Imagine Banting’s delight if he could listen in on a 21st-century cocktail party. Thanks to Dr. Robert Atkins, the cantankerous cardiologist who revived Banting’s theories in the 1970s, most people now assume that carbohydrates are part of the problem. We don’t “diet” anymore. We “go on Atkins,” trusting that bunless burgers will do for us what fat-free doughnuts never did. Our faith is not entirely misguided. It’s now clear that carb-rich foods can inflate appetite and foster type 2 diabetes, and that low-carb diets promote short-term weight loss. But healthy eating is not quite as simple, or as boring, as living on fat and protein. The truth is, you can have your carbs and eat them, too. You just have to know how to choose them.
When Atkins came out against bread, potatoes and pasta 30 years ago, nutritionists dismissed him as a crank. Fat was the demon of the day, and carbohydrates were seen as their exorcist. But many experts now believe that Atkins was at least half right in condemning carbohydrates. Last year five well-designed clinical trials indicated that low-carbohydrate diets were as good as low-fat diets–and in most cases better–for helping very overweight people shed kilos quickly. Study participants stuck better with low-carb diets than with low-fat diets. And though low-carb dieters increased their fat intake, they enjoyed reductions in LDL (“bad”) cholesterol and triglycerides (fat-carrying particles associated with heart disease), and increases in HDL (“good”) cholesterol.
Granted, short-term weight loss is not the best measure of a diet’s ultimate value. There is still no clear evidence that Atkins-style diets are better than any others for helping people stay slim, and their broader health effects are still unknown. Will moderately overweight people enjoy the same improvements in triglyceride and HDL levels as the obese study participants? Could the abundant protein in an Atkins-style diet cause kidney damage or bone loss over time? These important questions deserve answers. But the case against carbs doesn’t rest entirely on weight-loss trials. Other recent research shows that certain carb-rich foods can cause extreme surges in blood sugar and insulin spikes that contribute to weight gain; they also increase your risk of developing diabetes and heart disease.
The Atkins diet, in its cruder variants, assumes that any food rich in carbohydrates will trigger this toxic cascade. But carbs differ greatly in their potential to do this. The key variable is the glycemic index, a ranking of foods according to how rapidly their sugars are released into the bloodstream. The body converts all digestible carbohydrates into glucose, the sugar that our cells use as fuel. When glucose molecules pass from the gut into the bloodstream, the pancreas releases insulin, a hormone that activates cells to absorb it. Muscle, fat and other cells then sponge the excess glucose from the blood, and insulin levels return to normal. The concept of a glycemic index emerged in the 1990s, when researchers at the University of Toronto showed that some foods (cornflakes or potatoes, for example) raised blood sugar faster and higher than others (oatmeal or brown rice), placing greater demands on the insulin system. That discovery led to an even more useful measurement called glycemic load, which considers both a food’s glycemic index and how much carbohydrate the food delivers in a single serving. Most fruits, vegetables, beans and whole grains have low glycemic loads: their sugars enter the bloodstream gradually, triggering only a moderate rise in insulin. But when fruits are squeezed into juices, or grains are pulverized into fine flour, they become the equivalent of sugar water.
After a snack or meal with a high glycemic load, blood-sugar levels rise higher and faster than after a meal with a low load. The insulin needed to stuff all that sugar into muscle and fat cells also blunts the activity of glucagon, a hormone that signals the body to burn stored fuel when blood-sugar levels fall below a certain point. Glucose levels plummet as a result, leaving the brain and other tissues starved for energy. Concentration flags, muscles get shaky and the body perceives an emergency. In search of a quick fix, the gut and brain send out hunger signals. If you respond to them by downing another high-glycemic-load snack, the cycle repeats itself.
Foods with a high glycemic load pose another problem. The tissues of people who are overweight or physically inactive resist insulin’s signal to pull in glucose from the blood–a condition known as insulin resistance. This keeps blood sugar at high levels for prolonged periods. It also forces the pancreas to produce extra insulin, leading ultimately to diabetes.
The good news is that you needn’t swear off carbohydrates to avoid these problems. The trick is to choose foods with low glycemic loads. But you don’t have to carry a food chart to eat wisely. Here are some rules of thumb for choosing the best carbs:
EAT PLANTS. Eaten whole, most fruits and vegetables have a modest effect on blood sugar and insulin. They also deliver fiber and other healthful nutrients. Starchy vegetables such as potatoes and corn have high glycemic loads, so use them sparingly. Most fruit juices contain too little fruit, too much sugar and too many empty calories.
BANK ON BEANS. They’re an excellent source of protein. They are rich in fiber, vitamins and other micronutrients, and have a small effect on blood sugar and insulin.
GO NUTS. Almonds, hazelnuts, peanuts, pecans, pistachios and walnuts are great low-carb alternatives to crackers, chips or pretzels made with refined flour. Walnuts also have heart-healthy omega-3 fats. Keep in mind that at 185 calories per 28 grams, eating a handful of walnuts a day without cutting back on anything else could make you gain four kilograms during the course of a year.
CHOOSE THE BEST FATS. Fats tend to slow the passage of food from the stomach to the intestine. So eating good fats with a carbohydrate–olive oil with bread, for example–can curb increases in blood sugar. Good fats are unsaturated fats, such as those found in vegetable oils (olive, canola, peanut, corn, soybean), fatty fish, nuts and avocados.
SWITCH TO WHOLE GRAINS. Until the 19th century, humans ate grains either whole or roughly ground. In this form, grains offer a carbohydrate package rich in fiber, healthy fats, vitamins, minerals, plant enzymes and many other nutrients. Today’s refined grains–white bread, white rice and many breakfast cereals–have a higher glycemic load. Fortunately, whole grains are making a comeback. There are at least a dozen options, from brown rice and cracked wheat to quinoa and spelt. Make a habit of starting the day with a bowl of whole-grain cereal. And don’t give up on pasta. Whole-wheat pasta is now more widely available.
Can you eat all these carbs and still lose weight? Consider a recent study of overweight teens at Children’s Hospital in Boston. One group was assigned to an all-you-can-eat diet that emphasized fruits, vegetables and whole grains, and reduced carbohydrates to about 45 percent of total calories. The other group was encouraged to limit overall food intake and reduce fat, so that carbohydrates supplied between 55 and 60 percent of calories. The teens on the first diet lost more weight and body fat–and stayed slimmer–than those on the second. But weight control is only one benefit of eating the right carbs. Several studies suggest that people who eat two to three servings of whole grains a day are less likely to develop heart disease, diabetes and digestive problems such as diverticulitis and constipation.
Robert Atkins deserves credit for publicizing the perils of refined carbohydrates, but the centerpiece of the original Atkins diet–eating unlimited amounts of beef, sausage, butter and cheese–is not a prescription for optimal health. A diet that includes fish, poultry, beans, nuts, fruits and vegetables, whole grains and vegetable oils can work for weight control even as it reduces the risks of disease. In other words, it can bring you greater benefits than any medicine yet invented. It tastes better, too.
