Dose-Response Effects of Exercise and Caloric Restriction on Visceral Adipose Tissue: A Systematic Review and Meta-Analysis

Table of Contents

Overall Summary

Overview

This systematic review and meta-analysis compared the effects of exercise and caloric restriction on visceral adipose tissue (VAT), a type of fat linked to heart disease and diabetes, in overweight and obese adults. Researchers analyzed data from 40 randomized controlled trials (considered the gold standard study design) involving 2190 participants. They investigated whether increasing the 'dose' of exercise or caloric restriction led to greater reductions in VAT, and they controlled for the weekly energy deficit (calories burned through exercise or not eaten) to compare the independent effects of each intervention. This is important because it helps us understand whether exercise or diet is better at targeting unhealthy VAT, specifically if doing more of one leads to bigger improvements.

Key Findings

Strengths

Areas for Improvement

Significant Elements

Figure 2

Description: This scatter plot illustrates the dose-response relationship between exercise and VAT reduction, showing that a larger calorie deficit through exercise leads to a proportionally greater decrease in VAT. Each point on the graph represents a study, and the downward-sloping line shows the overall trend.

Relevance: This figure visually demonstrates a key finding of the study: the dose-dependent effect of exercise on VAT reduction.

Figure 4

Description: This scatter plot shows the lack of a dose-response relationship between caloric restriction and VAT reduction. The relatively flat line indicates that reducing calories, while effective, doesn't necessarily lead to proportionally greater VAT loss depending on the size of the calorie deficit.

Relevance: This figure visually reinforces the surprising finding that the effect of caloric restriction on VAT isn't dose-dependent.

Conclusion

This meta-analysis provides strong evidence that exercise is a powerful tool for reducing visceral fat, particularly because increasing the amount of exercise leads to proportionally greater fat loss. While caloric restriction also reduces visceral fat, the amount of fat loss isn’t directly related to how many calories are restricted. The study emphasizes the importance of exercise in managing visceral fat, a major risk factor for chronic diseases. Future research should focus on exploring the impact of different exercise types on visceral fat and investigating why caloric restriction affects waist size but not VAT in a dose-dependent manner. Additionally, future studies should include a more balanced number of studies on exercise and caloric restriction to draw more robust conclusions about caloric restriction’s effects on VAT. These findings suggest exercise may be a preferred method to reduce health-risking visceral fat compared to calorie restriction, but incorporating both into a weight management program might provide the greatest overall benefit.

Section Analysis

Abstract

Overview

This systematic review and meta-analysis investigated the dose-response effects of exercise and caloric restriction on visceral adipose tissue (VAT) in overweight and obese adults. The researchers found that both exercise and caloric restriction reduced VAT, but only exercise showed a dose-dependent relationship, meaning more exercise led to greater VAT reduction. Caloric restriction's effect on VAT was not dependent on the size of the calorie deficit.

Key Aspects

Strengths

Suggestions for Improvement

Background

Overview

The background section establishes the context for the study by highlighting the growing prevalence of obesity and its link to various chronic diseases. It emphasizes the importance of visceral fat as a more significant cardiometabolic risk factor compared to BMI. The section also discusses existing obesity management guidelines that recommend exercise and caloric restriction, and points out the need for further research to determine their independent and dose-dependent effects on visceral fat reduction.

Key Aspects

Strengths

Suggestions for Improvement

Methods

Overview

This section details how the researchers conducted their study. They searched multiple databases (PubMed, Embase, CINAHL, and Web of Science) for relevant studies. They included randomized controlled trials that compared either exercise or caloric restriction to a control group that maintained their usual calorie intake, in overweight or obese adults. The main measurement they looked at was the change in visceral fat, measured by CT or MRI scans. They analyzed the data using meta-analyses and meta-regressions to determine the overall impact of each intervention and whether the effect was related to the size of the calorie deficit.

Key Aspects

Strengths

Suggestions for Improvement

Results

Overview

This section presents the findings of the study. The researchers analyzed data from 40 randomized controlled trials, totaling 2190 participants. Exercise was found to significantly reduce visceral fat, with a dose-response relationship observed. Caloric restriction also reduced visceral fat, but the effect was not dose-dependent. Both interventions led to a reduction in waist circumference, and this reduction was dose-dependent for both exercise and caloric restriction.

