Some people load them. Others unload them. According to mainstream science, they're what we burn when we go for a burn, and we couldn't sing dance or, well, breath without them. However, a more radical school of nutrition claims that carbohydrates - especially the simple, refined kind - are the real cause of America's obesity epidemics, and that, unlike protein and fat, they aren't even essential nutrients. American Council on Exercise polled some experts to referee this nutritional skirmish and answer the question: Is there life after carbs?
What are Carbohydrates and What is Their Function?
A carbohydrate is a six-carbon molecule that can shape-shift into many formations. The difference in its chemical structure affects the kind of carb it is, the rate of its absorption by the body and its effect on blood sugar.
The mainstream scientific consensus is that carbohydrates are the body's go-to fuel, our primary energy source, especially for the brain. They also help constitute cellular substances such as nucleic acids, cell walls and cell membranes.
More importantly, they're our sole source of fiber, which is essential in the maintenance of our colon and gastrointestinal tract and the prevention of colon and other cancers.
Simple and Complex Carbs
The two basic varieties of carbohydrates are simple (sugars) and complex. Simple carbs come in two varieties: monosaccharides and disaccharides. The two main monosaccharides are glucose, found in fruit, sugar and honey, and obtainable from complex carbs via process known as hydrolysis; and fructose, found in fruit, fruit juice, honey and engineered foods such as high-fructose corn oil. (In a recent experiment at the University of California, Davis, rats fed a high-fructose diet became abundantly fat, which suggests that we should limit our intake of that sugar.)
The disaccharides are sucrose, maltose and lactose. Sucrose (table sugar), the most important disaccharide, is found in all photosynthetic plants, where it serves as an easily transported energy source. Maltose, which is formed when a malt enzyme interacts with starch, is found in beer and cereals. And lactose is found in milk, whether human or bovine.
The main complex carbs, also known as polysaccharides, are starches, glycogen and fibers. Starch is the reserve carbohydrate in many plants and comprises large percentages of cereals, potatoes, corn and rice. Once in the body, starch is broken down into glucose.
Blood Sugar and Insulin level
The pancreas secretes the hormone insulin when sugar enters the bloodstream; it immediately transports that sugar (glucose) from the blood into the cells. Whatever the cells don't need is stored as fat. Since simple sugars enter the bloodstream quickly, they lead to a very sharp rise in insulin. In turn, these sharp spikes in insulin cause levels of blood glucose, which is being sucked up into the cells, to drop quickly. People are left feeling lethargic and hungry, so they consume more calories than normal. This often triggers "syndrome X" (also called metabolic syndrome), a chain of events made up of overeating, obesity, insulin resistance,type 2 diabetes and heart disease. Because complex carbohydrates are more difficult for the body to metabolize, they have a less severe effect on blood sugar and keep you full longer. They're also nutritionally preferable because they tend to be lower in fat.
How Many Carbs are Too Many?
Here's where things get interesting. Felicia Greer, Ph.D., assistant professor of exercise physiology at California State University, Fresno, represents the traditional wing of nutritional science (as typified by the American Dietetic Association and American Heart Association, among others) She stipulates the following carbohydrate requirements:
Elite athletes - with exception of power lifters and bodybuilders - should get 70 percent of their dietary calories from carbs and at least 60 percent from complex carbs, and ingest simple sugars during their event. "In order to perform on a daily basis," she says, "they need to replenish muscle glycogen stores as quickly as possible." She recommends that they consume fruit or a sports drink within the first 30 minutes following an event to get blood glucose back into the muscles. From 30 minutes to two hours afterward, they should eat a complex carbohydrate (such as whole-grain cereal), and two hours after an event a meal high in carbs that also contains protein and fat.
Strength-training athletes such as power lifters, as well as recreational athletes who work out four to five times a week for 30 to 45 minutes, should get from 55 percent to 60 percent of their diet from carbohydrates.
The deconditioned should get 50 percent to 55 percent of their daily calories from carbohydrates.
As for fiber, everyone needs 25 to 35 grams a day, according to Douglas Kalman, director of nutrition at Miami Research Association, as well as the National Cancer Institute. (The average American consumes just 16 grams).
Most nutrition texts state that the average person should consume 1 to 1.5 grams of carbohydrates for every kilogram of body weight. Not Joey Antonio, Ph.D., who the high priests of carbophilia might call a heretic. Antonio, co-editor of the textbook Sports Supplements, claims that high-glycemic carbs (simple sugars) can increase the risk of cardiovascular disease and diabetes, and that unless one is an ultra-endurance athlete, there's no reason to get from 50 percent to 60 percent of one's diet from carbs. While both of these ideas are gaining more of scientific credence, Antonio goes further. "Strictly speaking," he says, "carbs aren't needed at all. They're not an essential nutrient, like fatty acids, amino acids and vitamins. If you stop eating them, you won't die or suffer a deficiency of any kind." Antonio cites a recent study of the Inuit people of Nunavut, whose diet consists almost exclusively of protein and fat. There was little evidence to conclude that this extreme restriction of carbohydrates was harmful.
Antonio admits that people who go on low-carb diets "may feel sluggish," and adds two caveats: that a diet totally lacking in fiber may ultimately compromise the colon and GI tract, as well as leave the body with inadequate supplies of essential vitamins and minerals. He concludes that carb-lessness is most suitable for the completely sedentary.
For active people, from elite athletes to weekend warriors, Antonio recommends a diet composed of equal thirds lean protein, saturated fat and high fiber carbs. How many grams of carbohydrates can the body process at one time? "Nobody knows", says Antonio, although he notes that ultra-endurance athletes such as Tour de France cyclists consume 10 to 12 grams per kilogram of body weight, or 700 grams of carbohydrates a day.
Do you Need More Carbs on the Day you Work Out?
Again, there are two schools of thought. Greer claims that carbs are most needed in the morning (because half of your liver's glycogen stores are burned overnight), and in anticipation of any athletic activity. "Eat for what you're going to do rather than what you have just finished," Greer advises. Antonio, a proponent of a recent dietary development known as "nutrient timing", suggests the opposite - that the most important time to eat is after your workout, when you should consume a drink composed of two parts of protein to one part of carbohydrate (such as protein powder blended with fruit juice), followed by a full meal an hour or so later.
Are Low-carb Diets Healthy?
No one knows the long-term effects of any diet - most dietary studies last eight to twelve weeks, with the longest six months to a year. However, some new studies demonstrate that a healthy low-carb diet - that is, one such as the South Beach Diet that emphasizes complex carbs and unsaturated fat - can not only help reduce weight, but benefit overall health. For example, a study at the Human Performance Laboratory of the Department of Kinesiology of the University of Connecticut demonstrated that a low-carb diet increased levels of HDL (the "good" cholesterol), while lowering triglycerides.
Source: Fitness Matters magazine, published by the American Council on Exercise
