Mon, Jun-22-09, 16:05
Plan: Paleo 99.5%
Location: San Diego, CA
Why did your LDL go up on Low Carb?
Mods, could you sticky this one? It's asked so frequently I think it'd be worth having it readily available.
A few doctors, extremely few unfortunately, understand the problem.
For reasons we donít need to go into here, LDL is fairly difficult (as compared to total cholesterol and HDL) to measure. It can be done, but itís expensive. So instead of measuring it directly, most labs calculate it based on an equation derived by William Friedewald and others in 1972.
Friedewald realized that it was pretty simple to measure total cholesterol, HDL-cholesterol and triglycerides. He knew that total cholesterol was the sum of all the various subfractions of cholesterol, which can be presented by the following equation:
Total cholesterol = HDL-cholesterol + LDL-cholesterol + VLDL-cholesterol
Rearranging this equation to solve for LDL gives us this one.
LDL = Total cholesterol - HLD - VLDL
Friedewald knew that it was easy to measure total cholesterol and HDL but difficult to measure the others. His insight was that the triglyceride level if divided by five could give a close approximation of VLDL. In running his experiments he also realized that this relationship held only if triglyceride levels were 400 mg/dl or under. If they were over this, all bets were off.
So, Friedewald substituted triglycerides (TGL) divided by 5 for VLDL in the above equations, giving us the so-called Friedewald equation for calculating LDL.
LDL = Total cholesterol - HDL - TGL/5
And this is how it is still done in labs all over the world 27 years after Friedewaldís paper. If youíve had a lab report showing an LDL figure, I can guarantee it was calculated by the Freidewald equation and not measured directly.
Whatís wrong with this if it works? Nothing. If it works. Problem is, it doesnít always work. Friedewald himself found that in subjects with triglyceride levels greater than 400 mg/dl the equation didnít hold. Anyone reading this who has had a lipid test showing triglycerides greater than 400 will have note on their lab report saying that LDL couldnít be calculated because triglycerides were too high.
Iíve always thought the same held true for triglycerides under 100 mg/dl, which would apply to almost everyone who sticks to a low-carb diet for any length of time. Triglyceride levels of 40-90 mg/dl are not uncommon, and are, in fact, typical. When Friedewald did his work, the triglyceride levels were mainly up in the 150 Ė 250 mg/dl range, and in this range his equations match pretty well to directly measured LDL levels, but all bets are off with triglycerides above 400 mg/dl and, I suspect, triglyceride levels below 100 mg/dl. MD and I did find this ourselves in a few patients that we did direct LDL measurements on in our practice.
Dr. Davis, a cardiologist, has written extensively about how unreliable the calculation is for people with low triglycerides.
To sum up. If you have triglycerides under 100 the Friedewald calculation used in every "standard" cholesterol test is going to be messed up. You need to have your cholesterol directly counted, which can be done with an NMR or VAP cholesterol test. You might be able to get your doctor to order one, or you can order it yourself but they are rather pricey.
So stop panicking and flush those statins down the toilet, or better yet turn them over to the hazardous waste management service in your area, and keep doing what you're doing.
Last edited by Kristine : Fri, Jul-15-16 at 07:36.
Reason: Fixing links to Dr Davis' blog