Tuesday, March 23, 2010

BBC article's advice: Replace saturated with polyunsaturated fats

The BBC article is here. It is based on meta-analysis of eight previous studies conducted by Harvard researchers, which the article states cover more than 13,000 people. The article also says that: “… [saturated] fats raise the levels of bad cholesterol that block the arteries to the heart.” They are of course referring to LDL cholesterol as the "bad cholesterol".

Sourcing bias is a notorious problem with meta-analyses (i.e., the choice of studies to use in a meta-analysis). Another problem is that you cannot tell what the studies sourced controlled for. Consider a study that compares health markers for smokers and non-smokers, where the smokers eat more saturated fat than the non-smokers. This study may confuse the effect of smoking with that of saturated fat consumption. To be reliable, the study must analyze the effect of saturated fat consumption, controlling for smoking habits.

There are other statistical issues to be considered in meta-analyses. For example, some of the sourced studies may take nonlinear relationships into consideration and others not. In multivariate analysis studies, nonlinearity may lead to significantly different results from those obtained through more conventional linear analyses.

Finally, reaching misleading results with sound statistical analyses is not that hard. As my age went from 1 to 20 years, my weight was strongly correlated with the price of gasoline. Yet, neither my weight caused the price of gasoline, nor the other way around. When you look at an individual study, not a meta-analysis, you can at least try to identify the possible sources of bias and mistakes.

Having said that, a solid refutation of the main argument in the article can be made from many angles. Here is a simple refutation based on what I would call the “HDL cholesterol angle”, with links to posts and various refereed publications:

- Increasing HDL cholesterol levels, especially beyond 60 mg/dl, dramatically decreases the risk of heart disease; and this is an almost universal effect in humans. This reduction in risk occurs even for people who suffer from diabetes and familial hypercholesterolemia. The latter is a genetic condition that is associated with very elevated LDL cholesterol and that is rare, typically afflicting 1 in 500 people in its heterozygous (and most common) form.

- Increasing consumption of saturated fats (present in: lard, fatty meat, coconut oil) and dietary cholesterol (from: fish, organ meats, eggs), while decreasing consumption of refined carbohydrates (e.g., pasta, white bread) and sugars (e.g., table sugar, high fructose corn syrup), significantly increases HDL cholesterol for the vast majority of people. Neither omega-6 nor omega-3 polyunsaturated fats lead to the same results. Omega-3 fats do reduce triglycerides, and increase HDL somewhat, but their effect on HDL pales in comparison with that of saturated fats. Excessive consumption of omega-6 fats is associated with chronic inflammation and related health problems.

- With the exception of cases involving familial hypercholesterolemia, there is no conclusive evidence that LDL cholesterol levels are associated with heart disease. Two widely used online calculators of risk of heart disease, based on the Framingham Heart Study and the Reynold Risk Score, do not even ask for LDL cholesterol levels to estimate risk. And that is not because they calculate LDL cholesterol based on other figures; they do not ask for VLDL cholesterol or triglycerides either.

After reading the BBC article again, it is clear that they are re-stating, in general terms, Rudolph Virchow’s mid-1800s lipid hypothesis. And they do so as if it was big news!

11 comments:

ET said...

The focus on LDL alone is startling. Two years ago, after my older brother had his second heart attack, I went to a cardiologist and went through a battery of tests (nuclear stress test, EBCT, etc.) At that time my HDL was 42 and my total was 97! My cardiologist was thrilled. Five months later, I saw him again and through diet changes alone, my HDL rose to 62. However, we was very insistent that I go back on a statin because my LDL was elevated at 80! I pointed out to him that's there's never been any proof that lowering LDL reduces heart disease (thank you ezetimibe!) When I pointed out that my HDL had increased almost 50%, he shrugged it off.

I now understand his indifference to that information. He has no frame of reference for an increase of that magnitude. He advice to his patients at worst, drastically reduces HDL and at best, keeps it the same.

My GP on the other hand was intrigued. My HDL had been as low as 32 and she asked me how I had gotten it so high. I explained that I now restricted carbs and polyunsaturated fats, and dramatically increased my saturated fat intake. She didn't even blink as I explained this to her.

My wife is also coming around, and when I get another EBCT this year, she may become convinced this way of eating is working for me.

Ned Kock said...

Hi ET.

What a contrast between the reaction of the GP and the cardiologist!

There is a whole lot more about HDL that is worth posting. For example, elevated HDL seems to be associated with significantly reduced risk of dementia. Maybe they are a marker for something else; maybe they cause this reduction in risk.

Of the measures we usually get in standard lipid panels, it seems to me that HDL cholesterol levels are the most useful. The fictitious (i.e., calculated) LDL becomes close to worthless for people like you, me and others who ditched refined carbs, sugars, and ultra high omega-6 vegetable oils from their diets.

