Burn Belly Fat, Boost Health: HIIT & SIT vs. Traditional Exercise

Battling obesity and its health risks? This review, published in Frontiers in Physiology, highlights the power of exercise, especially high-intensity interval training (HIIT) and sprint interval training (SIT), in tackling belly fat and boosting metabolic health. While traditional low-intensity workouts burn fat slowly, HIIT/SIT primarily use carbs during exercise. However, they still effectively reduce overall fat, especially the harmful visceral fat in the abdomen. The exact mechanisms are unclear, but exercise might improve fat storage and reduce inflammation, leading to less belly fat even with carb-burning workouts. More research is needed to fully understand these mechanisms, but the bottom line is clear: exercise, especially HIIT and SIT, is a powerful tool to combat obesity and improve your health, even if the science behind it isn't fully there yet.

Key Points:

• Obesity, especially abdominal fat, increases the risk of various diseases. This highlights the need for effective methods to achieve a negative energy balance for weight management.

• Lifestyle changes, including exercise, are crucial for managing obesity. While weight loss can involve reducing calorie intake or increasing energy expenditure, the latter proves challenging for obese individuals.

• Exercise intensity influences energy source and duration. Low-intensity exercise utilizes fat as the primary fuel for prolonged periods. Conversely, carbohydrates become the main source during high-intensity workouts, which are typically shorter in duration.

• High-intensity interval training (HIIT) and sprint interval training (SIT) offer time-efficient alternatives. Despite using carbohydrates predominantly during exercise, HIIT and SIT effectively reduce total fat mass, suggesting alternative mechanisms at play.

• Fat localization plays a significant role in metabolic health. Visceral adipose tissue (VAT) in the abdomen is particularly detrimental. Reducing VAT is crucial for improving metabolic outcomes.

• Obesity-related insulin resistance disrupts fat storage and contributes to ectopic lipid deposition. This further worsens metabolic health.

• Exercise training may improve adipose tissue function, even without significant fat oxidation during exercise. This could involve increased fat storage capacity, reduced overflow, and decreased inflammation, ultimately leading to reduced abdominal fat and ectopic lipid deposition.

Energy Expenditure in the Human Body

Humans today expend significantly less energy due to our sedentary lifestyles compared to our hunter-gatherer ancestors. This mismatch between energy intake and expenditure contributes to the rising prevalence of obesity.

To understand energy expenditure, we need to define key terms:

• Total daily energy expenditure (TDEE): total energy used in a day, measured using the doubly labelled water (DLW) method.

• Resting energy expenditure (REE): energy used during complete rest.

• Activity-related energy expenditure (AEE): energy used during daily activity and exercise.

• Thermic effect of food (TEF): energy used to digest and process food (not included in calculations here).

The REE, which depends on body size and composition, makes up about 60% of TDEE. Physical activity typically contributes less than 40% of TDEE for most people. This highlights the challenge of exceeding REE through activity alone for weight management.

Energy Expenditure During Exercise

This article explores the effects of exercise on energy expenditure and fat loss, focusing on the differences between high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT). Key points include:

• Energy expenditure: Both HIIT and MICT increase energy expenditure, but HIIT requires less time commitment for similar levels of energy use.

• Fat loss: While both methods can lead to fat loss, the mechanisms differ. HIIT may result in greater fat loss despite lower total energy expenditure due to potential improvements in metabolic flexibility and EPOC (excess post-exercise oxygen consumption).

• Metabolic adaptations: Both methods improve VO2 max (maximal oxygen uptake) and reduce abdominal fat, fasting glucose, and HbA1c. HIIT may activate AMPK and PGC-1α signaling to a greater extent, potentially further influencing metabolic health.

• Body composition: Exercise training can shift body composition by reducing fat mass and increasing muscle mass, even without overall weight loss.

• Limitations: Studies on the exact mechanisms of fat loss and the role of increased mitochondrial oxidative capacity are still ongoing.

Energy Expenditure after Exercise

High-intensity interval training (HIIT) and sprint interval training (SIT) burn the same amount of fat as moderate-intensity continuous training (MICT) but require less time, suggesting improved fat loss efficiency. This could be due to an increase in resting energy expenditure (REE) after HIIT, but no direct evidence supports this. Alternatively, participants might not compensate for HIIT's energy expenditure by adjusting their food intake. The most likely explanation is the elevated post-exercise oxygen consumption (EPOC) caused by HIIT, which burns additional calories even after exercise ends. The exact biological mechanisms of EPOC are still debated, but they likely involve muscle repair and replenishing energy stores, which in turn require the body to tap into fat stores. Additionally, HIIT might improve metabolic flexibility, allowing the body to burn more fat at rest. While brown adipose tissue plays a role in thermogenesis in infants, its function in adults is unclear. White adipose tissue (WAT) stores energy but also secretes hormones that affect metabolism. Excessive body fat, measured by methods like MRI or DXA scans, is linked to health problems and hinders exercise performance. While BMI has limitations, both BMI and total fat mass are associated with an increased risk of obesity-related diseases. Overall, HIIT and SIT offer time-efficient fat loss benefits, potentially due to EPOC and improved metabolic flexibility, but further research is needed to fully understand the mechanisms at play.░

Metabolic Differences in Fat Depots

Not all fat is created equal! Different fat depots in the body show distinct metabolic behaviors and health implications. The two main players are visceral adipose tissue (VAT), - fat surrounding internal organs, and subcutaneous white adipose tissue (SAT), found under the skin. Men tend to accumulate more abdominal fat (abdominal VAT), while women store more gynoid fat (hips and legs). Interestingly, research suggests gynoid fat might even be protective against heart disease, while excess abdominal fat significantly increases the risk of type 2 diabetes, fatty liver disease, and cardiovascular issues. This risk persists even in individuals with normal weight if their fat distribution leans heavily towards VAT.

