cases of diabetes were reported during these times of abundance. It is noteworthy, too, that during this period doctors had to taste the urine of patients for sweetness in order to detect the disease."5 Eventually, doctors centered on two schools of thought concerning diet. One school suggested dietary replacement of the sugar lost in the urine, while the other camp believed in restriction of carbohydrates in order to reduce the effects attributed to an excess of sugar. The first school was exemplified by Thomas Willis, a British physician who, in 1675, recommended a diet limited to milk, barley water, and bread. The diet was high in carbohydrates but low in calories. The other school was promoted by Dr. Rollo, a British military surgeon who, in 1797, began the trend toward high-fat, high-protein, and low-carbohydrate diets by prescribing mainly meat and fat. Some of the patients apparently were helped by the diets, as evidenced by reductions in the amounts of sugar spilled in the urine. Caloric restriction appears to have been the most effective therapy, since a French physician named Bouchardat found that the limited availability of food in Paris during the Franco-Prussian War of 1870-1871 brought marked reductions in the sugar spilled by his diabetic patients.

A major breakthrough in understanding the pathology of diabetes came in the latter part of the 19th century when Paul Langerhans, a German pathologist, while examining a pancreas under a microscope, discovered tiny cells that were different from the rest of the pancreatic tissue; these were later named the islets of Langerhans. Many physicians attempted to cure diabetes with extracts of the pancreatic islets, but these attempts were unsuccessful. This was because the extracts were contaminated with digestive juices from the pancreas that destroyed the activity of insulin, which is a protein.

In 1921, Frederick G. Banting and Charles H. Best, working at the University of Toronto, in Canada, discovered that they could obtain biologically active insulin from dogs and that the insulin cured the diabetes in dogs who had had their pancreases removed. The insulin was later given to a male diabetic human, who experienced a remarkable recovery. The use of insulin brought a dramatic drop in deaths due to diabetic coma and greatly increased the years of survival following detection of the disease. However, the insulin initially used brought sharp drops in blood sugar levels (hypoglycemia), which resulted in distressing symptoms. New forms of the hormone were developed by chemically modifying the substance so as to slow its action. One modification was developed in 1936 by a Danish researcher named Hagedorn, who added protamine, a protein-like substance. This and other modifications of insulin made it possible to use only one daily injection, instead of the three or four originally required.