This is true, in my opinion, even though HDL cholesterol levels are rough measures. HDL particles occur in various subtype patterns, and have a number of functions other than removing cholesterol from atheromas.

Helen said...

Both the BBC and you misattributed the study to the Harvard Medical School. It was by the Harvard School of Public Health. Although I've seen questionable stuff come from the former (for instance, their newsletter), it may be that research standards are not as rigorous at the latter.

Helen said...

Another comment:

I think the "big news" from the study is that, unlike hypotheses about the effects of polyunsaturated fats based solely on the fact that they reduce LDL, this one claimed to show an actual decrease in CHD events - the proof in the pudding.

I think Stephan demonstrated that, due to the lacking quality of several of the studies they used in their analysis, there is no proof in this pudding.
I don't buy it, and I think Stephan

Ned Kock said...

Hi Helen.

Indeed, both the first and last authors of the article are listed as affiliated with the Harvard School of Public Health, even though the first author is also listed as affiliated with the Harvard Medical School.

I corrected the post by just referring to Harvard. Thanks.

I also added a post a few days ago that addresses the study itself, more specifically some of the stats in it:

http://healthcorrelator.blogspot.com/2010/03/more-on-harvard-study-on-saturated.html

Helen said...

Okay - thanks. The article I read on Science Daily only mentioned Harvard School of Public Health. Guess it always pays to look at the original study, though I often don't have enough time and/or interest.

John said...

I'm wondering if I should discontinue Zetia (ezetimibe). I'm taking 30 mg Zetia and 10 mg Lipitor for high cholesterol. But my latest efforts to get fit and cut my weight may have made either or both of these unnecessary.

I started a fairly conventional diet and exercise program in Nov. 2009. The diet was fairly high carb, moderate protein, moderate fat. At around the first week of Apr. 2010 I learned about the Evolutionary Fitness ideas (EF) and changed both diet and exercises to EF style: eliminated most grains and potatoes, cut back on milk and milk products, and did less frequent but more intense exercise (weekly Body by Science big 5 in gym and hard sprinting) along with a lot of relaxed walking.

Some numbers

12/14/2009
weight 235 male height 6'1" age 64
total chol 120
HDL chol 48
LDL chol (calc) 46
VLDL chol (calc) 26
triglicerides 130
A1C 6.4

4/6/2010
weight 215
total chol 123
HDL chol 59
LDL chol (calc) 49
VLDL chol (calc) 15
triglicerides 77
A1C 6.0

With my HDL up to nearly the 60 level discussed earlier in the thread and triglycerides halved, maybe it is about time to experiment with cutting back on the meds. LDL was up an insignificant amount, but VLDL way down. This large improvement was all BEFORE transition to EF diet. I guess I'll stick to EF until my next scheduled physical in July and if the number are as good or better have a conversation with the doctor about whether Zetia still makes any sense for me. I'm looking forward to seeing the effect of 3 months of EF on the numbers.

Ned Kock said...

Hi John.

Let me first point out that I am not a medical doctor.

Having said that, I think your HDL and trigs improved a lot, and those improvements are commonly seen in folks who adopt a diet with little to no foods rich in refined carbs or sugars.

Your LDL and total cholesterol numbers look dangerously low to me, especially with your current HDL. I suggest you take a look at the posts below, and discuss them with your doctor. Your doctor should be able to explain the need for cholesterol drugs in light of these posts.

http://healthcorrelator.blogspot.com/2009/12/total-cholesterol-and-cardiovascular.html

http://healthcorrelator.blogspot.com/2010/04/low-fasting-triglycerides-marker-for.html

http://healthcorrelator.blogspot.com/2010/02/what-should-be-my-hdl-cholesterol.html

Also, take a look at this excellent site:

http://www.cholesterol-and-health.com

Ned Kock said...

Hi John, again:

One more thing. You said that the improvs happened before your diet change. Nevertheless, you lost quite a lot of weight.

That may have made a world of difference, due to its effects on a hormone called adiponectin:

http://healthcorrelator.blogspot.com/2010/03/adiponectin-supplementation-body-fat.html

HDL is in part of health marker. Health generally improves with body fat loss, which I assume is what happened in your case. So, that may be the reason why HDL increased.

Again, your LDL and total cholesterol levels are on the low end of the scale. If they were naturally low, that would be one thing, but if drugs are keeping them low artificially, that is another. You doctor must have a very good reasons to keep you taking the drugs; and it is the doctor's job to explain those reasons to you.

buy viagra without prescription said...

Fascinating article, I staring to gain some weight in the last couple of months, so I'm looking for reasons, causes and solutions.

Rachel Page said...

Great article. Conventional wisdom on dietary fats has changed.