Key Aspects

Strengths

Suggestions for Improvement

Non-Text Elements

figure 1

This figure is a forest plot summarizing the effects of exercise on visceral fat across multiple studies. Each horizontal line represents a single study, with the square in the middle indicating the mean effect size for that study and the horizontal line extending to either side representing the confidence interval (a range of plausible values for the true effect). The size of the square is proportional to the weight of the study in the analysis (studies with larger sample sizes or less variability generally have more weight). The diamond at the bottom represents the overall combined effect size of all the studies, with its width representing the confidence interval for this combined effect. The vertical line at '0' represents no effect; if a study's confidence interval crosses this line, it means the effect of exercise in that study might not be statistically different from zero. The further a square is to the left of the '0' line, the greater the reduction in visceral fat with exercise in that study.

First Mention

Text: "Exercise significantly reduced visceral fat ((ES) −0.28 (−0.37 to −0.19); p<0.001; I2=25%) compared with controls (figure 1)."

Context: The results section is discussing the impact of exercise interventions on visceral fat.

Relevance: This figure visually summarizes the main finding regarding exercise and its impact on visceral fat across multiple studies, allowing for a quick assessment of the consistency and magnitude of the effect.

Critique
Visual Aspects
  • The labels on the y-axis (study names) are difficult to read due to the small font size.
  • The figure could benefit from a title directly on the plot itself.
  • Adding a brief explanation of how to interpret a forest plot directly on the figure would make it more accessible to a wider audience.
Analytical Aspects
  • While the overall effect size is provided, the units of measurement for visceral fat change are not clear from the figure itself.
  • The I² value, which indicates heterogeneity (variability) between studies, is provided in the caption but not explained visually in the figure.
  • It would be helpful to visually distinguish studies with statistically significant effects (those whose confidence intervals do not cross the zero line) from those that are not statistically significant.
Numeric Data
  • Overall Effect Size (ES): -0.28
  • 95% Confidence Interval for ES: [-0.37, -0.19]
  • I² (Heterogeneity): 25 %
  • p-value: 0.001
figure 2

This figure is a scatter plot showing the dose-response relationship between the weekly calorie deficit achieved through exercise and the change in visceral fat. Each point on the plot represents a single study. The x-axis represents the calorie deficit achieved through exercise, likely in calories per week. The y-axis represents the change in visceral fat, with negative values indicating a reduction in visceral fat. The line on the plot is a regression line, which shows the overall trend of the relationship between calorie deficit and visceral fat change. A downward sloping line indicates that as the calorie deficit increases, the reduction in visceral fat also tends to increase. The shaded area around the line likely represents a confidence interval or prediction interval, indicating the uncertainty associated with the regression line.

First Mention

Text: "Meta- regression demonstrated a dose–response effect of −0.15 ((−0.23 to −0.07); p<0.001) per 1000 calories deficit per week (figure 2)."

Context: The results section is reporting the dose-dependent effect of exercise on visceral fat reduction.

Relevance: This figure visually represents the dose-response relationship between exercise and visceral fat reduction, a key finding of the study. It shows whether increasing the 'dose' of exercise (calorie deficit) leads to a proportionally greater reduction in visceral fat.

Critique
Visual Aspects
  • The axis labels could be more descriptive, including the units of measurement (e.g., kcal/week for calorie deficit, cm³ or kg for visceral fat change).
  • The meaning of the shaded area around the regression line should be clarified in the caption or on the figure itself (e.g., 95% confidence interval).
  • The figure could benefit from a title directly on the plot itself.
Analytical Aspects
  • It would be helpful to indicate the statistical significance of the dose-response relationship visually on the plot (e.g., by adding a p-value or asterisk).
  • The figure could be improved by showing the individual data points for each study more clearly, perhaps by using different symbols or colors.
  • Consider adding a brief explanation of how to interpret a scatter plot and regression line directly on the figure or in the caption.
Numeric Data
  • Dose-response effect: -0.15
  • 95% Confidence Interval for dose-response effect: [-0.23, -0.07]
  • p-value: 0.001
figure 3

This figure is a forest plot summarizing the effects of caloric restriction on visceral fat across multiple studies. Each horizontal line represents a single study, with the square in the middle indicating the mean effect size of that study and the horizontal line extending to either side representing the 95% confidence interval. The size of the square is proportional to the weight of the study in the meta-analysis. The diamond at the bottom represents the overall pooled effect size of caloric restriction across all included studies and its confidence interval. A negative effect size indicates that caloric restriction reduced visceral fat compared to the control group.

First Mention

Text: "Caloric restriction significantly reduced visceral fat (ES −0.53 (−0.71 to −0.35); p<0.001; I2=33%) compared with controls (figure 3)."

