In the post-Atkins era, this might seem like strange advice: Eat carbohydrates to help you stay lean. But according to a study of 4,451 healthy Canadians, those whose diets contained the most carbohydrate had the lowest risk of being overweight or obese.
For the past decade, the debate over the best diet to maintain a healthy weight has been centred around carbohydrates. The late physician and cardiologist Robert Atkins won over many dieters to his high-protein, low-carbohydrate plan which, over the short term, produces greater weight-loss results than a diet high in carbohydrates.
But the long term is what counts when it comes to maintaining a healthy weight and studies have determined there's no difference between the diets and amount of weight lost after one year.
In fact, recent studies suggest that a high carbohydrate diet is indeed effective for losing weight and outperforms a high protein diet when it comes to losing body fat and lowering cholesterol and blood sugar.
The current study, published in the July issue of the Journal of the American Dietetic Association, assessed the diets and body weights of 4,451 healthy Canadians aged 18 years and older. The likelihood of being overweight or obese declined steadily as carbohydrate intake increased.
Compared to people whose diets provided the least carbohydrate (36 per cent of calories), those who consumed the most (64 per cent of calories) had a 40 per cent lower risk of being overweight or obese.
Overweight and obesity was defined as having a body mass index (BMI) of 25 or greater. (BMI is calculated as your weight in kilograms divided by the square of your height in meters. For adults, a BMI of 25 or more signals overweight; 30 more indicates obesity.) A higher carbohydrate diet was protective from overweight and obesity among older and younger participants, men and women, and people who never smoked.
A diet that is high in carbs such as whole grains, legumes, fruits and vegetables is also naturally low in fat and high in fibre. Fibre-rich foods add volume to meals, helping you feel full on fewer calories.
In the study, participants with the highest carbohydrate intake had a lower intake of calories, protein, total fat and saturated fat than the lower carbohydrate eaters. They also consumed almost double the fibre and more fruits and vegetables that those with the lowest carbohydrate intake.
Earlier research has also revealed that a high carbohydrate diet is good for the waistline. A 2008 study found that the Mediterranean diet - high in whole grains, fruit and vegetables - was as effective as the low carbohydrate diet at shedding pounds over a two-year period. What's more, among people with diabetes, this high carbohydrate diet did a better job at reducing blood sugar and insulin levels.
However, not all carbohydrates are good for you. Mounting evidence suggests that diets based on low glycemic index (GI) carbohydrates are better for weight control and health.
The GI is a scale that ranks carbohydrate-rich foods by how quickly they are digested and raise blood sugar compared to pure glucose. Foods that are ranked high on the GI scale are fast acting - they're digested quickly and, as a result, cause large rises in blood sugar and insulin, the hormone that removes sugar from the blood and stores it in cells. Examples include white bread, whole-wheat bread, baked potatoes, refined breakfast cereals, instant oatmeal, cereal bars, raisins, ripe bananas, carrots, honey and sugar.
Foods with a low GI release sugar more slowly into the bloodstream and don't produce an outpouring of insulin. Examples include grainy breads with seeds, steel cut oats, 100 per cent bran cereals, oat bran, brown rice, sweet potatoes, pasta, apples, citrus fruit, grapes, pears, legumes, nuts, milk, yogurt and soymilk.
In a recent study of 129 overweight adults assigned to one of four diets that differed in the amount of carbohydrate and glycemic index found that while all diets promoted weight loss, only the high carb, low glycemic index diet resulted in a greater loss of body fat and a reduction of LDL (bad) cholesterol.
It's thought that a diet based on high glycemic carbohydrates is less effective at promoting weight loss because the large spikes in blood sugar and insulin it causes can trigger hunger and inhibit the breakdown of body fat.
To help reduce the risk of excess weight gain, diabetes and heart disease, 40 to 65 per cent of your daily calories should come from carbohydrate rich foods such as whole grains, fruit, vegetables and legumes. The following strategies can help you increase your intake of healthy carbs - and manage your weight.
Go for whole grain
Choose 100 per cent whole grain breads, brown rice, whole wheat pasta, quinoa and breakfast cereals made from whole grains. Read ingredient lists; choose foods that list a whole grain as the first ingredient.
Choose fibre-rich carbs
Include 21 to 38 grams of dietary fibre in your daily diet. Men and women aged 19 to 50 need 38 and 25 grams of fibre each day, respectively. Older women require 21 grams; older men need 30 grams.
Choose breads that provide at least 2 grams of fibre per slice and breakfast cereals with at least 5 grams of fibre per serving. Mix ½ cup (125 ml) of 100-per-cent bran cereal with other cereals to boost your fibre intake.
Add legumes and lentils to soups, salads and pasta. Snack on fruit, dried fruit, nuts or plain popcorn instead of refined, low fibre snacks such as pretzels, cereal bars, and white crackers.
Choose low glycemic
In general, whole grains, bran cereals, legumes, fruits and vegetables have a low glycemic index. Include at least one low GI food per meal, or base two of your meals on low GI choices.
Instead of creamy dressings, use salad dressings made from vinegar or lemon juice - the acidity will result in a further reduction in the GI of your meal. Choose fruits that are more acidic (e.g. oranges, grapefruit, cherries, strawberries, green apples) as these have a low GI.
Practice portion control
Regardless of the type of carbohydrate you eat, managing portion size is key to weight control. If you are trying to lose weight, keep portions of cooked grains and pasta to 1 to 1.5 cups (250 to 375 ml) - or fill only one-quarter of your plate with starchy foods. To judge your portion size at home, measure your food for a few days.
Choose two slices of whole grain bread instead of one large bagel (worth 4 to 5 slices of bread).
Limit refined sugars
Curb your intake of candy, chocolate, soft drinks, fruit drinks, desserts and other sweets. The World Health Organization recommends limiting added sugars to no more than 10 per cent of daily calories. If you follow a 2,000-calorie diet, this translates to a daily maximum of 48 grams (12 teaspoons worth) of added sugars.
Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV's Canada AM every Wednesday. Her website is lesliebeck.com.