After analysing eight popular diets, he and his team found that the Ornish plan, the Weight Watchers High-Carbohydrate diet and the New Glucose Revolution plan came out on top in terms of nutritional quality and potential effects on heart health.
All of the diets included high amounts of fruits, vegetables and fibre and small quantities of artery-clogging types of fat.
"Obese people already have a higher risk of heart disease," Ma said, adding that it is particularly important that they make heart-healthy diet changes that can be kept up for the long haul.
The Atkins plan, a high-protein, low-carbohydrate diet, came at the bottom of the list, mainly because of its more liberal attitude toward red meat, saturated fat and trans fats, and low amounts of fruit and fibre.
The findings are published in the Journal of the American Dietetic Association.
The researchers used a measure called the Alternate Healthy Eating Index (AHEI) to judge the quality of the widely used diet plans.
They picked six of the diets from the New York Times bestseller list and also included the Weight Watchers plan, as it is the largest commercial plan in the United States, as well as the federal government's 2005 Food Guide Pyramid, since it offers diet guidelines to all Americans.
The AHEI evaluates a diet's potential heart benefits based on factors such as the amount of fruits, vegetables and fiber, and the ratio of heart-healthy polyunsaturated fats to cholesterol-raising saturated fat.
The top score went to the Ornish diet, a low-fat, largely vegetarian plan that allows some non-fat dairy and egg whites. The diet, developed by Dr. Dean Ornish, is intended to prevent and treat heart disease, so its high score – 64.6 out of a possible 70 points – is not unexpected.
Also scoring well, at just over 57 points, were the Weight Watchers High-Carbohydrate and the New Glucose Revolution diets –which, like Ornish, contain high amounts of fruits, vegetables and fibre-rich grains.
The Glucose diet is based on the concept of the glycemic index. It limits simple carbohydrates that cause quick blood-sugar spikes – like potatoes and white bread – but allows complex carbohydrates higher in fibre and other nutrients.
The Atkins plan and some other low-carb, high-protein diets, including the Weight Watchers High-Protein option, were deemed less heart-healthy.
Surprisingly, Ma said, the government's Food Pyramid landed in the middle. Although the Pyramid was revamped in 2005, it still falls short of the top-ranked diets as far as fruits, vegetables, fibre and limits on "bad" fats, Ma added.
The researchers are not advocating any one particular brand of weight-loss plan. But, according to Ma, people who are trying to lose weight can look to the components of the top-scoring diets to help fashion a heart-healthy eating plan.