Saturday, March 8, 2008

Low Carb diets - not a problem for a healthy cardiovascular system

This study came through yesterday. The researchers were looking at the effects of a very-low-carbohydrate, high-saturated-fat weight-loss diet (LC) on brachial artery flow-mediated dilatation (FMD). Reduced flow-mediated dilation, as measured in this study, is an early indicator of cardiovascular disease - the vessels are not opening up as the blood flows though - they are not "flexing".

The researchers found that this study showed that a low carb diet does not impair FMD and actually had benficial effects on most other markers of cardiovascular health.

The full abstract is copied below for you to look at.

Now that might be enough to write. However, a few days ago I put up a fairly innocuous post "Low Carb Brief" In the comments to that someone pointed me to a study reported here , the abstract of which is found here

The shock horror headline was that "Low-fat Diets More Likely To Reduce Risk Of Heart Disease Than Low-carb Diets" as those researchers found that their low carb diet diminished FMD. Stephan commented superbly on this research here:

So let me get this straight. What we're looking at is data showing that LC beat or tied LF on every relevant parameter they reported except one, and somehow that means LF diets are healthier than LC? Even though overweight and hypertension are important risk factors for cardiovascular disease? Even though trig/HDL is probably the best predictor of heart disease of any of these measures?

This article wouldn't bother me if it weren't so arrogant. If it had simply reported the facts as an interesting phenomenon, instead of tacking on a politically motivated (and incorrect) interpretation, I would have just found it interesting. But the author is bigger than his britches: "LF diets may confer greater cardiovascular protection than LC diets."

The irony isn't lost on me that the paper is published in the journal Hypertension, shows that LC diets ameliorate hypertension better than LF diets, yet somehow claims LF diets are more protective of cardiovascular disease than LC. Huh?

Unfortunately, this is typical of researchers in the diet-health field and the media that report on it.

Now there is new research that indicates that low carb diets do not affect FMD and have benefits in other areas of cardiovascular health. I wonder how Science Daily will report this one!

Effects of weight loss from a very-low-carbohydrate diet on endothelial function and markers of cardiovascular disease risk in subjects with abdominal obesity

Background: The effects of a very-low-carbohydrate, high-saturated-fat weight-loss diet (LC) on brachial artery flow-mediated dilatation (FMD) and markers of endothelial function are unknown.

Objective: The effect of an LC on markers of endothelial function and cardiovascular disease (CVD) risk was compared with that of an isocaloric high-carbohydrate, low-saturated-fat diet (HC).

Design: FMD and markers of endothelial function (n = 70) and CVD risk were measured before and after 8 wk of weight loss. Ninety-nine subjects aged 50.0 ± 8.3 y with a body mass index (in kg/m2) of 33.7 ± 4.1 completed the study.

Results: Mean (±SD) FMD did not change significantly (P = 0.55) with either diet. Pulse wave velocity improved with both diets (P < 0.01). Endothelial markers, E- and P selectin, intracellular and cellular-adhesion molecule-1, tissue-type plasminogen activator, and plasminogen activator inhibitor-1 decreased (P < 0.001), with no diet effect. Adiponectin did not change significantly. More weight (P = 0.05 for diet x time interaction) and more abdominal fat mass (P = 0.05 for diet x time interaction) were lost with the LC than with the HC. LDL cholesterol decreased more with the HC than with the LC (P < 0.05, time x diet), and C-reactive protein decreased more with the HC than with the LC (P < 0.05 for diet x time interaction). Homocysteine increased more with the LC (P < 0.01 for diet x time interaction). Folate decreased with the LC and increased with the HC (P < 0.05, time; P < 0.001 for diet x time interaction).

Conclusion: A LC does not impair FMD. We observed beneficial effects of both diets on most of the CVD risk factors measured. This trial was registered with the Australian Clinical Trials Registry as ACTR N0 12606000203550.


Chainey said...
This comment has been removed by the author.
Chris said...

Chainey - I know what you mean. Then again with all these studies, it depends on what they call low carb /high fat. From the abstract, it is not even that clear as to what the diet was....or how well people stuck to it.

I am going to try to get the full article and see what it says in a bit more detail.

My main point in putting this up was to contrast is with the other study that said there was a problem with FMD resulting from the low carb diet.

Chris said...

Chainey OK - I jut bought the whole article, $8 but worth it.

Just skimming it at the moment, but one thing I noticed - Homocysteine increased with both increased more with the low carb one, but after 8 weeks the low carb diet gave a lower absolute homocysteine level than the high carb diet.

The authors say that " is not known whether such small increases in this low range have any detrimental affect on CVD risk". They certainly do not sound worried about it!

Regarding folate levels they note that there was a recent meta-analysis that concluded that folic acid did not reduce the risk of CVD anyway.

If you are interested in this I'd definitely splash out on the full article! Suffice it to say that the researchers did not have any concerns about the impact of the low carb diet on CV health

Stephan said...

Interesting, thanks for checking that out. I was wondering about the homocysteine, CRP and folate too.

That's one thing I wish they'd be more explicit about, talking about baseline along with changes in the things they measure.

There was some of that going on in the flow-mediated dilation study too, I put a little blurb about it in the comments on my post. Basically the FMD changes were probably BS too.