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Low Fat Vs Low Carb Diets?

Posted Sep 21 2010 7:17am

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

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

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

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 been 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

Thank you – Dr Stephen Chaney for the above commentary.

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