Triglycerides are the main type of fat in your blood. Triglyceride is a general term for a type of lipid-containing three fatty acids (tri) bound to a glycerol. Triglycerides are used by the body as energy. They are also stored in fat cells.
Most of the time when you go to the doctor for a lipids test they are worried about higher LDL or lower HDL levels. These are classically linked to cardiovascular disease risk. But triglycerides also play a causal role in heart disease.[ref]
People are starting to take note of triglyceride levels as a marker of metabolic syndrome. The defining factors for metabolic syndrome include abdominal obesity, high blood pressure, high blood sugar, low HDL, and high triglycerides.
The immediate response to ‘why do I have high triglycerides’ is to blame the diet and assume you are eating donuts and drinking lots of soda. While diet does play a role (of course), your genetic variants are also very important in basal triglyceride levels.
Triglycerides – three fatty acids and glycerol – can contain either saturated or unsaturated fatty acids. Most triglycerides contain different types of fatty acids in them.
Saturated fats are carbon-hydrogen chains that have single bonds between all the carbons. Unsaturated fats have either one double bond (monounsaturated) or multiple double bonds (polyunsaturated). The double bonds cause a bend in the molecule, keeping it from packing together as tightly. Thus polyunsaturated fats are usually liquids and saturated fats can be solids at room temperature.
Triglycerides from food cannot be directly absorbed. They are emulsified by lipase, an enzyme secreted by the pancreas to break down fats. In the enterocytes of the small intestines, the fatty acids from triglycerides are packaged into chylomicrons (like a glob of fat). Picture how oil clumps together into droplets when you try to stir it into water.
Chylomicrons contain mostly triglycerides along with a smaller percentage of cholesterol, phospholipids, and proteins. They are secreted into the lymphatic system first, so they don’t go through the liver first like amino acids and sugars.
Testing of triglyceride levels is usually done in a fasted state because the blood levels of triglycerides can rise quite a bit after eating.
Plasma triglyceride tests measure the VLDL and chylomicrons.
Triglyceride level ranges [ref]:
To convert mg/dl triglyceride levels into mmol/L, multiply by .01129.
In studies, hypertriglyceridemia is usually defined as being higher than 150 mg/dl or higher than 2 mmol/L (175mg/dl). About 25% of adults in the US meet this criterion.[ref][ref] Other studies call levels from 150-999 mg/dl mild to moderate hypertriglyceridemia. Levels over 1,000 mg/dl are severe and can cause pancreatitis.[ref]
High triglycerides are linked to atherosclerosis and stroke. Is this a big increase in risk? That is a hard question to quantify since every study seems to have different endpoints and biases.
Here are some study results:
There have been several studies showing that high fructose intake increases triglycerides. This may lead you to assume that drinking the periodic soda is causing your high triglycerides…
The animal studies pretty clearly show that fructose increases triglyceride levels. In rats, replacing water with fructose water increases blood pressure, liver fat, and triglycerides pretty significantly. [ref] [ref]
Human studies on fructose and triglycerides show similar trends, but much less dramatic results.
A study using normal weight adults looked at the difference between consuming 150g/d of fructose or 150 g/day of glucose for 4 weeks. They did this by substituting the fructose or glucose for other calories in the diet, so overall calories weren’t affected. After 4 weeks, there was no increase in visceral fat, muscle fat, or liver fat and no changes to blood pressure. In fact, the only change after 4 weeks was that triglycerides in the fructose group went up by 35 mg/dl (still in the normal range, though). There was no change in triglycerides in the glucose group.[ref]
Studies in humans where fructose is added on top of their normal caloric intake do show a larger increase in triglyceride. One study that added fructose for a 35% increase in calories showed triglyceride levels rising 75%.[ref] But it is hard to differentiate between suddenly adding that many calories vs. those calories being from fructose. [ref]
A meta-analysis of a bunch of studies concluded there is no difference on triglyceride levels from fructose vs sucrose vs glucose.[ref]
Leptin is the hormone that signals to the brain that you are full and don’t need to eat. In people who are overweight or obese, there is usually a high level of leptin, but that signal isn’t being received in the brain (leptin resistance). The question is ‘why’… One theory is that elevated triglyceride levels interact with leptin in the brain, causing the leptin resistance.
