Individuals carrying excess weight often face a heightened risk of developing a spectrum of physical and mental health conditions. Interventions designed to facilitate weight loss are recognized as a means to improve overall health, with a weight reduction of five to ten percent of initial body weight frequently cited as a clinically significant target for enhancing health outcomes. However, the potential advantages of achieving a lower level of weight loss, specifically less than five percent of body weight, have not been as extensively studied or well-understood. This article seeks to explore and synthesize the existing evidence regarding the health benefits associated with losing less than five percent of body weight.
The Significance of Even Small Weight Reductions
While guidelines often emphasize the importance of achieving a five to ten percent weight loss for clinically meaningful improvements, the reality is that many individuals find it challenging to reach this threshold, especially within the timeframe of a typical 12-week lifestyle intervention. The implications of achieving a body weight reduction of less than five percent are often poorly understood. Interventions resulting in less than five percent weight loss are often deemed ineffective; however, they may still offer benefits in improving health outcomes, particularly for individuals living with obesity. This raises an important question: can losing a seemingly small amount of weight still lead to tangible health benefits?
Methodology and Scope of Research
To address this question, a comprehensive systematic review was conducted, encompassing a wide range of studies that assessed the impact of weight loss interventions resulting in less than five percent body weight reduction. Seven academic databases were searched, with no restrictions on language, country, or publication date, to ensure a broad and inclusive analysis. Studies were included if they were randomised or quasi-randomised controlled trials (RCTs) or intervention studies with pre-post measures. The included exposures were weight loss interventions with lifestyle (physical activity/diet) or pharmacological components. The participant criteria were adults (18 years or older) who lost less than five percent of their body weight following an intervention. Included outcomes were any type of health measures, including physical, mental, or behavioural. The health measures of interest were broad, and searches were structured without outcome terms to ensure all relevant outcomes were captured. Findings were required to be stratified by percentage weight loss. Studies from any country, language or published at any time were included. The review focused on identifying any measured physical or mental health markers or indices that showed improvement as a result of this modest weight loss. A total of 70 studies from 68 articles met the inclusion criteria, with participant numbers ranging from 14 to 10,742.
Diverse Health Markers and Indices Assessed
Across the included studies, a total of 137 distinct health markers were evaluated and subsequently categorized into several key areas:
- Metabolic Markers (n = 42): These included measures such as fasting plasma glucose (FPG), fasting insulin, Homoeostatic Model Assessment of Insulin Resistance (HOMA-IR), haemoglobin A1c (HbA1c), and adiponectin (APN).
- Cardiovascular Markers (n = 32): This category encompassed total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), systolic and diastolic blood pressure (BP).
- Anthropometric Measures (n = 19): These included waist circumference, body fat percentage, hip circumference, and body mass.
- Quality of Life Indices (n = 10): Standardized measures of sleep duration and quality, mood, asthma-related quality of life, the impact of weight on quality of life, and overall well-being were assessed.
- Inflammatory Biomarkers (n = 10): Various markers of inflammation within the body were examined.
- Renal and Hepatic Markers (n = 9): Measures related to kidney and liver function were included.
- Psychosocial and Behavioural Measures (n = 8): Aspects such as self-esteem, stress levels, and eating behaviours were considered.
- Pulmonary Function (n = 3): Measures of lung function were assessed.
- Total Mortality (n = 2): Data on overall mortality rates were included where available.
- Ovulatory Function (n = 1): Measures related to ovulation were assessed in relevant studies.
- Muscle Strength (n = 1): Assessments of muscle strength were included where available.
Overall Trends in Health Improvements
The analysis of the included studies revealed a predominantly positive trend, with 60% of studies reporting improvements in at least one health marker or index. Specifically, based on the available data, 87% of participants (n = 15,839) in the studies reported improvements in health markers or indices as a result of low-level weight loss. Approximately 37% of studies showed no change or mixed results, while only 3% observed a worsening of health markers or indices. This suggests that even a small amount of weight loss can have a beneficial impact on overall health.
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Specific Health Categories and Their Responses to Modest Weight Loss
Metabolic Markers
Metabolic markers were reported in 42 studies. Sub-sample sizes were reported for 37 of the 42 studies, with a total of 9389 participants. 22 studies (52%; n = 7980) demonstrated improvements, 13 studies (31%; n = 1006 participants) showed mixed results, while four studies (10%; n = 334*) indicated no change and three studies (7%; n = 69) indicated a worsening of outcomes or indices. A robust example is a 12-month RCT, with a sample size of 2161, that assessed the impact of weight loss on various metabolic markers and found mixed results. Within the <3% weight loss group there was a non-significant decrease in FPG, 2-h glucose, insulin, and HOMA-IR for both men and women; and non-significant decrease in A1C among men only.
Cardiovascular Markers
Cardiovascular markers were reported in 32 studies (n = 13,139). Among these studies, 18 (56%; n = 11,233) found overall improvements, eight (25%; n = 1362) presented mixed results, while five (16%; n = 519*) indicated no change, and one (3%; n = 25) showed a worsening of health markers and indices. Some studies disaggregated results further, a robust and high-quality 6-week RCT investigating (n = 4198) the impact of weight loss on blood pressure gave mixed results for those losing between 0% and 2.5% and those losing 2.5% and 5% body weight. In the 2.5-5% weight loss group there was a significant decrease in both systolic BP and diastolic BP for all patients.
Anthropometric Markers
Anthropometric markers were assessed in 19 studies, with a total of 5004 participants. Waist circumference (n = 15) was the most frequently reported marker, and included markers such as body fat percentage, hip circumference, and mass (kg).
Quality of Life Indices
Quality of life indices were assessed in 10 studies, with a total of 1222 participants. The most common indices were standardised measures of sleep duration and quality (Pittsburgh Sleep Quality Index), mood (Patient Health Questionnaire-8), asthma-related quality of life (Asthma Quality of Life Questionnaire), impact of weight on quality of life (IWQOL-Lite) and EQ-5D scores (EuroQol-5 Dimension scores).
Inflammatory Biomarkers
Inflammatory biomarkers were assessed in 10 studies.
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Limitations and Considerations
It is important to acknowledge certain limitations in the available data. The studies included in this review exhibited considerable heterogeneity in terms of study design, intervention types, and outcome measures. Additionally, the reporting of data was often inconsistent, with some studies stratifying outcomes by different weight-loss groups and others reporting overall baseline values or follow-up outcomes only by weight-loss groups. These factors made it challenging to conduct a meta-analysis and quantitatively synthesize the findings across all studies.
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