Magazine article Nutrition Health Review

An Overlooked Risk Factor in Heart Disease: An Interview with Sarah Berry, M.D

Magazine article Nutrition Health Review

An Overlooked Risk Factor in Heart Disease: An Interview with Sarah Berry, M.D

Article excerpt


Q: What are triglycerides?

A: Dietary fat consists predominantly of triglycerides (TGs). Also called triacylglycerols (TAGs), triglycerides consist of a glycerol backbone to which three fatty acids are linked. Fatty acids differ in their chain length, number, position, and geometry (c/'s or trans) of their double bonds. These differences determine the properties of the fatty acids, such as their melting characteristics, solubility in water, and health properties. Fatty acids that have all the carbon atoms in the chain linked by single bonds are called saturated fatty acids (SFAs).

Unlike SFAs, unsaturated fatty acids contain one double bond (monounsaturated fatty acid [MUFAs]) or more double bonds (polyunsaturated fatty acid [PUFAs]) at specific positions in the carbon chain. The nature of TGs, and dietary fat therefore, is determined by their fatty acid constituents. Most dietary fats consist of a mixture of SFAs, MUFAs, and PUFAs. Fats that are rich in SFAs tend to be solid at room temperature; fats rich in MUFAs and PUFAs tend to be liquid at room temperature.

Q: What is the purpose of triglycerides?

A: TGs are an important energy source at 9 kilocalories per gram, (kcal./g.), compared with 4 kcal./g, for carbohydrate and protein. This is particularly important for newborns and young children, who have high energy demands.

As TGs deliver the fatty acids in dietary fat, they are also important for the absorption of fat soluble vitamins (A, D, E, and K) and for providing essential fatty acids (omega-3 and omega-6). These fatty acids have a whole host of functions of their own, such as cell structure and signaling, growth, gene expression and production of eicosonoids. They make food more palatable by giving a creamy mouth-feel to food. They also act as a solvent to flavors.

Q: Does the body manufacture tyiglycerides, or are they found in foods?

A: The body is able to make fatty acids and TGs from excess dietary carbohydrate; however, it is not able to make the essential fatty acids (omega-3 and omega-6). That is why they are called essential. Different kinds of fatty acids and therefore TGs can be found in various foods; this is why, as with all nutrients, it is important to get a healthy balance of different foods.

Q: What is a normal blood triglyceride level?

A: Normal TG levels range between 0.5 and 2.0 millimoles per liter (mmol./L.), but they increase following a meal containing fat; thus, it is important to measure levels in the fasting state. Fasting guidelines are below 1.7 mmol./L.

Q: What role do triglycerides play in heart disease?

A: Plasma TGs are an independent risk factor for cardiovascular disease (CVD). A recent meta-analysis reported that each 1 mmol./L. increase in TGs increased the relative risk of CVD by 14 percent in men and 37 percent in women after adjustment for high-density lipoprotein-cholestrol (HDL-C) levels. However, it is argued that they should be considered more as a marker for risk rather than as an independent factor, thus keeping the focus on cholesterol.

Fasting values and postprandial (after-meal) values influence a number of mechanisms involved in the atherosclerotic processes. TGs circulate in the blood in specialized lipoproteins, collectively called TG-rich lipoproteins, particularly very-low-density lipoproteins (VLDLs) and chylomicrons). These TG-rich lipoproteins have a direct atherogenic effect. Furthermore, elevated TG levels may influence mechanisms associated with the development of CVD, including thrombogenesis (blood clotting), endothelial dysfunction (impairment of the vascular wall), and oxidative stress.

Q: How do triglycerides differ from cholesterol?

A: Both TGs and cholesterol circulate in the blood and originate in part from the diet (an exogenous source); they are also produced by the body (an endogenous source). …

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