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 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 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.
However, during months seven through 12, the difference between the two diets was virtually lost (7.25 kilograms for low-carb versus 7.27 kilograms for low-fat.) The weight-loss differences between individual diets also were minimal. For example the Atkins diet resulted in an estimated weight loss of 1.7 kilograms more than the Zone diet at the six-month follow-up.
Overall, the Ornish, Rosemary Conley, Jenny Craig and Atkins diets were associated with the largest weight loss at 12 months. Even then, “there was nothing that stood out in terms of huge differences” between diets, Johnston said.
Only five trials — all evaluating the Atkins diet — reported side effects; most were mild to moderate (such as constipation, headache and halitosis, or bad breath) and went away on their own. But, in an accompanying editorial, Linda Van Horn of the Northwestern University Feinberg School of Medicine in Chicago raised concerns about possible long-term effects of high-protein diets on kidney function and calcium loss after months or years on the diet.
People lost more on programs that included individual or group support or counselling (an extra three kilograms at six months). Those who exercised lost 0.64 kilograms more, on average, after six months, and three kilograms, on average, at the 12-month follow-up.
The researchers didn’t look at other health outcomes, such as effects on cholesterol or blood pressure. However, “If you’re only interested in weight loss, these types of diets work over the short term,” Johnston said.
People shouldn’t select a diet based on what they see on television, but rather what they feel they can stick with, he said. Ultimately the goal should be making long-term lifestyle changes so that any lost weight isn’t regained, Johnston said.
The paper “basically tells us that if you want to lose weight you’ve got to reduce calories and keep them reduced,” said Dr. Yoni Freedhoff, medical director of the Bariatric Medical Institute in Ottawa, who wasn’t involved in the study.
Despite the hype and hyperbolic news releases touting one diet over another, “So long as the diet helps (people) to reduce their calories and the person likes it enough to sustain it, they’re probably good to go.”