The reasons behind VAT's harmful nature are still being investigated, but potential culprits include:

• Direct access to the liver: The portal vein drains blood from VAT directly to the liver, potentially flooding it with harmful factors.

• Different signaling: VAT adipocytes have varying adrenergic receptors compared to SAT, potentially impacting metabolic responses.

• Overflow storage: When SAT storage capacity is maxed out, excess fat might spill over into harmful VAT deposits.

Adipose Tissue Dysfunction and its Impact on Metabolic Health:

Fat distribution matters! Beyond just total body fat, where fat is stored significantly impacts health. In individuals with obesity or type 2 diabetes, adipose tissue (AT) becomes dysfunctional, marked by:

• Hypertrophic adipocytes: large, dysfunctional fat cells linked to insulin resistance and heart disease risk.

• Macrophage infiltration: Increased inflammatory immune cells worsen low-grade inflammation.

• Apoptosis and impaired angiogenesis: Dying fat cells and disrupted blood vessel formation create a vicious cycle.

These features contribute to:

• Low-grade inflammation: constant immune activation throughout the body.

• Fat overflow: Excess fat spills over to organs like the liver and muscles, harming their function.

• Ectopic lipid deposition: Fat accumulation in harmful places like the pancreas disrupts insulin production.

The consequences are widespread:

• Insulin resistance: cells become less responsive to insulin, leading to type 2 diabetes risk.

• Non-alcoholic fatty liver disease (NAFLD): Liver function is compromised by fat buildup.

• Cardiovascular disease (CVD): Increased inflammation and altered fat metabolism contribute to heart problems.

Exercise and Metabolic Health: Key Takeaways

• Regular physical activity is crucial for managing weight and metabolic diseases like type 2 diabetes, cardiovascular disease, and non-alcoholic fatty liver disease (NAFLD).

• While medication exists for diabetes and cardiovascular disease, NAFLD treatment options are limited. Exercise effectively combats NAFLD, but the underlying mechanisms are still being explored.

• Exercise improves insulin sensitivity and glucose tolerance, primarily by influencing proteins involved in glucose metabolism and the insulin signaling pathway within muscles. Similar changes are likely to occur in adipose tissue.

• Despite increased energy expenditure during exercise, weight loss might not always occur due to the body's complex energy balance.

• Exercise can improve body composition by reducing fat mass and increasing muscle mass, even without overall weight loss.

• High-intensity interval training (HIIT) and sprint interval training (SIT) offer similar metabolic benefits as moderate-intensity continuous training (MICT) in terms of improving VO2 max, reducing abdominal fat, and lowering blood sugar and HbA1c levels. The reasons for this are not fully understood.

• HIIT might activate AMPK and PGC-1α signaling pathways to a greater extent than MICT, potentially influencing metabolic health more significantly.

• Both HIIT and SIT lead to substantial glycogen breakdown during workouts, potentially contributing to their metabolic benefits.

Exercise and Abdominal Fat:

Exercise, even without weight loss, can effectively reduce abdominal fat, especially harmful visceral fat (VAT).

• High-intensity interval training (HIIT) seems to be more effective than moderate-intensity continuous training (MICT) for reducing VAT, while training duration doesn't significantly impact results.

• The exact mechanisms are unclear, but potential explanations include:

  • Increased sympathetic nervous system activity and lipolysis in VAT with higher exercise intensity.

  • Improved insulin sensitivity in VAT with HIIT compared to MICT.

  • Signaling through the cytokine IL-6, acting as an anti-inflammatory myokine, promotes fat burning.

  • Complex interactions between muscle and fat tissue, are influenced by cytokine type, concentration, and origin.

Moderate-to-high intensity exercise is linked to reduced inflammation markers like IL-6, resistin, and leptin, and increased anti-inflammatory adiponectin. However, exercise interventions without weight loss often show limited impact on these markers.

Studies suggest:

• Moderate-intensity exercise without weight loss may not improve markers of AT dysfunction, like adipocyte size.

• Exercise, even without weight loss, improves body composition by reducing fat mass and increasing muscle mass.

• Contracting muscles can potentially reduce visceral fat (VAT) through myokines like IL-6.

• Exercise improves insulin sensitivity in both muscle and fat tissues.

Overall:

• Exercise benefits metabolic health by improving insulin sensitivity, glucose metabolism, and oxidative phosphorylation, even if it doesn't directly reduce markers of AT dysfunction.

• More research is needed to understand the full impact of different exercise regimes on AT function and dysfunction markers.

Journal Reference

Kolnes, K. J., Petersen, M. H., Lien-Iversen, T., Højlund, K., & Jensen, J. (2021, September 24). Effect of Exercise Training on Fat Loss—Energetic Perspectives and the Role of Improved Adipose Tissue Function and Body Fat Distribution. Frontiers in Physiology, 12. https://doi.org/10.3389/fphys.2021.737709

Related

https://healthnewstrend.com/think-sharper-react-faster-why-you-need-exercise-for-your-brain

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