Obesity, a condition characterized by excessive fat accumulation, poses a significant global health challenge. While body mass index (BMI) is a commonly used measurement, it has limitations, especially in individuals with disabilities. Understanding the multifaceted nature of obesity, its measurement, causes, and consequences is crucial for effective management and prevention.
Defining and Measuring Obesity
Obesity is medically defined as the excessive accumulation and storage of fat in the body, leading to organ-specific consequences. Traditionally, obesity is assessed using body mass index (BMI), calculated as weight in kilograms divided by the square of height in meters. While BMI is convenient, it doesn't account for body composition or fat distribution, making it less accurate in certain populations, particularly those with disabilities. Review studies have shown that the commonly used BMI cutoff values have a low sensitivity to detect adipose tissue, and may have significant accuracy issues in disease and disability states. BMI does not take into consideration the differences in body composition, especially the percentage of body fat (%BF), which defines obesity. BMI also does not take into consideration the sites of fat accumulation, whether subcutaneous or visceral. Visceral fat, which encases organs such as the liver, heart, and bowel, is strongly associated with the organ-specific consequences characteristic of obesity.
Alternative Measurement Methods
To overcome the limitations of BMI, other methods can be used to measure body fat and assess obesity:
- Waist circumference: An easy and inexpensive measure that correlates with body fat, especially visceral fat.
- Waist-to-hip ratio: Another inexpensive measure that predicts disease development and mortality.
- Waist-to-height ratio: More accurate than BMI in predicting percentage body fat and differentiating between whole body and abdominal obesity.
- Skinfold thickness: Convenient and inexpensive, but requires training and may be difficult to measure in individuals with high BMI.
- Bioelectric impedance analysis (BIA): Convenient and relatively inexpensive, but accuracy can be affected by hydration status and illness.
- Underwater weighing (densitometry): Accurate but requires special equipment and water submersion.
- Air-displacement plethysmography: Accurate, safe, and comfortable, but expensive and not widely available.
- Dilution method (hydrometry): Accurate and relatively low cost, but requires special equipment and can be affected by hydration status.
- Dual Energy X-ray Absorptiometry (DEXA): Accurate and available at medical centers, but expensive and not suitable for pregnant women or individuals with very high BMI.
- MRI: Measures visceral fat and provides detailed information about tissue composition, but is expensive and time-consuming.
- CT: Measures visceral fat but involves radiation exposure.
BMI Weight Categories
Despite its limitations, BMI remains a useful tool for categorizing weight status:
Adults:
- Underweight: BMI < 18.5 kg/m²
- Normal weight: BMI 18.5-24.9 kg/m²
- Overweight: BMI 25.0-29.9 kg/m²
- Obesity: BMI ≥ 30.0 kg/m²
- Class 1 (Mild obesity): BMI 30.0-34.9 kg/m²
- Class 2 (Moderate obesity): BMI 35.0-39.9 kg/m²
- Class 3 (Severe obesity): BMI ≥ 40.0 kg/m²
Children (2-19 years):
- Healthy weight: BMI between the 5th and <85th percentiles
- Overweight: BMI between the 85th and <95th percentiles
- Obesity: BMI ≥ 95th percentile
The Etiology of Obesity
Obesity is a complex condition with multiple contributing factors. While an absolute etiology remains unknown, key contributors include increased caloric intake relative to activity level, genetic predisposition, and other underlying causes. Caloric balance is essential for maintaining a healthy weight; when calorie consumption exceeds energy expenditure, weight gain occurs. Reduced energy expenditure may be more important than increased food intake in causing obesity. Limited activity is a common occurrence in people with many causes for disability. Any alteration to the hypothalamus and arcuate nuclei can affect appetite, satiety, and metabolic rate. Possible genetic risk factors include melanocortin 4 receptor (MC4R) mutation, fat mass and obesity association gene (FTO), and insulin induced gene 2 (INSIG2).
