While the study focused primary on diet, the participants were also given 22 health education classes and were encouraged to meet standard guidelines for physical activity.
Gardner designed the study with fellow researchers to examine how overweight and obese people would compare when consuming low-carbohydrate and low-fat diets. The recruited individuals -- who hailed from northern California -- were split into two groups: "healthy" low-carb and "healthy" low-fat. Both groups attended courses led by dietitians who instructed them to consume minimally processed and nutrient-rich whole foods. They also encouraged participants to cook at home on a regular basis.
Individuals in the low-fat group were told to eat foods such as brown quinoa, fresh fruit, legumes, rice, barley, steel-cut oats, lentils, lean meats and low-fat dairy products. Although soft drinks, fruit juice, white rice and white bread may technically be low in fat, participants were told to avoid these, as they are highly processed or contain added sugars. The low-carb group was advised to eat foods such as avocados, hard cheeses, vegetables, olive oil, salmon, nut butter, and grass-fed and pasture-raised animal foods.
"We told everybody they should buy whole foods. Nobody should have foods with refined sugar. They suck," Gardner told NBC News.
"Also, we advised them to diet in a way that didn't make them feel hungry or deprived -- otherwise it's hard to maintain the diet in the long run,” he said.
After one year, both groups demonstrated significant weight loss even though they didn't worry about their calorie intake. Those in the low-fat group lost about 11.7 pounds on average, while the members of the low-carb group lost a little more than 13 pounds. Individuals in both groups also showed improvements in other important health markers such as reduced body fat, lower blood sugar, improved blood pressure levels and decreased waist size.
"This is the road map to reducing the obesity epidemic in the United States," Dr. Dariush Mozaffarian, a cardiologist and dean of the Friedman School of Nutrition Science and Policy at Tufts University, who was not involved in the new study, told The New York Times. "It's time for the U.S. and other national policies to stop focusing on calories and calorie counting."
Beyond calorie counting, the study contradicted the increasingly popular theory that diets should be catered to an individual's genetics. According to U.S. News and World Report, previous research has suggested that certain genes or an individual's insulin levels could interact with different diets to affect weight loss.
This new study showed no significant difference when filtering for such factors. Weight loss among the participants was found to be the same, regardless of genetics, insulin levels or diet type.
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"The bottom line: Diet quality is important for both weight control and long-term well-being," Dr. Walter Willett, chairman of the nutrition department at the Harvard T. H. Chan School of Public Health, told The New York Times.
Read the new research at jamanetwork.com