Triglycerides: the neglected but important cholesterol
Triglycerides is a term that most of us recognize. This substance is part of the lipid (cholesterol) profile. However, this may be the extent of our understanding. Compared to the other substances, HDL (“good” cholesterol) and LDL (“bad” cholesterol), triglycerides are not covered much in the lay press, and medical research tends to be less robust than for the other components. If I were to use a baseball analogy, triglycerides are the Mets, who get far less attention than their crosstown rivals, the Yankees. Although last year, the Mets received the attention they deserved, so let’s see if this year we can get triglycerides the attention they deserve.
But are triglycerides any less important than other parts of the cholesterol profile? It is unclear whether a high triglyceride level is a biomarker for cardiovascular disease — heart disease and stroke — or an independent risk in its own right (1, 2). This debate has been going on for over 30 years. Either way, it still means triglycerides are important.
What are triglycerides? The most rudimentary explanation is that they are a kind of fat in the blood. Triglycerides are composed of sugar alcohol and three fatty acids. Thus, it is no surprise that alcohol, sugars and excess calorie consumption may be converted into triglycerides.
Risk factors for high triglycerides include obesity, smoking, a high carbohydrate diet, uncontrolled diabetes, hypothyroidism (underactive thyroid), cirrhosis (liver disease), excessive alcohol consumption and some medications (3).
What levels are normal and what are considered elevated? According to the American Heart Association, optimal levels are <100 mg/dL; however, less than 150 mg/dL is considered within normal range. Borderline triglycerides are 150-199 mg/dL, high levels are 200-499 mg/dL and very high are >500 mg/dL (3).
While medicines that focus on triglycerides, fibrates and niacin, have the ability to lower them significantly, it is questionable whether this reduction results in clinical benefits, such as reducing the risk of cardiovascular events. The ACCORD Study, a randomized controlled trial, questioned the effectiveness of medication; when these therapies were added to statins in type 2 diabetes patients, they did not further reduce the risk of cardiovascular disease and events (4). Instead, it seems that lifestyle modifications may be the best way to control triglyceride levels. Let’s look at the evidence.
Exercise — timing and intensity
If you need a reason to exercise, here is really good one. I frequently see questions pertaining to optimal exercise timing and intensity. Most of the answers are vague, and the research is not specific. However, hold on to your hats because a recent study may give the timing and intensity answer, at least in terms of triglycerides.
Study results showed that walking a modest distance with alacrity and light weight training approximately an hour after eating (postprandial) reduced triglyceride levels by 72 percent (5). However, if patients did the same workout prior to eating, postprandial triglycerides were reduced by 25 percent. This is still good, but not as impressive. Participants walked a modest distance of just over one mile (2 kilometers). This was a small pilot study of 10 young healthy adults for a very short duration. The results are intriguing nonetheless, since there are few data that give specifics on the optimal amount and timing of exercise.
Exercise trumps calorie restriction
There is good news for those who want to lower their triglycerides: calorie restriction may not be the best answer. In other words, you don’t have to torture yourself by cutting calories down to some ridiculously low level to get an effect. We probably should be looking at exercise and carbohydrate intake instead.
In a well-controlled trial, results showed that those who walked and maintained 60 percent of their maximum heart rate, which is a modest level, showed an almost one-third reduction in triglycerides compared to the control group (maintain caloric intake and no exercise expenditure) (6). Those who restricted their calorie intake saw no difference compared to the control. This was a small study of 11 young adult women. Thus, calorie restriction was trumped by exercise as a way to potentially reduce triglyceride levels.
Carbohydrate reduction not calorie restriction
In addition, when calorie restriction was compared to carbohydrate reduction, results showed that carbohydrate reduction was more effective at lowering triglycerides (7). In this small but well-designed study, patients with nonalcoholic fatty liver disease were randomized to one of two diets, lower calorie (1200-1500 kcal/day) or lower carbohydrate (20 g/day). Both groups significantly reduced triglycerides, but the lower carbohydrate group reduced triglycerides by 55 percent versus 28 percent for the lower calorie group. The reason for this difference may have to do with oxidation in the liver and the body as a whole. Both groups lost similar amounts of weight, so weight could not be considered a confounding or complicating factor. However, the weakness of this study was its duration of only two weeks.
Fasting versus nonfasting blood tests
The paradigm has been that, when cholesterol levels are drawn, fasting levels provide a more accurate reading. Except this may not be true.
In a new analysis, fasting may not be necessary when it comes to cholesterol levels. NHANES III data suggest that nonfasting and fasting levels yield similar results related to all-cause mortality and cardiovascular mortality risk. The LDL levels were similarly predictive regardless of whether a patient had fasted or not. The researchers used 4,299 pairs of fasting and nonfasting cholesterol levels. The duration of follow-up was strong, with a mean of 14 years (8).
Why is this relevant? Triglycerides are an intricate part of a cholesterol profile. With regards to stroke risk assessment, nonfasting triglycerides possibly may be more valuable than fasting. In a study involving 13,596 participants, results showed that as nonfasting triglycerides rose, the risk of stroke also rose significantly (9). Compared to those who had levels below 89 mg/dL (the control), those with 89-176 mg/dL had a 1.3-fold increased risk of cardiovascular events, whereas those within the range of 177-265 mg/dL had a twofold increase, and women in the highest group (>443 mg/dL) had an almost fourfold increase. The results were similar for men, but not quite as robust at the higher end, with a threefold increase.
The benefit of nonfasting is that it is more realistic and, according to the authors, also involves remnants of VLDL and chylomicrons, other components of the cholesterol profile that interact with triglycerides and may affect the inner part (endothelium) of the arteries.
What have we learned? Triglycerides need to be discussed, just as we review HDL and LDL levels regularly. Elevated triglycerides may result in heart disease or stroke. The higher the levels, the more likely there will be increased risk of mortality — both all-cause and cardiovascular. Therefore, we ideally should reduce levels to less than 100 mg/dL.
Lifestyle modifications using carbohydrate restriction and modest levels of exercise after a meal may be the way to go to achieve the best results, though the studies are small and need more research. Nonfasting levels may be as important as fasting levels when it comes to triglycerides and the cholesterol profile as a whole; they potentially give a more realistic view of cardiovascular risk, since we don’t live in a vacuum and fast all day.
(1) Circulation. 2011;123:2292-2333. (2) N Engl J Med. 1980;302:1383–1389. (3) nlm.nih.gov. (4) N Engl J Med. 2010;362:1563-1574. (5) Med Sci Sports Exerc. 2013;45(2):245-252. (6) Med Sci Sports Exerc. 2013;45(3):455-461. (7) Am J Clin Nutr. 2011;93(5):1048-1052. (8) Circulation Online. 2014 July 11. (9) JAMA 2008;300:2142-2152.
Dr. Dunaief is a speaker, author and local lifestyle medicine physician focusing on the integration of medicine, nutrition, fitness and stress management. For further information, go to the website www.medicalcompassmd.com or consult your personal physician.