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Hormonal Influences
Leptin and ghrelin are two hormones that significantly influence energy balance. Leptin regulates long-term energy balance by suppressing food intake and promoting weight loss. Ghrelin, a fast-acting hormone, stimulates appetite and promotes a positive energy balance, potentially leading to weight gain. Serum Ghrelin levels increase during fasting and surge shortly before meals. Leptin levels increase with overeating, reflecting adipose tissue proportion, whereas ghrelin levels rise during fasting and before meals.
The Role of Fat Distribution
The distribution of fat, particularly visceral versus subcutaneous fat, also plays a crucial role. Obese patients with visceral fat distribution exhibit greater abnormalities in glucose and lipid metabolism compared to those with subcutaneous fat distribution. This leads to a higher prevalence of insulin resistance, type 2 diabetes mellitus, hypertension, and coronary artery disease in individuals with visceral adiposity. This pattern frequently exists in certain disability populations (e.g., spinal cord injury, spina bifida, cerebral palsy). Therefore, insulin resistant diabetes should be recognized in these populations.
Genetic Predisposition
While physiological and lifestyle factors play a role, genetics also contribute to obesity. Twin, family, and adoption studies suggest a heritability rate of 40-70% for obesity.
Epidemiology and Risk Factors
The global prevalence of obesity has increased dramatically in recent decades. Between 1990 and 2021, obesity rates increased by 155.1% among males and 104.9% among females worldwide. This upward trend is projected to continue; by 2050, the number of adults classified as overweight or obese is expected to reach 3.8 billion-accounting for more than half of the global adult population. Obesity is a global public health concern; however, its prevalence is particularly pronounced in the United States. adults-approximately 76 million individuals-were classified as obese. By contrast, in 2015, Vietnam reported the lowest national obesity prevalence at just 1.6%, underscoring stark international disparities in obesity rates.
Challenges for People with Disabilities
People with disabilities face unique challenges in preventing obesity, including difficulty accessing healthy foods, side effects of certain pain medications, reduced ability to exercise, decreased energy, lack of accessible environments and resources.
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Mortality Risk
Obesity, defined as a body mass index (BMI) ≥ 30, is associated with increased all-cause mortality. Epidemiological data indicate a hazard ratio (HR) of 1.18 for obese individuals compared to their non-obese counterparts, signifying an 18% higher risk of mortality.
Risk Factors
Several factors contribute to the risk of obesity in adults:
- Genetic predisposition
- Diabetes mellitus
- Seasonal affective disorder
- Childhood physical abuse
- Shorter sleep duration (<5 hrs. in adults <60 years old)
- Excess pregnancy weight gain with failure to lose weight by 6 months post-partum
- Obesity in social network
- Pre-existing disability that limits mobility (e.g., spinal cord injury), including progressive disabilities (e.g., multiple sclerosis)
- Subacute medical conditions that cause limited mobility, that may not be permanent (e.g., post trauma with multiple fractures)
- Lower socioeconomic status
Risk factors for childhood and adolescent obesity include:
- Obesity in older siblings
- Increased birth weight
- Infants with higher BMI or rapid growth rates in infancy
- Television more than 8 hours per week at 3 years of age
- Parental obesity, especially maternal
- Lower parental educational attainment
- Lower self esteem
- Pre-existing disability or conditions that limits mobility (e.g., spina bifida, cerebral palsy), progressive conditions (e.g., muscular dystrophy), and other conditions associated with weight gain (e.g., Prader-Willi, Down Syndrome)
- Lower socioeconomic status
Medical issues that can contribute to obesity:
- Neuroendocrine disorders (metabolic syndrome, hypothyroidism, Cushing’s syndrome, hypothalamic obesity, polycystic ovary syndrome, growth hormone deficiency, hypogonadism)
- Medication-induced weight gain (corticosteroids, antidepressants, antipsychotics, antiepileptics, diabetic medications)
Lifestyle factors:
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- Fast food consumption
- Sedentary behaviors
- Excessive alcohol consumption
Disease Progression and Natural History
Critical periods in development, particularly during childhood, can influence an individual's predisposition to obesity and metabolic disease. High maternal BMI and excessive gestational weight gain are risk factors for childhood obesity. The period between the ages of 3 and 10 years is important in terms of predicting future overweight status. Moreover, the risk of being overweight in adulthood is at least twice as great for overweight children as for non-overweight children. This risk is 3 to 10 times higher if the child’s weight is above the 95th percentile for his or her age. Parental overweight also plays a strong role in this group. Nearly 75% of overweight children age 3 to 10 years remained overweight in early adulthood if they had one or more overweight parent, compared with 25% to 50% if neither parent was overweight.
