Saturday, September 3, 2011

Medicine's War on Dietary Fat: How America Got Fat

     The story of how dietary fat was pathologized and became the focus of US public health policy is a story about what happens when public demand for simple advice collides with the confusing ambiguity of real science.  Ancel Keys, an enormously influential american scientist who studied the effect of dietary fats on health (same fellow developed mobile meals for the armed forces in the 1940s - "K Rations") almost single-handedly convinced the american medical establishment of the need to decrease our fat intake. Where did this idea come from and why did it get such traction?

     In the 1950's the US appeared to experience the start of a dramatic increase in coronary heart disease. Keys published  his seminal "Seven Countries Study" in this context, demonstrating that serum cholesterol was strongly correlated with cardiovascular illness.  He suggested that dietary fat was the culprit, causing an increase in cholesterol which in turn triggered heart disease. This causal chain was not accepted by many in the medical community who cited flaws in the methodology of his study. But the skeptical camp was eclipsed by the politically adept Keys. By1982 the Keys ideology held sway and the US Department of Agriculture, the American Medical Association, and the American Heart Association told an increasingly health-conscious public that fat consumption had to be reduced. Americans were flooded with food products pumped up with carbohydrates to replace the fat and marketed as heart healthy foods. Unfortunately this well intentioned intervention not only stood on false assumptions, it initiated the obesity epidemic.

     Einstein once said "Not everything that can be counted counts, and not everything that counts can be counted."  It turns out, this applies to cholesterol. Not all LDL cholesterol is created equal. In fact, LDL can be divided into two (or four) camps according to size and buoyancy. Large buoyant LDL do not cause disease and usually coexist with low triglycerides and high HDL levels. This profile is known as Pattern A. On the other hand, small dense LDL are usually found with high triglycerides and low HDL. This B Pattern does form plaques in coronary arteries and causes heart disease.

     Now for the kicker. Dietary fat generally increases large buoyant (benign) LDL. Dietary carbohydrate increases small dense LDL! In other words, the mantra dietary fat is causing heart disease and obesity is a myth.  And when your doctor gives you an LDL cholesterol reading, you don't know what it means. You need to know how much of what type of LDL (the test is available at Quest).  This is not to suggest you go on a saturated fat binge, but let's take a look at what the data tells us.

  • Reducing fat and increasing carbs (especially refined carbs) leads to weight gain and a metabolic state that favors a worsening of atherosclerotic heart disease
  • Reducing carbohydrate, but not saturated fat, improves the disordered blood fat condition
  • Despite conventional wisdom that reducing all saturated fat is beneficial for cardiovascular health the evidence is lacking
  • In the Seven Countries Study the regions with the highest coronary heart disease (Finland) and the lowest (Crete) had the same amount of total fat intake, about 40%, the highest amongst the 16 populatios (yes 16, Keys only included 7!)
  • While there is no question that trans fats are associated with increased heart disease, total fat is not

     So over the past 3 decades, while fat consumption has steadily decreased, the prevalence of obesity and type two diabetes has skyrocketed and cholesterol-lowering medications have become a multibillion dollar per year enterprise.

     In the next blog I will discuss statins, those cholesterol lowering medications, and why they may be really good for you. It has nothing to do with cholesterol!


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