Weight Training, Aerobic Exercise Affect Cardiac Fat Mass in Different Ways

Aerobic exercise and resistance training with weights are both effective in reducing epicardial fat mass in individuals with abdominal obesity, but resistance training appears to be a better exercise for reducing pericardial adipose tissue mass, according to the results of a new study. 

When compared with individuals who did no exercise at all, those who engaged in aerobic and resistance training had a significant 32% and 24% reduction in epicardial adipose tissue mass, respectively. On the other hand, compared with the control group, endurance exercise had no significant effect on pericardial adipose tissue mass after 12 weeks, but there was a 31% reduction in pericardial fat mass in those who engaged in strength training (P < 0.001).

Having a better understanding of these two types of cardiac fat—and how to target them—may be important for risk management, the authors say. Epicardial adipose tissue is metabolically active and is believed to directly impact coronary and cardiac function given its intimate relationship to the heart muscle, while less is known about the effect of pericardial fat mass on heart function. 

“It is possible that the small study was the reason for the lack of effect of endurance training on pericardial adipose tissue mass,” Regitse Højgaard Christensen, MD (University of Copenhagen, Denmark), told TCTMD. Nonetheless, “we know from other studies that resistance training is a stronger stimulus for increased muscle mass and increased basal metabolism compared to endurance training and we speculate that participants doing resistance training burn more calories during the day—also in inactive periods—compared to those engaging in endurance training.”

That theory explaining the differential effects on pericardial fat mass needs to be tested in a future study, however, said Christensen.

On the whole, the study provides exploratory evidence that different exercise modalities performed according to current exercise guidelines target cardiac adipose tissue in addition to the other health benefits of exercise. “This was even without a concomitant diet restriction,” said Christensen. “Therefore, the study emphasizes that practicing physicians motivate patients at risk of cardiovascular disease to engage in any type of exercise as a preventative measure.”

Metabolically Active Epicardial Adipose Tissue

The study, which was published online July 3, 2019, ahead of print in JAMA Cardiology, is a secondary analysis from a larger randomized exercise intervention study of inactive subjects with abdominal obesity. In this substudy, 50 individuals were randomized to endurance training, resistance training, or to the control arm, which involved no exercise. Endurance training included three weekly training sessions of high-intensity interval exercise on an ergometer bicycle for 45 minutes over a 12-week period. Resistance training was designed to include medium loads and high repetitions performed in three to five sets of 10 exercises. Cardiac adipose tissue mass was measured using MRI. Overall, 39 participants completed the study.

Epicardial adipose mass—the layer of fat that surrounds the heart muscle and embeds the coronary arteries—was unchanged in those who did no exercise, but was reduced by 8 and 6 g from baseline in the endurance and resistance training arms, respectively. Compared with the control group, the reduction with both training programs was statistically significant, but the effect of resistance versus endurance training on epicardial adipose mass was not different (P = 0.58).

Pericardial adipose mass was reduced 10, 15, and 43 g from baseline in the control, endurance, and resistance training arms, respectively. The reduction in pericardial fat mass with endurance training did not differ compared with the no-exercise group, whereas the reduction with resistance training was statistically significant compared with the control arm. Compared with endurance training, the pronounced reduction in pericardial adipose mass with resistance exercise was statistically significant (P = 0.003).

To TCTMD, Christensen said that epicardial adipose tissue, the inner layer of the two fat depots, is believed to secrete inflammatory adipokines that provoke atherosclerosis as the adipose tissue accumulates and expands. Recent studies, said Christensen, suggest that epicardial adipose tissue may be a new risk factor for cardiovascular disease and may add incremental value when added to current risk prediction algorithms.

“The pericardial adipose tissue is located outside of the epicardial [tissue],” she said. “Even though the two adipose tissue depots are close, they are different. They are of a different origin. Epicardial adipose tissue is highly metabolically active, and while the epicardial tissue shares blood supply with the heart muscle, the pericardial adipose tissue is supplied by other blood vessels in the thoracic cage.”

Given its lack of direct contact with the heart, pericardial adipose tissue may impact heart function in a more indirect way, although less is known about pericardial adipose tissue as a cardiovascular risk factor, said Christensen.

Another Mechanism for Exercise’s Benefits

Commenting on the paper for TCTMD, Aaron Baggish, MD (Massachusetts General Hospital, Boston), said the study adds to list of mechanisms in which exercise confers health benefits. “Exercise is good for you, which we all know,” he said. “We know it moves traditional cardiovascular disease risk factors in the right direction—blood pressure, cholesterol—but none of that really explains the whole story. So to add the epicardial and pericardial fat part of the story, as well as the [reduction in] epigastric fat, to this is a really interesting finding.” 

Satyam Sarma, MD (UT Southwestern Medical Center, Dallas, TX), who was also not involved in the research, stated that the study helps build on current knowledge about the beneficial effects of exercise on ectopic fat depots, and shows that “engaging in a structured exercise program improves metabolic health.” Like Baggish, he noted that resistance training reduced abdominal fat mass and waist circumference, but how these reductions translate into improvements in fat distribution around the heart is not well understood.

“It may be that any form of exercise, whether it be strength or endurance training, reduces fat indiscriminately across different depots,” Sarma told TCTMD in an email. “Alternatively, it may be that increasing lean muscle through endurance training helps promote specific endocrine pathways that preferentially reduce pericardial adipose tissue.”

Baggish suggested that the lack of meaningful reduction in pericardial fat with endurance training is likely a type 2 error because the study was underpowered. “They have such small numbers, that when you apply any sort of statistical test to it, if one or two people move in the wrong direction, it’s going to cause the P value to fall on the wrong side of 0.05,” he said. “Honestly, having done a lot of repeated measures’ studies, if I had a dime for every time the P value was 0.06, I’d be a rich man. If you look at the primary data, the results are pretty clear—any sort of exercise, whether it’s resistance or endurance training, does good things with respect to fat deposition and that’s a solid addition to the literature.”

For Baggish, the study should not discourage individuals from endurance activity, or to prioritize resistance training. “The bulk of the literature would suggest endurance activity is really the key,” he said. “Resistance activity is important but not to the level that you should ever choose it as opposed to aerobic-based work.”