Context: The authors are presenting the results of their meta-analysis on the effect of caloric restriction on visceral fat.

Relevance: This figure visually represents the main finding of the study regarding caloric restriction, showing that it leads to a statistically significant reduction in visceral fat. It allows readers to quickly grasp the magnitude and consistency of this effect across different studies.

Critique
Visual Aspects
  • The figure is clear and well-labeled.
  • The size of the squares appropriately reflects the weight of each study.
  • The overall effect size is clearly presented.
Analytical Aspects
  • The confidence intervals for individual studies and the overall effect are clearly shown.
  • The I² value is provided, indicating the degree of heterogeneity across studies.
  • The figure effectively communicates the key finding that caloric restriction reduces visceral fat.
Numeric Data
  • Overall Effect Size (ES): -0.53
  • 95% Confidence Interval for ES: [-0.71, -0.35]
  • I² (Heterogeneity): 33 %
  • p-value: 0.001
figure 4

This figure is a scatter plot showing the relationship between the weekly calorie deficit achieved through caloric restriction and the change in visceral fat. Each point on the plot represents a single study. The x-axis represents the calorie deficit, and the y-axis represents the effect size on visceral fat. The line represents the regression line, showing the overall trend of the relationship. If caloric restriction had a dose-response effect, we would expect to see a downward sloping line, indicating that larger calorie deficits lead to greater reductions in visceral fat. However, the line appears relatively flat, suggesting no clear dose-response relationship.

First Mention

Text: "Meta-regression showed that the effect of caloric restriction was not dose-dependent (ES 0.03 (−0.12 to 0.18); p=0.64) (figure 4)."

Context: The authors are discussing the results of their meta-regression analysis, which examined the dose-response relationship between caloric restriction and visceral fat reduction.

Relevance: This figure is crucial for understanding the nuanced findings of the study. While caloric restriction reduced visceral fat overall, this figure shows that the amount of reduction wasn't proportional to the size of the calorie deficit.

Critique
Visual Aspects
  • The figure is generally clear, but the axis labels could be more descriptive.
  • The units for the calorie deficit should be explicitly stated on the x-axis.
  • Adding a shaded area around the regression line to represent the confidence interval would improve interpretation.
Analytical Aspects
  • The figure effectively demonstrates the lack of a dose-response relationship.
  • The p-value for the meta-regression is provided, confirming the non-significance of the relationship.
  • The figure supports the conclusion that the effect of caloric restriction on visceral fat is not dose-dependent.
Numeric Data
  • Effect Size (ES) for dose-response: 0.03
  • 95% Confidence Interval for ES: [-0.12, 0.18]
  • p-value for dose-response: 0.64
table 1A, 1B

Tables 1A and 1B summarize the characteristics of the exercise and caloric restriction studies included in the meta-analysis, respectively. Table 1A describes the exercise interventions, including details like the study authors, year of publication, participant characteristics (age, BMI, waist circumference, any relevant comorbidities), the duration of the intervention, the groups involved (e.g., high-intensity interval training, moderate-intensity continuous training, control), the number of participants in each group (broken down by male/female), and the method used to measure visceral fat (MRI or CT). Table 1B provides the same information for the caloric restriction studies.

First Mention

Text: "A summary of the characteristics of the included studies is presented in table 1A,1B."

Context: The Results section describes the studies included in the meta-analysis, and refers to Tables 1A and 1B for a detailed overview of each study's characteristics.

Relevance: These tables are crucial for understanding the included studies and their characteristics. This information allows readers to assess the generalizability and applicability of the meta-analysis results. Knowing the specifics of each study helps evaluate the overall quality of the evidence.

Critique
Visual Aspects
  • The font size is too small, making it difficult to read the data.
  • The tables are dense and could benefit from more white space to improve readability.
  • Consider using shading or alternating row colors to enhance visual separation.
Analytical Aspects
  • While the tables provide a good amount of detail, they could benefit from a brief explanation of the abbreviations used in the table legend (e.g., NAFLD, T2DM).
  • It would be helpful to include a column indicating the calculated weekly energy deficit for each study, as this is a key variable in the meta-regression analysis.
  • Consider adding a column summarizing the main findings of each individual study (e.g., change in visceral fat) to allow for a quick overview.
Numeric Data
table 1 (A) characteristics of exercise studies and (B) characteristics of caloric restriction studies

This table, labeled as both 'Table 1A, 1B' and 'Table 1 (A) and (B)', provides detailed characteristics of the studies included in the meta-analysis. Part (A) focuses on exercise studies, while part (B) focuses on caloric restriction studies. For each study, the table lists information such as authors and year, presence of comorbidities in participants, average age and BMI, average waist circumference, study duration, the types of intervention groups (e.g., different exercise intensities, control groups), the number of participants broken down by sex, and the method used to measure visceral fat (MRI or CT). It uses many abbreviations, like NAFLD for non-alcoholic fatty liver disease, T2DM for type 2 diabetes mellitus, and HIIT for high-intensity interval training.

