Effects of fasting intervention regulating anthropometric and metabolic parameters in subjects with overweight or obesity: a systematic review and meta-analysis.

This systematic review and meta-analysis investigated the effects of different fasting interventions on anthropometric (body measurements) and metabolic (blood markers) parameters in individuals who were overweight or obese.

The interventions included various forms of fasting:

• Periodic Fasting (PF): Fasting for 1 or 2 days per week, eating normally on other days.
• Intermittent Fasting (IF): This category included:
  • Complete Alternate-Day Fasting (CADF): Zero calorie intake on fasting days.
  • Alternate-Day Modified Fasting (ADMF): Consuming 20–25% of energy needs (typically 400–600 kcal) on fasting days.
  • Time-Restricted Feeding (TRF): Limiting daily food consumption to 8 hours or less (e.g., eating only between 12 PM and 8 PM).
• Very Low Calorie Diet (VLCD): Consuming 800 kcal or less per day.

The comparators (control groups) in the included studies typically involved either:

• A normal diet without specific restrictions.
• An energy restriction group (e.g., a continuous calorie-restricted diet).

The outcome measures assessed were:

• Anthropometric parameters:
  • Body weight (kg)
  • Body Mass Index (BMI, kg m−2)
  • Fat Free Mass (FFM, kg)
  • Fat Mass (FM, kg)
  • Waist Circumference (WC, cm)
• Metabolic parameters:
  • Total Cholesterol (TC, mmol L−1)
  • Low-Density Lipoprotein Cholesterol (LDL-C, mmol L−1)
  • High-Density Lipoprotein Cholesterol (HDL-C, mmol L−1)
  • Triglycerides (TG, mmol L−1)
  • Systolic Blood Pressure (SBP, mmHg)
  • Diastolic Blood Pressure (DBP, mmHg)
  • Blood Glucose (mmol L−1)
  • Insulin (mIU L−1)

The meta-analysis included a total of 25 randomized controlled trials (RCTs) involving 1358 participants who were classified as overweight or obese based on local criteria in each study.

Key characteristics of the study population, synthesized across the included trials:

• Sample Size per Study: Individual study sample sizes varied, with the smallest having 10 participants in the intervention group and 8 in the control group, and the largest having 76 in the intervention group and 51 in the control group.
• Age: The average age of participants across studies generally ranged from approximately 22 years to 65 years, with most studies focusing on adults in their 40s and 50s. For example, one study had an average age of 22.9 ± 4.1 years, while another had 64.7 ± 7.0 years.
• Gender: Most studies included a mix of men and women ("A(W + M)"). Some studies focused exclusively on women ("A(W)") or men ("A(M)"). For instance, one study had 15 men and 67 women in the intervention group, while another had 17 men and 0 women.
• Health Status: Participants were generally overweight or obese. The majority of studies excluded individuals with diabetes ("ND"), but a few studies specifically included participants with diabetes ("D"). For example, 4 studies included participants with diabetes, while 21 studies did not.
• Setting: The studies were conducted in various regions, including the US, Australia, Germany, Malaysia, UK, Japan, Finland, and Sweden, indicating a diverse geographical representation.

In summary, the meta-analysis synthesized data from a broad range of adult populations with overweight or obesity, including both men and women, across different age groups, and with varying diabetes statuses, reflecting a wide applicability of the findings to the general overweight/obese population.

The meta-analysis compiled data from various randomized controlled trials, and while the abstract does not detail the specific instruments used in each individual study, it implies standard clinical and anthropometric measurement techniques.

For anthropometric parameters, measurements would have typically involved:

• Body weight: Measured using calibrated scales, usually in kilograms (kg).
• Body Mass Index (BMI): Calculated from measured weight and height (weight in kg / (height in meters)^2). Height would have been measured using a stadiometer.
• Fat Free Mass (FFM) and Fat Mass (FM): These body composition measures are typically assessed using methods like Dual-energy X-ray Absorptiometry (DXA), bioelectrical impedance analysis (BIA), or air displacement plethysmography (e.g., Bod Pod). The specific method would vary by study.
• Waist Circumference (WC): Measured using a non-stretchable tape measure at a standardized anatomical landmark (e.g., at the narrowest point between the lower rib margin and the iliac crest, or at the level of the umbilicus).

For metabolic parameters, measurements would have involved standard clinical laboratory tests on blood samples:

• Total Cholesterol (TC), Low-Density Lipoprotein Cholesterol (LDL-C), High-Density Lipoprotein Cholesterol (HDL-C), and Triglycerides (TG): These lipid profiles are typically measured from fasting blood samples using automated clinical chemistry analyzers. Results are usually reported in millimoles per liter (mmol L−1).
• Blood Glucose: Measured from fasting blood samples, typically using enzymatic methods on clinical chemistry analyzers, reported in mmol L−1.
• Insulin: Measured from fasting blood samples, often using immunoassays (e.g., ELISA or chemiluminescence immunoassay), reported in milli-international units per liter (mIU L−1).
• Systolic Blood Pressure (SBP) and Diastolic Blood Pressure (DBP): Measured using a sphygmomanometer (manual or automated) after a period of rest, typically in a seated position. Results are reported in millimeters of mercury (mmHg).

The consistency and standardization of these measurements across the included studies are important for the validity of a meta-analysis, although the abstract does not provide details on inter-study measurement variability.

This study is a systematic review and meta-analysis, which is a high-level form of evidence synthesis.

Study Design Explained:

• Systematic Review: This involves a comprehensive and unbiased search for all relevant studies on a specific research question, followed by a critical appraisal and synthesis of their findings. The goal is to minimize bias and provide a reliable summary of existing evidence.
• Meta-analysis: This is a statistical technique used within a systematic review to combine the quantitative results from multiple independent studies. By pooling data, a meta-analysis can provide a more precise estimate of an intervention's effect and increase statistical power compared to individual studies.

Search Strategy and Data Retrieval:

• Databases Searched: The authors systematically searched four major scientific databases: PubMed, Cochrane Library, Web of Science, and EMBASE.
• Search Period: The search covered literature from the inception dates of these databases up to October 2019.
• Keywords: A comprehensive set of keywords was used to identify relevant studies, including "fasting," "very low calorie diet," "inter