Cholesterol Explained: LDL, HDL, Triglycerides, and What Actually Matters

Cholesterol is one of the most misunderstood topics in nutrition. Patients are told their "bad cholesterol is high" and walk away with a statin prescription, never quite understanding what the numbers mean or what they can do beyond medication. This guide unpacks the science, what cholesterol actually is, what each part of a lipid panel measures, which numbers matter most, and how lifestyle and medication move them. The 2018 ACC/AHA cholesterol guidelines and the 2022 update form the backbone of the recommendations here.

What cholesterol actually is

Cholesterol is a waxy, fat-like substance that every cell in your body needs. It is a structural component of cell membranes, a precursor for steroid hormones (cortisol, estrogen, testosterone), and the backbone of bile acids that digest fat. Your liver produces about 1,000 mg of cholesterol per day, far more than the 300 mg per day in a typical diet. This is why dietary cholesterol has a relatively small effect on blood cholesterol for most people. The body tightly regulates total cholesterol by adjusting liver production based on dietary intake.

Because cholesterol is fat-soluble and blood is water-based, cholesterol cannot travel alone. It is packaged into lipoproteins, tiny spheres with a fat-rich core and a water-soluble outer shell. These lipoproteins come in several varieties based on density: chylomicrons (lowest density, carry dietary fat from the gut), VLDL (very-low-density, carries liver-made triglycerides), IDL (intermediate), LDL (low-density, the main cholesterol carrier), and HDL (high-density, the "reverse transport" particle that carries cholesterol back to the liver for disposal).

LDL, the primary driver of atherosclerosis

Low-density lipoprotein (LDL) is the primary driver of atherosclerotic plaque formation. LDL particles cross the artery wall, get oxidized, and trigger an inflammatory cascade that produces the foam cells and plaque that narrow arteries. The relationship between LDL and cardiovascular risk is log-linear: each 1 mmol/L (39 mg/dL) reduction in LDL reduces cardiovascular events by about 22%, and this holds true across statins, ezetimibe, and PCSK9 inhibitors, suggesting the LDL itself (not just the drug) is causal.

The 2018 ACC/AHA guidelines set LDL targets based on cardiovascular risk:

• Low risk: No specific target; treat if LDL ≥190 mg/dL
• Moderate risk: Consider statin if LDL ≥130, especially with risk-enhancing factors
• High risk (ASCVD, diabetes with risk factors, etc.): Target <70 mg/dL
• Very high risk (recurrent events, polyvascular disease): Target <55 mg/dL

Each LDL measurement has limitations. Friedewald-calculated LDL (the standard method) becomes inaccurate when triglycerides are above 200 mg/dL; in that case, a direct LDL or LDL particle number (LDL-P) test is more reliable. Some clinicians now prefer apolipoprotein B (ApoB), which counts every atherogenic particle, but insurance coverage is inconsistent.

HDL, protective but complicated

HDL is the "reverse cholesterol transport" particle. It removes cholesterol from peripheral tissues (including artery walls) and carries it back to the liver for disposal. Population studies consistently show that higher HDL is associated with lower cardiovascular risk. The target is ≥40 mg/dL in men and ≥50 mg/dL in women. Aerobic exercise (150 min/week), omega-3 fatty acids, modest alcohol, and quitting smoking all raise HDL by 3-10 mg/dL.

But HDL is more complicated than "higher is always better." Genetic conditions that produce very high HDL (e.g. CETP deficiency) do not always protect against cardiovascular disease, and several drug classes that raised HDL (niacin, CETP inhibitors) failed to reduce events in clinical trials. The current view is that HDL function, its ability to perform reverse cholesterol transport, matters more than HDL concentration. Unfortunately, HDL function tests are not yet routinely available.

Triglycerides, the marker of metabolic health

Triglycerides are the main storage form of fat in the body and the main fat type in the bloodstream after meals. Fasting triglycerides below 150 mg/dL are normal; 150-199 borderline; 200-499 high; ≥500 very high (and a pancreatitis risk). High triglycerides are driven by:

• Refined carbohydrate and sugar (especially fructose)
• Alcohol
• Sedentary lifestyle
• Insulin resistance and type 2 diabetes
• Hypothyroidism and kidney disease
• Genetic hypertriglyceridemia (rare)

Lowering triglycerides is one of the most rewarding dietary interventions. Cutting added sugar and alcohol, increasing omega-3 (2-4 g/day EPA+DHA), and 150 min/week of aerobic exercise can drop triglycerides 30-50% in 8-12 weeks. The triglyceride-to-HDL ratio is a free proxy for insulin resistance: a ratio below 2 typically indicates insulin sensitivity, while above 3 suggests insulin resistance.

