The Truth About Low-Carb Diets
Do you think low carb diets will help you lose weight? Well, here’s what you need to know before you pass up the potatoes.
These days, we’re skipping the bread basket in record numbers and shunning starchy vegetables. It seems like a new low-carb eating plan bursts on the scene every few months. And nearly one in three adults report that they’re cutting down on or completely avoiding gluten according to market-research firm NPD Group. “Carb-phobia has really taken over people’s minds,” says Kim Larson, RDN, a spokesperson for the Academy of Nutrition and Dietetics, and many St. Louis personal trainers.
But here’s the thing: Eliminating carbs is risky business. “It’s preposterous,” says David Katz, MD, director of the Yale University Prevention Research Center and author of Disease-Proof. “All plants are carbohydrate sources, so eating no carbs means eating no plant foods, period.” Carbs are important for your brain and body; the right ones even reduce your risk of disease.
You can’t live without carbs
While many of us think of carbs as bread and pasta they’re in any food that comes from a plant, including fruits, vegetables, nuts, grains, seeds and legumes. “It’s a huge, diverse class of foods,” Dr. Katz explains. And very frustrating for Brentwood, Mo personal trainers.
To make carbohydrates, plants trap the sun’s energy inside molecules of glucose—a simple sugar—then connect the glucose molecules together (sometimes along with the other two basic sugar building blocks, fructose and galactose) to create longer carb molecules such as sucrose and starch. When you eat that plant, your digestive system breaks the longer carbohydrate back down into glucose, which travels through your bloodstream into your cells. The cells process the glucose, releasing the captured energy and using it for fuel.
Far from being poison, then, glucose sparks life. “If you’re in a hospital and they need to get some energy into you, they’ll use a glucose drip,” says Joanne Slavin, PhD, professor of food science and nutrition at the University of Minnesota and chair of the 2010 Dietary Guidelines Advisory Committee on Carbohydrates. Dr. Katz adds, “If you don’t have enough glucose in your blood, you’re dead. It’s that simple.”
While you don’t have to eat carbs to get glucose into your blood (your body can manufacture it if needed), “carbohydrates are the most efficient fuel source that we have,” says Heidi Schauster, RD, a nutrition therapist in Boston. Low-carb advocates (most famously Robert Atkins, MD) point out that your body can also use other fuel sources, such as protein or fatty acids, to power itself. But many experts say that this method of converting fats into so-called ketone bodies, known as ketogenesis, is much less efficient than using glucose for energy. And when too many ketone bodies are produced, the body is in a state of ketosis. “Ketosis can be tolerated for a short time, but in severe cases it could have very serious effects in the long term for the brain, as well as the kidneys, liver and skeletal system,” Dr. Katz says.
Besides providing much-needed glucose, plants are our only source of dietary fiber. Like other carbohydrates, fiber is composed of many bonded sugar units, but human enzymes can’t chop it up, so it passes relatively unscathed through much of the digestive tract. And it benefits you in many ways. “People who eat more fiber have less cardiovascular disease,” Slavin says. “They also weigh less and gain less weight over time.”
You probably know that fiber helps move food through your body, keeping you regular. In addition, some forms of fiber (including resistant starch, found in bananas, lentils and many other foods) are prebiotics, a type of carbohydrate that feeds the growth of “good” bacteria in your gut.
Not to mention, skipping carbs could mean falling short on essential nutrients. “Cutting out whole grains eliminates a good source of great nutrition, such as zinc, magnesium and B vitamins,” Larson says. Steer clear of fruits and vegetables and you miss out on many vitamins and powerful antioxidants. These nutrients play a critical role in keeping us healthy long-term. “When we look at population-level studies of people who live well across the span of a lifetime,” Dr. Katz notes, “they almost universally eat diets high in good carbohydrates.”
No doubt, you can drop pounds on a low-carb diet in the short run. A 2012 review of studies (most of them lasting 12 months or less) found that obese people on lower-carb diets lost weight and improved their cardiovascular health (lower blood pressure, higher good cholesterol). But when low-carb diets are compared with other plans, the results are less impressive. A landmark Harvard study published in 2009 in The New England Journal of Medicine randomly assigned overweight people to one of four diets with similar calorie counts but different proportions of fats, carbs and proteins to see whether a low-carb diet (getting 35 percent of calories from carbs) had any benefits over diets with higher carb counts. Surprise: After two years, there was little difference in weight loss among the participants; all the diets led to improvement in cardiovascular risk factors as well. In other words, in the short term you’ll likely lose weight on any diet that cuts calories.
The right way to eat
“We know what a healthy diet is,” Dr. Katz says. “All the studies that show better health outcomes over the long term are rich in plant foods—real plant foods, not highly processed, sugar-added, glow-in-the-dark crap.” Think of Mediterranean, DASH and other ways of eating that have been linked to better health, adds Robert H. Eckel, MD, professor of medicine at the University of Colorado Anschutz Medical Campus and former president of the American Heart Association: “Those are not low-carb diets.” Maurie Cofman, C.E.S. personal trainer in St. Louis, Brentwood and Clayton, MO believes in the Mediterranean diet.
So what level should you shoot for? The Dietary Guidelines for Americans recommends that adults consume 45 to 65 percent of total calories from carbs. “Endurance athletes, who burn lots of energy, are at 65 percent, whereas diabetics who are limiting their carbs would be on the 45 percent end,” explains Los Angeles dietitian Lori Zanini, RD, spokesperson for the Academy of Nutrition and Dietetics.
To keep it simple, Larson recommends using food groups to guide your choices; aim for about four servings a day of whole grains (one serving equals 1/2 cup of cup cooked grains or whole-grain pasta, or one slice of whole-grain bread) and five to eight servings a day of fruits and vegetables (1/2 cup of berries, one piece of whole fruit and 1 cup of leafy greens all count as one serving). Limit foods and drinks with added sugars—these are the carbs linked to insulin resistance, heart disease and obesity.
If you’ve sworn off carbs for a while, it can be scary to put them back on your plate. “I tell my clients, ‘Think about adding back in some grain foods for a couple of weeks to see how you feel,'” Schauster says. “Very often, after doing that, they realize, I have so much more energy, I get more out of my workouts, I don’t feel cravings. A lot of things will shift.”
Most of us relish the chance to enjoy juicy fruit and filling starchy veggies again, Larson adds: “When I show people what they can eat, there’s such a sense of relief. They say, ‘Really, I can do that?'”
Should I be eating low-GI foods?
Glycemic index, or GI, refers to how carbohydrates affect blood glucose levels: Low-GI foods tend to raise blood sugar more slowly than high-GI foods. But the measurement doesn’t take into account how much of the food is eaten in a typical serving, which can skew results, Slavin explains. Watermelon has a high glycemic index, for example, but since it’s mostly water, you don’t eat that many carbohydrates in one serving, so it doesn’t actually raise blood sugar significantly.
For people who aren’t diabetic, experts say that GI isn’t all that helpful; instead, focus on adding carb foods that are also rich in fiber, which helps slow digestion and prevent blood sugar spikes.
For more information on low carb diets, contact Maurie Cofman, C.E.S. personal trainer in St. Louis, Brentwood and Clayton, MO.