The U.S. Department of Agriculture’s 2005 Dietary Guidelines for Americans recommends regular exercise (one hour most days) and reduced calorie intake for safe, effective weight loss. The guidelines advise allotting total daily calories as follows: 45%-65% carbohydrates, 10%-35% protein and 20%-35% fat.
The guidelines also point out that the carbs representing nearly half to two-thirds of the diet should consist of “fiber-rich fruits, vegetables, and whole grains,” and that people should “choose and prepare foods and beverages with little added sugars or caloric sweeteners.”
A recent survey by the NPD Group, a market research firm based in Port Washington, NY, suggests the popularity of low-carb diets is waning. During 2004, the percentage of Americans following low-carb diets (e.g., Atkins) dropped from 9% in January to 4% in November.
Carbohydrate myths: In their heyday, low-carb diets claimed to be the key to quick, easy and healthy weight loss. But, there is little scientific proof for these claims. Proponents argue that carbohydrates raise blood sugar (glycemic index), causing excess insulin (hormone that regulates blood sugar) production and insulin resistance and leading to obesity (fat storage), hunger (rapid fall in blood sugar) and cravings for more carbohydrates.
But, this premise is false. The opposite is true. Carbohydrates and protein stimulate insulin release to keep blood sugar levels stable and in normal range. Carbohydrates are not automatically turned into fat unless excess calories are consumed (from carbohydrates, protein or fat).
A calorie is a calorie. Fat provides more than twice as many calories (per gram) as carbohydrates or protein do. Excess calories lead to weight gain which causes insulin resistance and high insulin production. High insulin levels may suppress, not increase, hunger. Complex carbohydrates like beans and whole grains don’t stimulate hunger or cause cravings for more carbohydrates.
Low-carb diets work short-term because they are low in calories and may also cause water and muscle loss. High-protein, fatty foods like meat are filling but can become monotonous over time, so fewer calories are consumed.
In numerous scientific studies, diets high in fat and low in fruits, vegetables and whole grains increased risk of chronic diseases. But, foods rich in fiber and complex carbohydrates (starch) like pasta, bread and potatoes helped people lose weight, since they are satisfying and low in calories. Fiber also slows absorption of sugar (preventing blood sugar spikes and excess insulin response) which reduces hunger.
The brain can’t function without carbohydrates. Low-carb diets may provide only 20 to 100 grams of carbohydrates daily. The Institute of Medicine (IOM) advises at least 130 grams of carbohydrate daily—mainly from whole grains, fruits, vegetables, beans and lowfat dairy products (contain lactose). Quality and quantity of carbohydrates are equally important for health.
Glycemic index: Some low-carb diets (e.g., South Beach, The Zone, Atkins, Sugar Busters) recommend eating foods with a low glycemic index (GI) and avoiding foods with a high glycemic index. The GI categorizes foods (50-gram-carbohydrate portions) by how high they raise blood sugar compared to a standard like white bread or sugar. High GI foods include carrots, raisins, white rice, potatoes, watermelon and cereals. Examples of low GI foods (high in fiber) are beans, unrefined grains, some fruits and non-starchy vegetables.
The GI is not practical, since it’s based on eating foods alone, not as part of a meal. The GI and glycemic load (based on actual portions) are not effective tools for planning menus or predicting the amount of insulin release, weight loss or health benefits.
Many variables can affect GI including food processing, ripeness, preparation (e.g. mashing, cooking), portion size, physical activity, health status, body weight, other foods eaten at the same time, other nutrients in the food, and blood sugar before eating.
Low-carb diets (high in protein and fat) may lead to the following health problems:
Comparing diets: Several research studies have compared weight loss from low-carb diets like The Atkins Diet to low-fat diets. After six months, overweight subjects lost more weight with low-carb diets and, consequently, had lower blood sugar, cholesterol and triglycerides (risk factors for heart disease) and higher “good” HDL-cholesterol (protects against heart disease).
But, after one year all dieters lost about the same amount of weight (5% on average) and had similar improvement in cardiac risk factors (probably due to weight loss). Larger, long-term studies are currently underway.