Sunday, July 22, 2012

The Nutrition Debate #60: Dietary Composition: Dr. Ludwig’s (et. al.) Study

Everybody’s talking about it. David S. Ludwig, MD, PhD, and colleagues at New Balance Foundation Obesity Prevention Center (Harvard), and Children’s Hospital, Boston, and Brigham and Women’s Hospital, Boston, and Baylor College of Medicine, Houston, and Vanderbilt University, Nashville, published the results of a well-designed, four-year study on June 27, 2012, in the Journal of the American Medical Association (JAMA). The purpose was to study “the effect of dietary composition on energy expenditure during weight-loss maintenance “(my emphasis).
Almost simultaneously (on June 30, 2012), the New York Times published an opinion piece, "What Really Makes Us Fat," loosely based on the study. In it, award winning science writer Gary Taubes, says, “What was done by Dr. Ludwig’s team has never been done before.” He concludes his piece with, “The public health implications are enormous.”
This study begins after all the participants had achieved a 10% to 15% weight loss by a calorie restricted (60%) “run-in” diet. In random order, each for 4 weeks, the participants ate three isocaloric (2,000kcal/d) diets: 1) a low-fat diet (60% carbs, 20% fat, 20% protein, high glycemic load); 2) a low-glycemic index diet (40% carbs, 40% fat and 20% protein, moderate glycemic load); and 3) a very-low carb (Atkins) diet (10% carb, 60% fat and 30% protein, low glycemic load).
The JAMA authors conclude: “Our study demonstrates that commonly consumed diets can affect metabolism and components of the metabolic syndrome in markedly different ways during weight-loss maintenance, independent of energy content. The low-fat diet produced changes in energy expenditure and serum leptin that would predict weight regain. In addition, this conventionally recommended diet had unfavorable effects on most of the metabolic syndrome components studied herein. In contrast, the very low carbohydrate diet had the most beneficial effects on energy expenditure and several metabolic syndrome components…” (both HDL and triglycerides, I noted).
Energy expenditure, the primary outcome measure of the study, was measured by state-of-the art stable isotope analysis at Baylor. This outcome was especially stunning: “The results of our study challenge the notion that a calorie is a calorie from a metabolic perspective,” the authors state. “Total Energy Expenditure differed by approximately 300 kcal/d between these 2 diets” (very low carb and low fat), “an effect corresponding with the amount of energy typically expended in 1 hour of moderate-intensity physical activity.”
In other words, as Taubes explains in his NYT article, “…when the subjects were eating low-fat diets, they’d have to add an hour of moderate-intensity physical activity each day to expend as much energy as they would effortlessly on the very-low-carb diet. And this while consuming the same amount of calories. If the physical activity made them hungrier – a likely assumption – maintaining weight on the low-fat, high-carb diet would be even harder,” Taubes wrote.
Taubes then posits, “If we think of Dr. Ludwig’s subjects as pre-obese, then the study tells us that the nutrient composition of the diet can trigger the predisposition to get fat, independent of the calories consumed. The fewer carbohydrates we eat, the more easily we remain lean. The more carbohydrates, the more difficult. In other words, carbohydrates are fattening, and obesity is a fat-storage defect. What matters, then, is the quantity and quality of carbohydrates we consume and their effect on insulin.”
Ludwig’s subjects are, frankly, “pre-obese.” As the study states, “only 1 in 6 overweight and obese adults report ever having maintained weight loss of at least 10% for 1 year.” Taubes reasonably says Ludwig’s subjects are “almost assuredly going to get fatter, so they can be research stand-ins for those of us who are merely predisposed to get fat but haven’t done so yet and might take a few years or decades longer to do it.”
Taubes then concludes, “From this perspective, the trial suggests that among the bad decisions we can make to maintain our weight is exactly what the government and medical organizations like the American Heart Association have been telling us to do: eat low-fat, carbohydrate-rich diets, even if those diets include whole grains and fruits and vegetables.”
You could read this report in JAMA and have a different take-away; this blog piece is just the way I see it. Call it my bias, or see it as good science “that has never been done before” (as per Taubes). Like all good science, it is controversial and in need of replication by independent investigators, as Taubes states. I knew that’s why I like this guy. And he gets an Op-Ed (and a couple of Sunday Magazine cover stories) in the New York Times, which must still have a few movers and shakers among its readers.
© Dan Brown 7/22/12

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