Triglyceride levels rise when you are in a state of starvation as your body activates fat from adipose tissue. A recent study recently looked at the connection between triglyceride levels and leptin resistance. The study found that triglycerides do cross the blood-brain barrier and can induce leptin resistance. [ref – open access]
Theoretically, it makes sense that in times of starvation, high triglycerides would block the leptin signal, driving people to need more food. But in our modern epidemic of metabolic syndrome and high triglyceride levels, this is causing leptin resistance and increasing the desire to eat even when overweight.
High triglyceride levels usually correspond to lower HDL levels. This is part of what makes research on cardiovascular disease risk and triglycerides difficult — is it the low HDL or high triglycerides that cause the increase in risk? [ref – open access]
Below are some of the more common (found in >1% of the population) genetic variants that affect triglyceride levels. Most studies now point to the interaction between these variants. For example, if you carry a couple of the variants that raise your triglyceride levels, it may be causing your high triglycerides. But carrying a couple of the variants that lower your triglycerides along with one that raises it could give you a normal triglyceride level (depending on diet).
What is missing from this list is the rare mutations that cause hypertriglyceridemia.
The APOA5 gene codes for apolipoprotein A5, which is a lipoprotein that is involved in triglyceride levels, possibly through activating lipoprotein lipase (LPL).
The lipoprotein lipase (LPL) enzyme releases fatty acids to be used as fuel. It does this by hydrolyzing the triglycerides in plasma lipoproteins. Genetic variants that decrease this enzyme can raise triglyceride levels.
Glucokinase regulatory protein regulates glucose kinase, a sensor that regulates glucose from glycolysis.
The APOE E4 variant is also tied to a risk of increased triglyceride levels. If you want to know your APOE status, read through the article on Alzheimer’s disease and APOE.
What are we missing here? Rare mutations…
Here are a few that are covered in 23andMe or AncestryDNA. But this is just the tip of the iceberg for rare variants that could have a large impact on high triglycerides. What does ‘rare’ mean — usually that the mutation is found in less than 1 in 1000 people.
If you have high triglycerides, carrying some of the variants (above) that raise your triglyceride levels is part of the problem. The other half of the equation is diet and lifestyle.
It is pretty clear that high fructose corn syrup increases triglyceride levels. So cut out the soda or switch to drinks without high fructose corn syrup.
Even more noteworthy, a ketogenic diet was shown in a (small) study to reduce triglyceride levels fairly significantly. [ref]
The Mediterranean diet was shown in a trial to reduce triglycerides (a little). [ref]
There are prescription formulations of omega-3 fatty acids that are prescribed for high triglycerides. They have been shown in several trials to reduce triglyceride levels and VLDL levels.[ref]
An obvious alternative to prescription omega-3s is to take fish oil supplements or eat more fish. This has been shown in studies to reduce high triglycerides in people with non-alcoholic fatty liver disease.[ref] [ref]
In rat studies, resveratrol prevents the rise in triglycerides due to fructose supplementation. [ref] Human studies on non-alcoholic fatty liver disease show mixed (or little) benefit from resveratrol on triglycerides.[ref]
Betaine (TMG) and choline:
Betaine and/or choline may influence triglyceride levels. Adding in more choline, either as betaine (TMG) or in another form may help to lower triglycerides. Betaine is shown to be higher in people with lower triglyceride levels.[ref][ref]
A mouse study showed that adding betaine to the diet of APOE deficient mice caused triglycerides to go down.[ref]
Niacin has long been recommended as a way to decrease cardiovascular disease risk. Study results, though, are kind of all over the place as far as how much niacin really helps when looking at mortality rates from heart attacks.[ref] Studies do show that niacin supplementation reduces triglyceride levels for most, but the long term effects on liver function warrants caution.[ref][ref]
l-carnitine supplements have been shown in animal studies to reduce triglyceride levels.[ref]