Research Weighing In On Diets Finds Low-Carb, Low-Fat Plans Both Work

Atkins? Ornish? The Biggest Loser?

Branded diets are a multibillion-dollar industry, with each claiming to be superior to others. But an exhaustive analysis of nearly 50 trials involving more than 7,200 overweight and obese adults led by Canadian researchers shows the weight-loss differences between trademarked diets are minimal.

At six months, both low-carb and low-fat dieters achieved similar weight loss — about eight kilograms, on average, compared with people not on a diet. Low-carb diets (Atkins, South Beach, Zone) had a slight early edge over low-fat (Ornish, Rosemary Conley) plans, but by 12 months the differences between the two diets had mostly evaporated.

The team’s conclusion: Despite mass advertising and “expert” proclamations as to which diet is better, “weight loss differences between diets were small with little differences of clinical importance for those seeking weight loss.”

Here are five things you need to know about the study, published Tuesday in the Journal of the American Medical Association:

The appetizer:

The researchers set out to answer a simple question: Among all branded diets for which randomized controlled trial data exists, which results in the most weight loss at six and 12 months?

“At any given time, 100 million Americans are on some type of diet,” said lead author Dr. Bradley Johnston, an assistant professor of clinical epidemiology at the Michael G. De Groote School of Medicine at McMaster University in Hamilton, Ont., and a clinical epidemiologist and scientist at Toronto’s Hospital for Sick Children.

Many people are confused about the latest diet craze or “flavour of the day” that changes monthly, if not daily, he said. Given their popularity, “there has been a real lack of research (into competing diets) to examine their relative benefits,” said co-author Dr. Geoff Ball, an associate professor in the faculty of medicine and dentistry at the University of Alberta.

The starter/salad:

The team searched the literature for studies in which overweight or obese adults were randomly assigned to a branded (or “brand-like”) diet, versus no diet. (Diets were labelled brand-like when they met the definition of a trademark diet. For example, diets consisting of less than 40 per cent of calories from carbohydrates per day were considered “Atkins-like.”)

In the end, the team pooled data from 48 studies involving 7,286 individuals; the median age was 46, the median weight 94 kilograms. The studies included 11 branded diets: Atkins, Weight Watchers, Zone, Jenny Craig, LEARN, Nutrisystem, Ornish, Volumetrics, Rosemary Conley, Slimming World and South Beach. They included “moderate macronutrient” diets — diets that, give or take, involve 60 per cent carbohydrates, 15 per cent protein and 25 per cent fat.

There were a few head-to-head trials comparing various diets. But the team, which included researchers from the University of B.C., University of Ottawa, Stanford University School of Medicine in California and Tufts University in Boston, used a method that allowed them to compare diets across class and across brands that had never been compared before in randomized controlled trials.

The main course:

At six months out, people on low-carb diets lost the most (a median difference in weight loss of 8.73 kilograms) followed by those on low-fat diets (7.99 kilograms), compared with no diet. Intuitively a low-carb diet may have an edge because of the higher intake of protein, which produces a stronger “I’m full” effect than fats and carbohydrates, the researchers wrote.