In recent years, obesity has become increasingly severe. Research has revealed that the combination of high-fat, high-calorie diets and moderate-intensity exercise may pose unexpected health risks. Experiments show that while moderate exercise can improve metabolic indicators and reduce fat accumulation, it may exacerbate heart damage caused by high-fat diets.
In recent years, obesity has become a major global public health challenge, with its impact spreading from developed countries to developing nations. According to a 2024 study published in The Lancet, the global obese population has surpassed 1 billion.
When delving into the root causes of obesity, two key factors emerge: high-calorie diets and a lack of physical activity. After indulging in high-calorie meals, do you find yourself rushing to the gym or the sports field to burn off the extra calories? Surprisingly, this habit might not be as healthy as it seems!
Recently, researchers from China conducted a study that revealed a startling fact: while moderate-intensity intermittent exercise can reduce overall fat accumulation, it may also exacerbate heart damage, particularly in the context of high-fat, high-calorie diets.
Study Design and Methods
This study utilized C57BL/6J mice as experimental subjects. Over eight weeks, the mice were subjected to different dietary treatments: one group received a standard diet (10% of calories from fat), while the other group was fed a high-fat, high-calorie diet (HFCD, 60% of calories from fat) to simulate unhealthy human dietary habits.
After the dietary intervention, mice from both the standard diet and HFCD groups were randomly assigned to one of three exercise intensity groups: low-intensity exercise (LIE), moderate-intensity exercise (MIE), or high-intensity exercise (HIE). Each group followed a specific training regimen.
To assess the effects of exercise intensity on heart health, researchers monitored various physiological parameters, including weight changes, blood glucose levels and trends over time, serum triglycerides, total cholesterol, HDL, LDL levels, white adipose tissue (WAT) weight, and serum insulin levels. Additionally, the researchers traced lipid distribution using ^13C-labeled palmitic acid and fluorescent dyes, and employed tissue staining to visually observe lipid deposition in the liver, skeletal muscle, and WAT.
Effects of Moderate-Intensity Exercise on Whole-Body Metabolism and Heart Function
The obesity model was successfully established, with HFCD-fed mice exhibiting significant weight gain, elevated blood glucose, triglycerides (TAG), total cholesterol (Chol), HDL, LDL levels, and increased WAT weight compared to the standard diet (CD) group.
Moderate-intensity exercise (MIE) was selected for focused study due to its reported benefits for weight loss and heart health. Interestingly, although MIE increased food intake and caloric consumption in both CD- and HFCD-fed mice, it significantly reduced body weight, blood glucose, TAG, and Chol levels. This indicates that MIE can prevent obesity, hyperglycemia, and hyperlipidemia in HFCD-fed mice. MIE also reduced WAT weight in HFCD-fed mice, although it did not improve insulin sensitivity.
Figure: Moderate-intensity exercise prevents obesity and metabolic syndrome in HFCD-fed mice
However, the study presented an unexpected twist: while MIE improved certain metabolic parameters, it failed to protect against HFCD-induced cardiac dysfunction. Alarmingly, MIE actually exacerbated cardiac damage in HFCD-fed mice. Specifically, MIE increased cardiac hypertrophy, elevated markers of cardiac fibrosis, and raised levels of biomarkers associated with pathological hypertrophy.
Impact of Exercise Intensity on Cardiac Health in HFCD-Fed Mice
The results showed that all three exercise intensities prevented the progression of obesity and metabolic syndrome in HFCD-fed mice, with high-intensity exercise being the most effective. However, echocardiographic results revealed a concerning trend: while low-intensity exercise improved cardiac health, both moderate- and high-intensity exercise exacerbated cardiac dysfunction in HFCD-fed mice, increasing cardiac damage and pathological changes.
Figure: High-intensity and moderate-intensity exercise exacerbate HFCD-induced cardiac dysfunction, while low-intensity exercise improves cardiac health
Mechanisms Behind MIE-Induced Cardiac Damage in HFCD-Fed Mice
Further analysis uncovered complex mechanisms by which MIE affects cardiac health. In HFCD-fed mice, MIE redistributed lipids from the liver and WAT to the heart, significantly increasing cardiac lipid uptake. Simultaneously, it impaired cardiac fatty acid oxidation (FAO), leaving cardiomyocytes unable to process the excess lipids effectively, leading to increased lipid accumulation in the myocardium.
Moreover, MIE inflicted a "double hit" on cardiac function in HFCD-fed mice: it further disrupted FAO and mitochondrial function. Experimental data showed reduced activity in mitochondrial respiratory chain complexes, impairing energy production efficiency. Additionally, mitochondrial morphology and structure were altered, indicating severe health deterioration. These changes collectively contributed to disrupted cardiac energy metabolism, heightening the risk of heart damage.
Figure: Moderate-intensity exercise (MIE) exacerbates HFCD-induced cardiac lipid accumulation
Conclusion
This study highlights an important finding: under certain circumstances, exercise can have adverse effects, especially for individuals consuming high-calorie diets. Increasing exercise alone may not be the best solution for addressing such challenges. The study also underscores the importance of personalized health management, as each individual's condition is unique, requiring tailored exercise approaches.
Lastly, the research serves as a cautionary reminder: when pursuing weight loss or body shaping, it is crucial to avoid the pitfalls of combining overeating with excessive exercise. Only by adopting a balanced, sustainable approach can we achieve true health and well-being!