How do we do it?: LDL cholesterol is measured indirectly using the Friedewald Equation.
The Friedewald Equation:
Where LDL is low-density lipoprotein, TC is total cholesterol, HDL is high-density lipoprotein, and T is triglycerides measured in mg/dl. (1)
We use this equation because measuring LDL directly is difficult so unless deemed necessary or if your willing to pay; your standard lipid profile uses the equation.
Friedewald states that the formula is inaccurate for patients with triglycerides over 400mg/100ml (1)
But upon looking at his data set the majority (~75%) of the patients had triglycerides over 100 which makes me wonder if the formula is incorrect when triglycerides get very low (50-70), as suggested in study 2. This is important because many people who enbark on a high fat diet see their LDL go up and despite everything else getting better (triglycerides are down, HDL is up, body composition is better, etc...) they (or their doctor) pick this one thing out and proceed to freak out.
Doctor Reviewing High-Fat Diet Patient's Blood Results:
Patient sitting waiting for doctor to come in. Looks at watch. Doctor enters.
Doctor: "Sorry about the wait I was busy reading the ADA's website so I can stay up to date with the best, most current, unbiased data."
Patient: "That's alright... Did you look at my blood results?"
Doctor: "Yes I did and I must say that it all looks good, your HDL, triglycerides, thyroid, and general chemistry are absolutely perfect. The only problem is your LDL cholesterol."
Patient: "What's wrong with it?"
Doctor: "Well it's just slightly higher then I'd like to see it."
Patient: "Well since the LDL was measured indirectly, couldn't all the LDL be the harmless large and puffy ones? Shouldn't I have a direct test and have the prominent type of LDL determined before worrying?"
Doctor: "Hmmmm... Well I... uhhh... Let's just see if we can get it down. Tell me, what do you eat in a typical day?"
Patient: "Well I usually have six over easy eggs and 1/2lb of grass fed beef for breakfast, then I have 1lb of grass-fed beef, or free-range chicken, or lamb for dinner along with a heaping of lightly steamed leafy greens. Oh and all my eggs and meat are cooked in coconut oil." [this is my typical daily diet]
Doctor: "YOU ARE GOING TO DIE TOMORROW FROM CORONARY HEART DISEASE! DON'T YOU KNOW THAT SATURATED FAT WILL CLOG YOUR ARTERIES? IT'S A MIRACLE YOU TOLD ME BEFORE YOU ATE THIS DIET LONG TERM!"
Patient: "I've been eating this way for 5 years"
Doctor: "Well if want to live past 50 you'll throw out that diet and follow a 10% fat diet with all fat coming from vegetable sources, eat lots of fruit, veggies, and whole grains and no meat except fish."
Patient: "What happened to the LDL only be slightly elevated and not that big of a deal?"
Doctor: "That was before I knew you were eating a diet designed to kill you. Tell me are you suicidal? There is a good psychologist upstairs that I want you to see because no one in their right mind would eat this way"
Case in point: Don't flip if LDL goes up on a high-fat (especially high saturated) diet, look at you HDL and triglycerides. If you are still concerned get you LDL directly tested and have the lab determine the type of LDL that is most prominent. (full post on the LDL types coming soon)
1) Estimation of the Concentration of Low-Density Lipoprotein Cholesterol in Plasma,Without Use of the Preparative Ultracentrifuge
2) The Impact of Low Serum Triglyceride on LDL-Cholesterol Estimation