Obesity in middle age is associated with increased risk of hospitalization and mortality after age 65. These hospitalizations and deaths are from coronary artery disease, cardiovascular disease and/or diabetes.
For people with disability, increasing weight is often associated with decreasing activity as a factor of growth and maturation (for childhood-onset disability types), directly related to the new onset of disability (temporary or permanent), or with decreasing activity over the course of chronic disability.
Consequences and Complications of Obesity
Obesity significantly increases the risk of various health problems:
- All-causes of death
- Hypertension
- Dyslipidemia
- Diabetes mellitus type 2
- Coronary heart disease
- Stroke
- Gallbladder disease
- Osteoarthritis
- Sleep apnea and breathing problems
- Some cancers (endometrial, breast, colon kidney, gallbladder, liver)
- Low quality of life
- Mental illness such as clinical depression, anxiety, and other mental disorders
- Body pain and difficulty with physical functioning
There may be an association with:
- Slipped capital femoral epiphysis in pediatric obesity
- Lateral femoral cutaneous neuropathy
- Carpal tunnel syndrome
With rapid weight loss, there may be increased risk of:
- Peroneal neuropathy
- Superior mesenteric artery syndrome
Assessment and History
Primary care physicians often take the lead in weight management, but all physicians, including physiatrists, play a role. Physiatrists may take a joint or primary role in management. Weight status may be a component of the referral for mobility issues or pain management, and many physiatrists take a primary role in health management for people with disability. General recommendations for weight management are for screening and evaluation first and foremost.
Screening Recommendations
- All adults without chronic disability and disease states: determine overweight/obesity using BMI (≥ 25 kg/m2) calculated from actual measures, and/or WC following standards (≥ 35 in/88 cm for women; ≥ 40 in/104 cm for men).
- Children and adolescents without longstanding disability and disease states: routine measured height/weight should be plotted, BMI calculated.
- People with disability: BMI/WC may be used with recognition of limitations; recognize possible sarcopenic component; use of other measures based on disability type (see Table above).
History Taking
A thorough history should include:
- History of present illness: Discuss the factors contributing to and associated with obesity-weight gain over time, age/gender (increasing age, hormonal changes), dyspnea, joint pain
- Medication history: Steroids, anti-epileptics, antidepressants, antipsychotics
- Sleep history: Daytime sleepiness, sleep apnea
- Past medical history: Diabetes, thyroid conditions, childhood obesity, level of disability
- Mood disorders: Depression/anxiety, eating disorders (binging, bulimia, night-eating)
- Family history: Obesity, diabetes, family lifestyle (e.g., eating habits, activity)
- Lifestyle and social history: Lifestyle events related to weight changes (e.g., change in marital status, new job, smoking cessation, level of physical activity, family…)
Weight Watchers and the Truth About Weight Loss
Weight Watchers, a well-known weight loss program, has evolved its approach to address the complexities of weight management. Rather than promoting unrealistic promises of quick and easy weight loss, Weight Watchers aims to provide a more honest and supportive environment. The One Show, a prestigious advertising and design award show, recognized Weight Watchers for its commitment to portraying the ups and downs, the struggles, and the realities of the weight loss journey. The campaign aimed to break away from the "garbage category" of before/after photos and celebrity endorsements, and instead, focus on the complicated relationship people have with their bodies and what success truly looks like.