Triglycerides

What is TG?

Triglycerides are the main form in which the body stores and transports fat: three fatty acids attached to a glycerol backbone. In blood they travel inside triglyceride-rich lipoproteins — chylomicrons, which the intestine assembles after a meal, and VLDL, which the liver exports around the clock. The laboratory value is the total triglyceride mass across all particles, which is why it swings far more with meals, alcohol and the events of the past few days than cholesterol does.

What is TG made of, and where does it come from?

In a fasting sample almost all triglyceride sits in VLDL, with small amounts in LDL and HDL; after a meal chylomicrons join the pool and can dominate it for several hours. The assay hydrolyses triglyceride to glycerol and measures the glycerol, so free glycerol already in the sample — raised by hard exercise, stress or certain intravenous fluids — is counted as triglyceride unless the method corrects for it.

What does TG do in the body?

Triglycerides deliver fatty acids to muscle for fuel and to adipose tissue for storage; lipoprotein lipase on capillary walls, switched on by insulin, strips the fatty acids from passing particles. When insulin action is impaired the whole system backs up: adipose tissue releases more fatty acids to the liver, the liver exports more VLDL, clearance slows, and triglycerides rise while HDL-C falls and LDL shifts toward small dense particles. Genetic and cohort evidence reviewed by Nordestgaard and Varbo (Lancet 2014) indicates that the cholesterol in triglyceride-rich remnant particles contributes causally to atherosclerosis rather than merely marking it, because remnants enter the artery wall much as LDL does. Very high triglycerides carry a second, separate hazard — acute pancreatitis — which becomes a real concern above roughly 10 mmol/L (885 mg/dL).

What does a high TG mean?

Raised triglycerides most often signal insulin resistance — excess visceral fat, a diet high in refined carbohydrate and alcohol, physical inactivity, or type 2 diabetes — and are read together with HDL-C, waist circumference and glucose rather than alone. The 2018 AHA/ACC guideline treats persistently raised fasting triglycerides of 1.7 mmol/L (150 mg/dL) or more as a risk-enhancing factor; the 2011 AHA scientific statement classes 2.3-5.6 mmol/L (200-499 mg/dL) as high and 5.6 mmol/L (500 mg/dL) or more as very high, the range where preventing pancreatitis becomes the first priority. A single elevated result carries limited weight, because triglycerides vary more from day to day than any other lipid; a repeat under standard conditions is the usual first step.

Common causes:

• Overweight with excess visceral fat, insulin resistance, prediabetes or type 2 diabetes — the most common cause by far.
• A diet high in refined carbohydrate and sugar, particularly fructose from sugar-sweetened drinks, which the liver converts directly into triglyceride.
• Alcohol, which increases hepatic triglyceride synthesis and slows clearance; the effect is dose-dependent and exaggerated in people who are already prone.
• Medications including oral oestrogens, isotretinoin, corticosteroids, thiazide diuretics, non-selective beta-blockers, some antipsychotics, tamoxifen and some antiretrovirals.
• Hypothyroidism, chronic kidney disease, nephrotic syndrome and pregnancy.
• Inherited disorders — familial hypertriglyceridaemia, familial combined hyperlipidaemia, and rare lipoprotein lipase deficiency, in which values can exceed 10 mmol/L from childhood.

What does a low TG mean?

A low triglyceride value is almost always unimportant and usually reflects a lean, insulin-sensitive, physically active state or a very low-fat diet. The rare exceptions are unexplained low values, especially when total cholesterol is low at the same time: malabsorption from coeliac disease or pancreatic insufficiency, malnutrition, hyperthyroidism, and rare inherited disorders of apolipoprotein B such as abetalipoproteinaemia. In those cases the triglyceride value is a bystander pointing at something else, not a problem in itself.

Common causes:

• A lean, active, insulin-sensitive metabolism.
• A very low-fat or low-calorie diet in the preceding days.
• Hyperthyroidism, which speeds lipoprotein clearance.
• Malabsorption or malnutrition.
• Rare inherited disorders of apolipoprotein B.

What moves TG apart from disease?

Fasting state — the largest single factor raises it

Triglycerides rise by around 0.3 mmol/L on average after an ordinary meal and peak at about four hours; a large fatty meal can double the fasting value. The 2016 EAS/EFLM joint statement accepts non-fasting samples for routine lipid testing, but advises a fasting repeat when non-fasting triglycerides exceed 5 mmol/L (440 mg/dL). A result should always be read with its fasting status attached.

