Dietary fats, from olive oil to cocoa butter to beef tallow, are made of triglycerides.
Triglycerides are simply three (“tri-”) fatty acids attached to a glycerol backbone. Glycerol is a simple 3-carbon molecule that readily binds fatty acids. Fatty acids, of course, can be saturated, polyunsaturated, and monounsaturated.
Once ingested, the action of the pancreatic enzyme, pancreatic lipase, along with bile acids secreted by the gallbladder, remove triglycerides from glycerol. Triglycerides pass through the intestinal wall and are “repackaged” into large complex triglyceride-rich (about 90% triglycerides) molecules called chylomicrons, which then pass into the lymphatic system, then to the bloodstream. The liver takes up chylomicrons, removes triglycerides which are then repackaged into triglyceride-rich very low-density lipoproteins (VLDL).
So eating triglycerides increases blood levels of triglycerides, repackaged as chylomicrons and VLDL.
Many physicians are frightened of dietary triglycerides, i.e, fats, for fear it will increase blood levels of triglycerides. It’s true: Consuming triglycerides does indeed increase blood levels of triglycerides–but only a little bit. Following a fat-rich meal of, say, a 3-egg omelet with 2 tablespoons of olive oil and 2 oz whole milk mozzarella cheese (total 55 grams triglycerides), blood triglycerides will increase modestly. A typical response would be an increase from 60 mg/dl to 80 mg/dl–an increase, but quite small.
Counterintuitively, it’s the foods that convert to triglycerides in the liver that send triglycerides up, not 20 mg/dl, but 200, 400, or 1000 mg/dl or more. What foods convert to triglycerides in the liver? Carbohydrates.
After swallowing a piece of multigrain bread, for instance, carbohydrates are released by salivary and gastric amylase, yielding glucose molecules. Glucose is rapidly absorbed through the intestinal tract and into the liver. The liver is magnificently efficient at storing carbohydrate calories by converting them to the body’s principal currency of energy, triglycerides, via the process of de novo lipogenesis, the alchemy of converting glucose into triglycerides for storage. The effect is not immediate; it may require many hours for the liver to do its thing, increasing blood triglycerides many hours after the carbohydrate meal.
This explains why people who follow low-fat diets typically have high triglyceride levels–despite limited ingestion of triglycerides. When I cut my calories from fat to 10% or less–a very strict low-fat diet–my triglycerides are 350 mg/dl. When I slash my carbohydrates to 40-50 grams per day but ingest unlimited triglycerides like olive oil, raw nuts, whole milk cheese, fish oil and fish, etc., my triglycerides are 50 mg/dl.
Don’t be afraid of triglycerides. But be very careful with the foods that convert to triglycerides: carbohydrates.