Nutrition 2a: Fats and the lipid hypothesis

As part of my personal training course, I took a module in nutrition.  This series is about the various topics that we covered on that course and discusses the areas where I agreed and where I disagreed with the course notes.

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My course notes

First, here’s a the basic course notes primer in fats.  What are they?  What functions do they perform in a diet and how much of them should we eat?  My course notes attempt to answer those questions:

• Functions of fat - the functions of fat as as follows:
  • Protection of internal organs
  • Insulation from cold
  • Insulation of nerve cells
  • Uptake of fat-soluble vitamins (A, D, E and K)
  • Energy
  • Growth and repair of the body’s tissues
  • Maintenance of the menstrual function in females
• Recommended intake of fat – dietary intake of fat should be limited to 30% of total daily calorific intake, noting also that levels below 20% have been linked to increased health risk, therefore giving a recommended band of 20 – 30%.
• Recommended intake of saturated fat – only 10% of daily calorific intake should be saturated fat.
• Functions of cholesterol – my course notes list the functions of cholersterol as follows:
  • Component of cell membranes
  • Used in the liver to make bile, used to digest fat
  • Used to make steroid hormones, including testosterone
• Functions of essential fatty acids – my course notes detail the as follows:
  • Control of blood pressure
  • Prevention of blood clots
  • Reduction of inflammation in arthritis and asthma
  • Enhanced oxygen transportation
  • Enhanced immune response
  • Maintenance of cell membranes and protection against ageing
• Heath risk of hydrogenated fats – my course notes detail simply that these are thought to have a high health risk.

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So what’s to talk about?

Well, all of the functions of fats, cholesterol and essential fatty acids sound pretty important to me.  And indeed, my course notes indicate that letting dietary fat levels fall below 20% has been linked to increased health risks.

So why do my course notes think that we should limit fat to less than 30% of total dietary calorific intake and, specifically, dietary saturated fat to less than 10% of total dietary calorific intake?

The lipid hypothesis.

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The lipid hypothesis? What’s that?

Well, the lipid hypothesis is the single theory that has most influenced the way in which international health organisations and governments try to persuade people to eat.  And most people have never heard of it.

Of course, they’ve heard things like “saturated fat causes heart disease” and “fat clogs up your arteries”.  But surely these are statements of scientific fact?  Buzz, wrong answer.  They are statements based on the assumption that the lipid hypothesis is correct.

Amazing, really.  I mean, even the most ardent evolutionary biologist still refers to “the theory of evolution”.  But, apparently, the lipid hypothesis is beyond the reach of any further scientific investigations.  It is set in stone, a fact for future generations.

The Wikipedia entry reads as follows: “The lipid hypothesis proposes a connection between plasma cholesterol level and the development of coronary heart disease… An accumulation of evidence has led to the acceptance of the lipid hypothesis as scientific fact by the medical community.  However, a small but vocal minority contend that it has not yet been properly validated, and that vascular inflammatory mechanisms prevail independent of blood cholesterol levels.”

Put into simpler terms, the lipid hypothesis is simply the idea that the consumption of dietary saturated fat is responsible for atherosclerosis, which is the furring of the arteries with cholesterol deposits, which in turn can lead to increased blood pressure, heart attacks or strokes.

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And what’s so contentious about that?

What, you mean apart from the positively V for Vendetta style obsession with turning a theory into indisputable fact?

Well, let’s see:

• Diets that are high in saturated fat do not necessarily lead to high blood cholesterol levels (see this article in the Journal of Nutrition)
• Diets that are high in fat decrease the incidence of strokes (see this article in PubMed)
• Low fat diets do not decrease the risk of coronary heart disease (see this article from the European Heart Journal)
• Diets that are high in cholesterol actually reduce the risk of atherosclerosis (see this article in PubMed)
• High cholesterol helps you live longer (see this article in PubMed)
• And low cholesterol means you die earlier (see this article in PubMed)
• Low cholesterol is associated with heart failure (see this article in PubMed)
• Scientists working in this area have a number of criticisms of the approach taken by the proponents of the lipid hypothesis (see this article in PubMed)
• Scientists working in this area are starting to get angry that their research is being ignored (see this article in PubMed) 

I guess you could say that, not only is the lipid hypothesis most definitely a hypothesis, it’s a pretty shaky hypothesis at best…

(Thanks to Healthy Diets and Science for the links)

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So what’s your point of view?

Well, I can see why people like the lipid hypothesis.  After all, fat eaten goes to fat in the arteries, right?  The trouble is, the research doesn’t support it any more.

So I guess I lean towards the viewpoint of that small but vocal minority.  I hope you see enough in the following video to at least question the idea that cholesterol is bad for you…

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See you at the same time next week for more argumentative discussion about nutrition… I’ve gathered a whole selection of “vocal minority scientists” together for an epic links post on this subject.