Alcohol in the preceding days raises it

A single evening of drinking can raise the next morning's fasting triglycerides noticeably, and a weekend of heavy drinking can push a normally unremarkable value into the high range. The effect is much larger in people with underlying insulin resistance or a genetic tendency.

What was eaten in the previous week either direction

Several days of high carbohydrate or high sugar intake raise fasting triglycerides, and several days of carbohydrate restriction lower them, so the value reflects the recent week as much as the underlying metabolism. A test taken after a holiday, a celebration or a period of unusual eating describes that period, not the baseline.

Exercise in the preceding 24 hours lowers it

A single prolonged bout of exercise lowers triglycerides for the next day or so, by around 20% in controlled studies, through increased lipoprotein lipase activity. A value drawn the morning after an unusually long run or ride understates the usual level.

Ordinary biological variation either direction

Triglycerides have the largest within-person variation of any routine lipid, around 20% even under identical fasting conditions. Two results from the same person can differ by 20-30% by chance alone, which is why guidelines base decisions on the average of repeated measurements rather than a single value.

Pregnancy raises it

Triglycerides rise two- to three-fold by the third trimester as a normal adaptation that supplies the fetus, and return to baseline over the weeks after delivery. A value from late pregnancy cannot be compared with a non-pregnant result.

Which other tests are read together with TG?

VLDL Cholesterol same panel

VLDL is the particle that carries most fasting triglyceride, and VLDL cholesterol is usually estimated directly from the triglyceride value — triglycerides divided by 2.2 in mmol/L, or by 5 in mg/dL. The two numbers are two views of the same particles.

HDL Cholesterol read as a ratio

Triglycerides and HDL-C move in opposite directions through insulin resistance, so the TG/HDL-C ratio is a practical marker of insulin resistance and of small dense LDL. High triglycerides with a low HDL-C is the signature of the metabolic syndrome.

LDL Cholesterol downstream

Most laboratories calculate LDL-C from the other lipids using the Friedewald equation, which breaks down as triglycerides rise and is invalid above about 4.5 mmol/L (400 mg/dL). High triglycerides also shift LDL toward smaller, denser particles that carry more risk per unit of LDL-C.

Glycated Hemoglobin (HbA1c) upstream

Glycaemic control and triglycerides move together through insulin resistance; triglycerides often rise years before HbA1c does, and improving one usually improves the other.

Alanine Aminotransferase downstream

The same surplus of fatty acids that raises triglycerides is stored in the liver as fat. A raised ALT alongside high triglycerides points toward metabolic-dysfunction-associated fatty liver, which shares its causes and its remedies.

Gamma-Glutamyl Transferase can distort it

A raised GGT next to high triglycerides makes alcohol the likely explanation, which changes what the triglyceride value means and what will bring it down.

Which foods affect TG?

• Cutting sugar-sweetened drinks, fruit juice and added sugar, especially fructose — lowers strong evidence
• Reducing alcohol, or stopping it while triglycerides are very high — lowers strong evidence
• Replacing refined carbohydrate with unsaturated fat and whole grains — a Mediterranean pattern — lowers strong evidence
• Oily fish twice a week — salmon, mackerel, sardines — lowers moderate evidence
• Large, high-fat meals late in the evening — raises moderate evidence

Which supplements are studied for TG?

Omega-3 fatty acids (EPA + DHA) strong evidence

Marine omega-3 fatty acids reduce hepatic VLDL production and speed triglyceride clearance, lowering triglycerides by roughly 20-30% at higher intakes; the effect grows with dose and with the starting value. Prescription-strength purified EPA, tested in the REDUCE-IT trial (2019), reduced cardiovascular events in statin-treated people with raised triglycerides, whereas ordinary fish-oil supplements at typical amounts have not shown the same outcome benefit.
Typical dose: 1-2 g/day of combined EPA and DHA
Cautions: Doses that lower triglycerides meaningfully are above ordinary supplement amounts and belong under medical supervision, particularly when triglycerides are very high. Recent trials link higher intakes to a small increase in atrial fibrillation. Can prolong bleeding time; people taking anticoagulants or antiplatelet drugs should check with their doctor first. DHA-containing products can raise LDL-C slightly in people with very high triglycerides.

