Tuesday, September 21, 2010
By Dr. Stephen Chaney, Phd
You would think the question of low carb versus low fat diets would be settled by now. Literally dozens of studies have been published on the subject and they are all in pretty much agreement that initial weight loss (mostly water) is faster on the low carb diets but that weight loss at one or two years is essentially the same on the two diets.
The unique feature of the study just published in Annals of Internal Medicine (153: 147-157, 2010) was that it included an intensive behavior modification program to optimize the weight loss over the two year period of the study.
Here is how the study was conducted:
The low-carbohydrate group was instructed to eat no more than 20 grams of carbohydrate per day for 3 months and then to increase the carbohydrate by no more than 5 grams per day each week until they achieved their desired weight.
The low-fat group was instructed to decrease calories and restrict fat intake to no more than 30% of calories. All of the patients were enrolled in a lifestyle program designed to help them improve their physical
activity and other lifestyle factors.
The program met weekly for 20 weeks, every other week for another 20 weeks, and then monthly for the rest of the 2-year study. In short, this was a very good behavior modification program. Weight, blood pressure, blood lipid levels and side effects were measured at the beginning of the program and at 3, 6, 12 and 24 months.
Considering the enormous effort put into behavior modification, the results of this study were somewhat
disappointing. The participants lost an average of only 22 pounds and the end of year one and had gained back 7 of those pounds by the end of year two. And that only included the ~50% who stayed with the
program for the whole two years. Who knows how much weight was gained by the people who dropped out of the study?
Since the behavior modification program used in this study did not significantly impact either weight loss or weight maintenance, it's perhaps not surprising that the other findings of this study are pretty much the same as the findings from previous studies. Weight loss was slightly greater in the low carb group at 6 months, but did not differ significantly between the two groups at either 1 year or two years. Triglyceride levels and blood pressure were lower for the low carb group at 6 and 12 months, but were the same for both groups at 2 years.
The only significant differences between the two groups at 2 years were LDL (bad) cholesterol levels - which
were significantly lower in the low fat group - and HDL (good) cholesterol levels - which were significantly
higher in the low carb group.
Ironically, I've already seen blogs from proponents of the low carb diets trumpeting the increase in HDL levels as "proof" that low carb diets are better for your heart. But, it's not just HDL or LDL that's important, it's the ratio of total cholesterol to HDL cholesterol that determines your risk of heart disease. And at two years the ratio of total cholesterol to HDL cholesterol was virtually identical on the two diets.
As for side effects, the patients on the low carb diet reported more constipation and more problems with bad
breath. If you've beeen on a low carb diet before, that's probably not news to you.
So what is the take home message from this study?
1) The laws of thermodynamics still work. It's all about calories in versus calories out. Low carb and low fat diets work equally well for weight loss.
2) If you just focus on blood lipid levels and blood pressure there is also no significant difference between the two diets.
However, I still recommend against high fat (low carb) diets as a long term lifestyle strategy. We know that high fat diets are much more likely to cause inflammation - which is a risk factor for
multiple diseases. We also know that long term consumption of high fat diets is associated with increased risk of heart disease, certain types of cancers & diabetes.
To Your Health!
Dr. Stephen G Chaney