First Mention

Text: "A summary of the characteristics of the included studies is presented in table 1A,1B."

Context: This sentence, found in the Results section, introduces the table and its purpose within the study.

Relevance: This table is essential for understanding the characteristics of the individual studies included in the meta-analysis. It allows readers to assess the heterogeneity of the studies, understand the types of interventions used, and evaluate the overall quality of the evidence based on factors like sample size, participant characteristics, and study duration.

Critique
Visual Aspects
  • The font size is very small, making it challenging to read the data.
  • The table is dense and could benefit from more white space between rows and columns to improve readability.
  • Using alternating row colors or light shading could improve visual clarity.
Analytical Aspects
  • While the table is comprehensive, the numerous abbreviations (e.g., NAFLD, T2DM, HIIT) can be difficult to follow without constantly referring to the legend. Explaining some of these abbreviations directly in the table or providing more context could be helpful.
  • The table could benefit from a column explicitly stating the calculated weekly energy deficit for each study, as this is a central variable in the analysis.
  • Including a summary column indicating the direction and magnitude of the effect on visceral fat for each individual study would allow for a quicker grasp of the individual study results.
Numeric Data
table Table 1 Continued

This table, a continuation of Table 1 from the previous page, provides detailed characteristics of the caloric restriction studies included in the meta-analysis. Each row represents a single study and includes information about the study's authors and publication year, the presence of comorbidities in the studied population, the average age and BMI of participants, average waist circumference, the duration of the intervention, the groups involved (e.g., caloric restriction, control), the number of participants broken down by sex, and the method used to measure visceral fat (CT or MRI).

First Mention

Text: "A summary of the characteristics of the included studies is presented in table 1A,1B."

Context: The results section describes the characteristics of included studies and refers to Table 1A and 1B for a summary.

Relevance: This table is crucial for understanding the characteristics of the studies included in the meta-analysis, allowing readers to assess the generalizability and potential biases of the results. It provides context for interpreting the findings related to caloric restriction and its impact on visceral fat. It's like providing the ingredients list for a recipe - you need to know what went into the analysis to understand the final outcome.

Critique
Visual Aspects
  • The font size is small, making it difficult to read the data.
  • The use of numerous abbreviations (e.g., NAFLD, T2DM, CR, CON) could be challenging for readers unfamiliar with the field.
  • The table is split across two pages, which disrupts the flow of reading.
Analytical Aspects
  • While the table provides descriptive data, it doesn't offer any summary statistics (e.g., mean age across all studies, range of intervention durations) which could provide a clearer overview.
  • The table doesn't indicate which studies contributed data to the dose-response analysis, making it difficult to connect this table to Figure 4.
  • It's unclear why some studies were not included in the meta-analysis (indicated by '¶'). More explanation would be helpful.
Numeric Data
  • Number of studies: 22
  • Minimum intervention duration: 12 weeks
  • Maximum intervention duration: 50 weeks

Discussion

Overview

This study investigated the effects of exercise and caloric restriction on visceral fat in overweight and obese adults. Both methods reduced visceral fat, but only exercise showed a dose-response relationship (more exercise, more fat reduction). While both interventions reduced waist circumference, only caloric restriction showed a dose-dependent relationship for this outcome. This is the first meta-analysis to compare these interventions while controlling for weekly caloric deficit.

Key Aspects

Strengths

Suggestions for Improvement

Conclusions

Overview

This research supports the idea that exercise is an effective way to reduce visceral fat in overweight and obese adults, and that the more exercise you do (within the limits of the studies), the more visceral fat you lose. Caloric restriction also reduces visceral fat, but the amount of fat lost doesn't seem to be linked to how many calories are restricted. This might be because there were fewer studies on caloric restriction than on exercise. Interestingly, both exercise and caloric restriction reduced waist circumference, and this reduction was related to the amount of exercise or restriction.

Key Aspects

Strengths

Suggestions for Improvement

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