Niacin (nicotinic acid, high dose) moderate evidence

Pharmacological niacin lowers triglycerides by 20-40% by reducing fatty-acid release from adipose tissue and hepatic VLDL output. The AIM-HIGH and HPS2-THRIVE trials found no cardiovascular benefit from adding it to a statin, and it is now rarely used for this purpose.
Typical dose: no general dose given
Cautions: Effective doses are prescription-level and not appropriate to self-select; amounts found in multivitamins do not lower triglycerides. Raises blood glucose and uric acid, causes flushing, and can injure the liver, especially in sustained-release forms. In HPS2-THRIVE, adding niacin increased serious adverse events without reducing cardiovascular events.

Berberine emerging evidence

Berberine activates AMPK and improves insulin signalling, and small trials report reductions in triglycerides alongside glucose. The trials are short, small and of variable quality, so the size of the effect is uncertain.
Typical dose: no general dose given
Cautions: Inhibits CYP3A4 and P-glycoprotein and can raise blood levels of many prescription drugs — a real interaction risk. Can cause hypoglycaemia when combined with glucose-lowering medication. Contraindicated in pregnancy, breastfeeding and newborns, and should not be started without telling the prescribing doctor.

How does exercise affect TG?

Regular aerobic exercise strong evidence

How much: At least 150 minutes a week at moderate intensity, or 75 minutes vigorous, ideally spread across most days so that the short-lived effect of each session overlaps with the next.
What to expect: Aerobic training lowers fasting triglycerides by around 10-20%, and of all the standard lipids, triglycerides are the one exercise moves most. Much of the effect is acute — each session lowers triglycerides for a day or two — which is why regularity matters more than intensity.

Resistance training moderate evidence

How much: Two or three sessions a week covering the major muscle groups.
What to expect: Resistance training lowers triglycerides modestly on its own and adds to aerobic training through improved insulin sensitivity and preserved muscle during weight loss.

Walking after meals moderate evidence

How much: 10-20 minutes at an easy pace beginning shortly after eating.
What to expect: Light activity after a meal blunts the post-meal triglyceride rise, and post-meal triglycerides predict cardiovascular risk at least as well as fasting values. A small, repeatable intervention with unusually good adherence.

Which lifestyle factors affect TG?

Weight loss where relevant strong evidence

Losing 5-10% of body weight lowers triglycerides by roughly 20%, more than it lowers any other lipid, because it directly reduces the flow of fatty acids from visceral fat to the liver. Triglycerides are the lipid by which a weight-loss effort is most fairly judged.

Alcohol strong evidence

Alcohol is one of the few dietary factors that can raise triglycerides quickly and substantially, and stopping it is often the single largest correctable contributor. The 2011 AHA scientific statement singles out alcohol restriction, especially when triglycerides are very high.

Sleep and shift work emerging evidence

Short sleep and circadian disruption worsen insulin sensitivity within days and are associated with higher triglycerides in shift workers. If triglycerides have drifted up without a change in diet, sleep and working hours are worth examining.

How should you prepare for a TG test?

• When a fasting sample is requested, fast for 9-12 hours with water only; a non-fasting result is acceptable for screening but must be labelled as such.
• Avoid alcohol for at least two to three days before the test, and keep to the usual diet — not a feast and not an unusually strict one.
• Skip unusually long or hard exercise in the 24 hours before the draw; the day-after effect lowers the value.
• Confirm a raised value with a repeat under the same conditions before acting on it. Day-to-day variation alone can move triglycerides by 20-30%.
• Mention pregnancy, recent illness and any new medication — each changes how the result should be read.

References

1. Miller M et al. Triglycerides and cardiovascular disease: a scientific statement from the American Heart Association. Circulation 2011 — https://doi.org/10.1161/CIR.0b013e3182160726
2. Nordestgaard BG, Varbo A. Triglycerides and cardiovascular disease. Lancet 2014 — https://doi.org/10.1016/S0140-6736(14)61177-6
3. Nordestgaard BG et al. Fasting is not routinely required for determination of a lipid profile — joint consensus statement from the EAS and EFLM. Eur Heart J 2016 — https://doi.org/10.1093/eurheartj/ehw152
4. Grundy SM et al. 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA Guideline on the Management of Blood Cholesterol. Circulation 2019 — https://doi.org/10.1161/CIR.0000000000000625
5. Bhatt DL et al. Cardiovascular risk reduction with icosapent ethyl for hypertriglyceridemia (REDUCE-IT). N Engl J Med 2019 — https://doi.org/10.1056/NEJMoa1812792