Non-HDL cholesterol, the underappreciated workhorse

Non-HDL cholesterol (total minus HDL) captures every atherogenic particle: LDL, VLDL, IDL, and lipoprotein(a). The 2018 guidelines set non-HDL targets 30 mg/dL above the LDL target (so <130 mg/dL for higher-risk patients). Non-HDL is especially useful when triglycerides are high (>200 mg/dL) because Friedewald-calculated LDL becomes unreliable in that setting. The non-HDL test is essentially free, it's already on every standard lipid panel, and many cardiologists now consider it the single best single-marker predictor of cardiovascular risk.

Lipoprotein(a), the genetic wildcard

Lipoprotein(a), or Lp(a), is an LDL variant with an attached apolipoprotein(a) that promotes clotting and inflammation. Elevated Lp(a), affecting roughly 20% of people, increases cardiovascular risk 2-4× independently of other lipids. Lp(a) is almost entirely genetically determined: lifestyle and statins do not lower it meaningfully. (PCSK9 inhibitors and a new class of antisense oligonucleotides do.) Because standard lipid panels do not measure Lp(a), the European Atherosclerosis Society and many U.S. lipid experts now recommend a one-time Lp(a) test in every adult's lifetime. If yours is high (>50 mg/dL), it shifts your cardiovascular risk calculation meaningfully.

Lifestyle levers that actually move cholesterol

Lower LDL

• Reduce saturated fat to under 10% of calories (under 7% for high-risk). Replacing saturated with unsaturated fat lowers LDL 10-15%.
• Add soluble fiber. Oats, beans, psyllium, apples, flaxseed. 5-10 g/day lowers LDL 5-10 mg/dL.
• Plant sterols/stanols. 2 g/day lowers LDL 8-10%. Available in fortified foods or supplements.
• Replace butter with olive oil. Each tablespoon swap saves ~7 g saturated fat.
• Lose weight if overweight, 5-10% loss lowers LDL 5-10 mg/dL.

Raise HDL

• Aerobic exercise. 150 min/week raises HDL 3-6 mg/dL.
• Omega-3 from fish or supplements raises HDL 1-3 mg/dL.
• Quit smoking, raises HDL 4-8 mg/dL within months.
• Moderate alcohol raises HDL but is not a reason to start drinking.

Lower triglycerides

• Cut added sugar and refined carb. Biggest single lever.
• Reduce alcohol, even small amounts can spike triglycerides in sensitive individuals.
• Omega-3 EPA+DHA 2-4 g/day. Lowers TG 20-50%.
• Aerobic exercise. 150 min/week lowers TG 15-25%.
• Weight loss if overweight.

Medication, when lifestyle is not enough

Statins remain the cornerstone of cholesterol management. They lower LDL 30-60% and reduce cardiovascular events by ~25% per 1 mmol/L LDL reduction. They are recommended for most adults with established ASCVD, LDL ≥190 mg/dL, diabetes with additional risk factors, or 10-year ASCVD risk ≥7.5%. Ezetimibe adds another 15-20% LDL reduction when statins alone are insufficient. PCSK9 inhibitors (evolocumab, alirocumab) add another 50-60% and dramatically reduce events in high-risk patients, but at high cost. Bempedoic acid is a newer option for statin-intolerant patients.

For elevated triglycerides, icosapent ethyl (a purified EPA) at 4 g/day reduced cardiovascular events 25% in the REDUCE-IT trial, a landmark result that established prescription omega-3 as a cardiovascular drug, not just a supplement. Standard fish oil supplements at lower doses have not shown the same benefit. Fibrates (fenofibrate, gemfibrozil) are reserved for very high triglycerides (≥500) to prevent pancreatitis.

Practical screening schedule

• Adults 20-75 with no risk factors: Lipid panel every 4-6 years
• Adults with risk factors (family history, BP, diabetes, smoking): Annually
• Adults 40-75: Calculate 10-year ASCVD risk to guide statin decision
• Adults on statins: Lipid panel 4-12 weeks after starting or changing dose, then annually
• One-time Lp(a) test in every adult at least once
• Coronary artery calcium (CAC) score for borderline ASCVD risk (5-20%) to refine statin decision

Use our Cholesterol Ratio Calculator and Cardiovascular Risk Calculator to interpret your numbers, and our Heart Health goal page to organize your prevention plan.