Low-carb diets have garnered much attention, both positive and negative, since the 1990s. While they reached their peak in the '90s and early 2000s, the misleading idea that "carbs make you fat" still hangs around. The more accurate statement is that "refined carbs and sugar can make you fat." All carbohydrates, simple or complex, break down into blood sugar, or glucose, during digestion and do get stored as fat if you consume more of them than you burn.
How Carbs Work
Glucose is the body's main source of energy. When it enters your bloodstream, your pancreas releases the hormone insulin to help the cells of your body take in and use the glucose. If you do not use all the glucose right away, it becomes glycogen, which is stored in your liver and muscles for later use. When the glycogen stores are full, the excess glucose is stored as fat. Before you can burn fat, you first need to burn the glucose in your bloodstream and the glycogen in your liver.
Whole Vs. Refined
Added sugars and refined carbs, such as soda, white rice and pasta, digest quickly and flood your bloodstream with glucose, provoking a spike in insulin. They are calorie-laden but nutritionally deficient, satisfy your appetite and energy needs only briefly, and may cause you to eat even more carbohydrates. Over-indulgence in refined carbs and sweets begins a cycle of increased blood sugar, increased insulin response, and increased fat storage. The action of insulin causes carbs, protein and fats in excess of immediate energy needs to be deposited for storage as fat. Complex carbs, on the other hand, including whole grains, vegetables, beans and legumes, are full of nutrients and digest more slowly, allowing insulin to maintain a more even level of sugar in your blood. When your carbs come from whole grains and fiber, you are less likely to store glucose as fat.
The Insulin Response
The glycemic index, or GI, of a carbohydrate is a measure of how quickly it raises your blood sugar. On a scale of 100, simple carbs, sugars and refined, processed foods have high GI value and provoke a greater insulin response in order to move that large amount of glucose into your cells. The trouble comes when you eat too many and too much of those high GI foods for too long. Your pancreas will continue releasing insulin to lower your blood glucose, but the more insulin there is in your blood, and the longer it is there, the more resistant your cells become to it, and the more weight you gain. This is insulin resistance. Without action on your part in the form of a healthy diet and exercise, your cells eventually will not be able to take in the glucose. It will remain in your bloodstream and you eventually become diabetic.
Glycemic Load
This is not to say that you can never eat ice cream again. Unlike the glycemic index, glycemic load, or GL, takes into consideration both the GI and the serving size. It is a more specific measure of how much glucose enters your bloodstream. To find a food's GL, multiply the number of carbs per serving by the GI and divide by 100. A number 20 and higher indicates a high GL. Medium is 11 to 19, and low is 10 or less. A 1/2 cup serving of ice cream has a GI of 61 on a scale of 100. Multiply 61 by 13 carbs per serving and divide by 100, and you arrive at a low glycemic load of 7.93. GI and GL tables are available online and in many diet and healthy eating books to help you manage your carb intake.
References
- "Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat..."; Food and Nutrition Board; 2005
- National Digestive Diseases Information Clearinghouse: Your Digestive System and How It Works
- U.S. Department of Health and Human Services: National Diabetes Information Clearinghouse -- Insulin...
- Massachusetts Institute of Technology; Glycemic Index; March 2006
- Harvard School of Public Health: The Nutrition Source -- Carbohydrates and the Glycemic Load
- Oregon State University; Linus Pauling Institute; Glycemic Index and Glycemic Load; Jane Higdon; 2010
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