Weight of the Evidence

Fat, Cholesterol, LDL, HDL Discussion

For decades a diet that is higher in fat than recommended – that is more than 30% of calories from fat and more than 10% from saturated fat – has been implicated as a “cause” of high cholesterol, which in turn has been implicated as a “cause” of cardiovascular disease.

Remember in school the equation problem “A=B, B=C, so A=C?”
When it comes to cholesterol, the equation is fairly simple and straight-forward:

  • More than 30% of calories from fat = risk of high cholesterol
  • High cholesterol = risk of cardiovascular disease
  • More than 30% of calories from fat = risk of cardiovascular disease

But, it is true?

For years research data has continued to find contradictory results when extrapolating data on diet and cholesterol and heart disease. When data supports the idea, the media is all over it…when the findings are weak or in contradiction to the idea, the findings are often ignored, discredited, or some flaw is found in the design to explain the contradiction. Then, there is the “paradox” explanation – namely the “French Paradox” and the “Spanish Paradox” – advanced when nothing else can explain away findings.

New findings, reported today by Reuters Health in the article, “Genes key in how diet affects cholesterol levels” challenge the conventional wisdom of “diet = high cholesterol.”

The study of 28 pairs of male twins — one a lean athletic type, the other a bit rounder and sedentary — found that brothers tended to show the same cholesterol response to high-fat and low-fat diets, even though their exercise habits were starkly different.

Because identical twins share the same genetic makeup, the findings point to the importance of genes in determining how a person’s cholesterol levels respond to diet and lifestyle changes, according to the study authors.
The study followed 28-pairs of identical twins (male) and used cross-over diets containing different amounts of fat. One diet had 40% of calories from fat, the second had 20% of calories from fat.


The study found a high degree of similarity in how brothers’ LDL Cholesterol (the “bad” form of cholesterol) responded to the switch from the high-fat diet to the low-fat one. On average, the men’s LDL declined on the low-fat diet, but any individual’s response seemed to depend largely on genes.

In general, low-fat diets tend to lower LDL concentrations, but can also decrease “good” HDL cholesterol and raise triglycerides, another type of blood fat. So cutting dietary fat may not have a net benefit, depending on the individual.

What the article didn’t state was that some of the twins followed did better with a higher fat diet than a lower fat diet. Add to that the finding that HDL may decrease while triglycerides increase on a low-fat diet – those observations are noteworthy and future research must explore why. HDL is basically the “garbage collector” of cholesterol. The evidence to date supports the contention that high triglycerides are a risk factor. When a dietary change impacts both negatively, this should be a red flag!

For those who fail to better their cholesterol profile with diet, genes — rather than a lack of will — could be the reason, said Paul T. Williams, a researcher at the Lawrence Berkeley National Laboratory in California and the study’s lead author.

Controlled-carb diets have been shown to markedly improve cholesterol levels in people following them in controlled-studies. This is not to say everyone benefited – there is a population whose cholesterol responds negatively to a higher-fat, low-carb diet.

Some studies suggest this population could be as high as 30% of the general population.
For this reason, it is critical that you have your cholesterol profile followed by a physician if you modify your diet to be low-carb or, with these findings that show HDL and triglycerides may be negatively impacted by a low-fat diet if you go that route.

Until, or unless cholesterol levels are ruled out of the equation as a risk factor, it is important to have your cholesterol checked with any dietary change. If you’re not seeing a positive result in your cholesterol profile work with your doctor to adjust your macronutrient intake to see if a different one works better.