Saturday, January 30, 2010

Who pays the piper. High fat diet drops HDL!

From the discussion of Bradley and Hunter's 2009 paper:

"A major concern associated with low-carbohydrate diets is that the reciprocal increase in dietary fat intake, particularly if this includes saturated and trans fat, may have detrimental effects on cardiovascular risk"

Who mentioned trans fats? To find out what the diets were actually like we need to look at Table 1:




Hard to say, but there are a few rather commercial sounding foods listed where we might find trans fat. How about the nutrient breakdown on the diet, that's here:




It looks like 60% of calories from fat in the LC group, 21% saturated, 21% monounsaturated and 13% polyunsaturated.

Now hang on, 21+21+13 does not equal 60. What was the other 5%? This was a study in which university nutritionists were providing the food. They should be able to make three numbers add up. It's not as if we are working with food frequency questionnaires or dietary recall from a year ago. As they say in the methods:

"Volunteers attended on alternate days throughout the study and were supplied with all appropriate foodstuffs (preweighed into daily portions) for their particular diet"

So 5% of the fat in the LC diet was not supplied in a form which could be listed comfortably in Table 4. Anyone for trans fats?

So lets go and look to see if there is any other evidence of trans fats as 5% of calories. We can try looking in Table 5.




Hands up who knows what saturated fat does to your HDL level? OK, go to the top of the class. The LC arm increased their saturated fat intake from 15% to 20% of a few less calories, with a similar increase in monounsats too, yet they DROPPED their HDL from 1.47mmol/l to 1.35mmol/l. Not catastrophic, just bad (if you believe in lipids being good or bad, all this means to me is that they fed trans fats as well as a little extra saturated fat). In just 12 people this is not STATISTICALLY significant. At a population level it would be biologically significant.

Of course the low fat folks dropped their HDL from 1.40mmol/l to 1.15mmol/l. Statistically (p=0.01) and biologically significant. Just what anyone would expect from a low fat diet, except that the drop seems even worse than you would expect from an ordinary university designed low fat diet! Table 4 suggests 4% unlistable fats for the low fat group too.

Trans fats shared equally? I don't know.

At this point I would just like to suggest that in NO WAY should ANYONE ever let a Belfast nutritionist design their diet. Just say NO.

Stick to eating Food.

Peter

3 comments:

Jim Purdy said...

"Stick to eating Food."

You could have expanded that into 64 "Food Rules" and made it into a best-selling book.
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LeenaS said...

Oh, well, lets not blame the belfastians too much. There is a tradition of leaving "a hole" big enough for trans fats to crawl in, so that no-one needs to mention such ugly names.

A good bad example is the big and prestigious DASH, more than a decade ago. Pity.

O Primitivo said...

Low HDL Cholesterol is Associated with Lower Gray Matter Volume in Cognitively Healthy Adults. - http://www.ncbi.nlm.nih.gov/pubmed/20725527