Take your pick: All diets work
Reported February 26, 2009
Low-carb? High-protein? Or low-fat? If you’re planning to shed some pounds, you can stop fussing over which diet works best, according to a study published in the New England Journal of Medicine.
Researchers at the Harvard School of Public Health randomly assigned 811 overweight adults to four different diets with varying ratios of fat, carbohydrates and protein, then measured their weight loss at six months and two years.
“All the diets we tested produced weight loss to the same extent,” says the study’s lead author, Frank Sacks, a medical doctor and professor in the school’s department of nutrition. “No one diet was better for reducing calories or increasing weight loss at six months or two years.”
The four heart-healthy diets – all of which were low in saturated fat and cholesterol and high in dietary fibre – were designed to cover many of today’s most popular options:
Low-fat, average-protein: 20 per cent of calories from fat, 15 per cent from protein, 65 per cent from carbohydrates.
Low-fat, high-protein: 20 per cent fat, 25 per cent protein, 55 per cent carbs.
High-fat, average-protein: 40 per cent fat, 15 per cent protein, 45 per cent carbs.
High-fat, high-protein: 40 per cent fat, 25 per cent protein, 35 per cent carbs.
Calorie counts were assigned individually to each dieter based on subtracting 750 calories from their daily caloric needs. Participants were asked to attend group sessions and use self-monitoring tools, such as diaries. They were also asked to exercise moderately for 90 minutes a week.
At the six-month mark, participants assigned to each diet had lost an average of 13 pounds (six kilograms). Among the 80 per cent who completed the program, the average weight loss was nine pounds (four kilograms) at two years. Waistlines were reduced by an average of two inches at the end of the two-year period.
All the diets improved cardiovascular risk factors in the participants, with a few subtle differences that dieters may want to discuss with their doctors. For instance, lower-fat diets reduced LDL cholesterol a little more than the higher-fat diets.
Although none of the four diets were as extreme as some of today’s trendy diets, such as the high-protein, low-carb Atkins, Dr. Sacks says his findings show there is “nothing magic about them.”
Still, he isn’t saying they’re useless. “Some people like one of these popular diets and if it works for them, all the better.”
But for others, a less-rigid approach can work just as well. “It gives people a lot of flexibility to try a diet that’s comfortable for them, [that] they feel they can stick with, and to focus on calories, not the particular type of content of diet.”
If there is magic to be had, it’s in motivation. Dr. Sacks found that rather than the ratios of fats to proteins, it was other factors, most notably the counselling sessions participants attended, that most affected dieting success. On average, people who attended sessions lost more weight than those who didn’t, he says.
“The biggest influence is in the individual response, not the diet type,” he says. “That’s something we ought to delve into and understand better.”
In an editorial appearing in the same issue of the journal, diet researcher Martijn Katan, from the Institute of Health Sciences at VU University, Amsterdam, suggests that Dr. Sacks’s findings illustrate the need for a societal, rather than individual, approach to combatting growing obesity rates.
He cites a French study that examined a town that implemented a number of community-based efforts to encourage children to eat better and exercise more, including building sports facilities and offering cooking workshops to families. In five years, the prevalence of overweight children had dropped to 8.8 per cent, compared with 17.8 in neighbouring towns.
“Like cholera, obesity may be a problem that cannot be solved by individual persons but that requires community action,” Dr. Katan writes.
Dr. Sacks agrees with this sentiment, but he says a two-pronged approach taking both the individual and the community into account may be best.
“There are two equal parts to this,” he says. “We should try to find out why some people can do very well and some not. There may be biological factors we don’t know about.”