This is the kind of study I want to see. And still, ARGH! “Effects of Low-Carbohydrate and Low-Fat Diets: A Randomized Trial“:
Background: Low-carbohydrate diets are popular for weight loss, but their cardiovascular effects have not been well-studied, particularly in diverse populations.
Objective: To examine the effects of a low-carbohydrate diet compared with a low-fat diet on body weight and cardiovascular risk factors.
Design: A randomized, parallel-group trial. (ClinicalTrials.gov: NCT00609271)
Setting: A large academic medical center.
Participants: 148 men and women without clinical cardiovascular disease and diabetes.
Intervention: A low-carbohydrate (<40 g/d) or low-fat (<30% of daily energy intake from total fat [<7% saturated fat]) diet. Both groups received dietary counseling at regular intervals throughout the trial.
Measurements: Data on weight, cardiovascular risk factors, and dietary composition were collected at 0, 3, 6, and 12 months.
For decades, it’s been fat is gonna kill you. It’s the red meat, it’s the butter, it’s the bacon. Then along came some crazies who said it was the carbs instead. So we tried to reduce carbs, but I mean you’ve got to eat something! So which is better? A low carb or a low fat diet?
This was a randomized controlled trial of a low carb (< 40g/d) versus a low-fat (<30% daily calories from fat and <7% saturated fat) diet. Those are defined differently, so let’s try this. Those in the low-carb diet obtained about 30% of their calories from carbs. Those in the low-fat diet shot for 30% of their calories from fats.
Outcomes included weight, risk factors for cardiovascular disease, and compliance with the diet. The percentage of people who completed the study in each arm was about 80%, which is pretty good. Who won?
Well, it turns out that people on the low-carb diet lost, on average, more weight – about 7.7 pounds more over a year. They also had more of a fat loss (1.5%). Their ratio of total-HDL cholesterol improved more. Their triglyceride levels fell more. Their HDL cholesterol levels went up more. In terms of 10-year Framingham risk scores, those on the low-carb diet saw significant decreases, while those on the low-fat diet did not.
So in pretty much every metric you could pick, the low-carb diet beat the low-fat diet.
But I expect to see the usual “caveats” in the media. They’ll warn us that even though cholesterol levels improved on the low-carb diet, that eating more fats just simply must be bad for you. They’ll repeat how Framingham risk scores and risk factors aren’t the same as actual bad outcomes, while using those same factors to promote low-fat diets as “better”. And, they’ll attack this RCT for being only one year in design, while ignoring that almost all their data is observational.
The 2010 Dietary Guidelines for Americans recommend that 45-65% of our diets be from carbohydrates, and that 20-35% be from fats. In essence, they recommend a low-fat diet for everyone, and a low-carb diet for none. Will the 2015 Dietary Guidelines for Americans be any different?
UPDATE: Also, there’s this:
While the low-fat group did lose weight, they appeared to lose more muscle than fat.
“They actually lost lean muscle mass, which is a bad thing,” Dr. Mozaffarian said. “Your balance of lean mass versus fat mass is much more important than weight. And that’s a very important finding that shows why the low-carb, high-fat group did so metabolically well.”
