LDL Cholesterol: What It Is, What It Is Not, and Why One Number Tells You Nothing
Your doctor circles a number on your lab results and calls it your bad cholesterol. You leave the appointment with a prescription or a warning. What you probably did not receive is an explanation of what that number actually measures, what drives it up or down, and whether it tells you anything meaningful about your heart.
It is worth starting at the beginning.
LDL is not cholesterol
LDL stands for low-density lipoprotein. It is a particle, not a molecule. Its job is to transport cholesterol through the bloodstream, because cholesterol cannot travel on its own. HDL, high-density lipoprotein, does the same job in the other direction, carrying cholesterol back to the liver.
There is only one cholesterol molecule. It is the same molecule whether it is riding inside an LDL particle or an HDL particle. Calling LDL "bad cholesterol" is like calling a delivery truck bad cargo. The truck and its contents are two different things.
Dr. Paul Mason, a physician whose work on lipids, insulin resistance, and metabolic health has become essential viewing for anyone trying to understand their bloodwork, makes this point clearly and repeatedly. LDL-C, the number on your lab report, measures the amount of cholesterol carried inside LDL particles. It does not tell you how many particles there are, how large or small they are, or how they are behaving in your arteries.
Why particle size matters more than the number
Not all LDL particles are the same. Large, buoyant LDL particles are now understood to carry very little cardiovascular risk. Small, dense LDL particles are the ones associated with atherosclerosis. They are small enough to penetrate the artery wall, they oxidize more easily, and they are more likely to accumulate in tissue.
Here is the critical point. Small, dense LDL is produced in response to high triglycerides and insulin resistance. It is a downstream consequence of eating too many refined carbohydrates and processed sugars. Large, buoyant LDL, the kind that tends to rise on a ketogenic diet, is produced in a metabolically healthy environment and behaves very differently.
Your standard LDL-C number does not distinguish between them. Two people can have the same LDL-C with completely different particle profiles and completely different levels of cardiovascular risk.
The ratio that actually tells you something
Dr. Ken Berry, a family physician and author of Lies My Doctor Told Me, points to the triglyceride to HDL ratio as one of the most informative and underused markers in standard bloodwork. The math is simple. Divide your triglyceride number by your HDL number.
A ratio below 1.5 is optimal. It reflects low insulin resistance, a pattern of large buoyant LDL, and a metabolic environment with low cardiovascular risk. A ratio between 1.5 and 3.5 is worth monitoring. A ratio above 3.5 signals insulin resistance, a shift toward small dense LDL particles, and a metabolic pattern that does correlate with cardiovascular disease.
This ratio costs nothing to calculate. It uses numbers already on your standard lipid panel. And it reflects the actual metabolic conditions driving risk far better than LDL-C alone ever could.
What the hospital data shows
A review of more than 136,000 patients hospitalized with coronary artery disease found that nearly half had LDL-C below 100 mg/dL on admission. Nearly 18 percent had LDL below 70 mg/dL. These are numbers most doctors would consider excellent. What the majority of these patients did share was low HDL, a direct marker of insulin resistance and metabolic dysfunction.
High LDL did not protect them. Low LDL did not protect them either. The metabolic environment did the damage, and LDL-C did not predict it.
How to find out what is actually happening in your arteries
If you want to know whether you have cardiovascular disease, the most direct way to find out is a coronary artery calcium scan, or CAC scan. This imaging test measures calcification in your coronary arteries. It tells you whether atherosclerosis is present. It does not infer risk from a surrogate marker. It shows you what is there.
Research published in the journal Atherosclerosis concludes that direct assessment of atherosclerosis is more predictive of cardiovascular risk than traditional markers including blood cholesterol levels, and that the CAC scan is superior to any other available risk assessment tool.
A CAC score of zero means the likelihood of coronary artery disease is extremely low, regardless of your LDL number. The test costs less than $200 in most of the United States. If your doctor is concerned about your cholesterol and you want a real answer, this is the test to ask for.
What this means for how you read your next lab result
Your LDL-C number is one data point. On its own it tells you almost nothing about your actual cardiovascular risk. Pair it with your triglyceride to HDL ratio. Ask your doctor about particle size testing if it is available. Consider a CAC scan if you want to know your actual arterial health.
And if you are eating low-carb, your triglycerides are down, your HDL is up, your blood sugar has improved, and your LDL rose, understand what that pattern means. It does not mean your diet is harming you. It means your metabolism is changing, and the changes that matter most are moving in the right direction.
Disclaimer: This article is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before making changes to your diet, lifestyle, or treatment plan.
References:
Volek JS, Fernandez ML, Feinman RD, Phinney SD. Dietary carbohydrate restriction induces a unique metabolic state positively affecting atherogenic dyslipidemia, fatty acid partitioning, and metabolic syndrome. Prog Lipid Res. 2008 Sep;47(5):307-18.
Sachdeva A, Cannon CP, Deedwania PC, et al. Lipid levels in patients hospitalized with coronary artery disease: an analysis of 136,905 hospitalizations. Am Heart J. 2009 Jan;157(1):111-117.e2.
da Luz PL, Favarato D, Faria-Neto JR Jr, Lemos P, Chagas AC. High ratio of triglycerides to HDL-cholesterol predicts extensive coronary disease. Clinics (Sao Paulo). 2008 Aug;63(4):427-32.
Raggi P. Coronary calcium is all we need for risk assessment, yet we do not use it often enough. Atherosclerosis. 2019 Mar;282:167-168.
Mortensen MB, Caínzos-Achirica M, Steffensen FH, et al. Association of Coronary Plaque With Low-Density Lipoprotein Cholesterol Levels and Rates of Cardiovascular Disease Events Among Symptomatic Adults. JAMA Netw Open. 2022 Feb 1;5(2):e2148139.
Diamond DM, Bikman BT, Mason P. Statin therapy is not warranted for a person with high LDL-cholesterol on a low-carbohydrate diet. Curr Opin Endocrinol Diabetes Obes. 2022 Oct 1;29(5):497-511.
Hyde PN, Sapper TN, Crabtree CD, et al. Dietary carbohydrate restriction improves metabolic syndrome independent of weight loss. JCI Insight. 2019 Jun 20;4(12):e128308.
