Week 2: Overweight and Obesity

Subcutaneous Adiposity

• Visceral fat lies deep within the body cavities, surrounding internal organs including the liver, pancreas, and intestines
• Visceral fat can be stored within the liver and lead to non-alcoholic fatty liver disease (NAFLD)
• Visceral fat accumulation is associated with a higher cardiometabolic risk than subcutaneous fat due to its metabolic characteristics, which include insulin resistance and glucose intolerance

Visceral vs. Subcutaneous Adiposity

• Visceral fat is best measured by MRI, U/S, or CT
• A more practical measure is sagittal diameter
• Sagittal diameter is the distance from the floor/plinth to a horizontal level at the anterior abdomen at the level of the iliac crest, taken during a normal exhalation (tidal breathing)
• A sagittal diameter > 30cm is related to an increase in cardiovascular disease risk and insulin resistance

Overweight and Obesity

• Overweight and obesity are associated with an increased rate of death from all causes, particularly from cardiovascular disease
• Obesity and sedentary lifestyle are considered the second leading cause of preventable death in the USA and may overtake tobacco abuse within the next decade
• For obese individuals, life expectancy decreases by about 7 years compared with normal-weight individuals

Overweight and Obesity in Australia

• In Australia, per capita spending is approximately $830 more for an obese individual versus someone of normal body weight
• Obesity reduces life expectancy, and this effect is more powerful in those who develop obesity earlier in life

Pathophysiology of Obesity

• Obesity results from longstanding positive energy balance
• Average daily calorie intake has increased by over 200 kcal over the last several decades as food costs have fallen dramatically and as more calories are consumed outside the home
• At the same time, physical activity has fallen because of advances in equipment and ergonomics in the workplace

Clinical Considerations in Overweight and Obesity

• Medical causes of obesity, including illnesses, medications, and lifestyle changes known to increase weight, should be identified
• Establishing where the patient is located on the Stages of Change Model can be useful in helping to approach and commence a treatment plan
• Readiness to change (i.e., to lose weight) should be used to develop a tailored plan for the individual### Pathophysiology of Obesity
• Obesity results from longstanding positive energy balance.
• Average daily calorie intake has increased by over 200 kcal over the last several decades due to decreased food costs and increased consumption outside the home.
• Physical activity has fallen due to advances in equipment and ergonomics in the workplace.
• Genetic and physiologic factors, including neurological and peripheral endocrine messengers, influence food intake and nutrient utilization, making weight loss efforts challenging.
• Advanced neuroimaging research has shown similar patterns of brain activation between addictive-like eating and substance abuse.
• Leptin, secreted by fat cells, is produced in proportion to weight and girth, but exogenous leptin administration has limited benefit for weight reduction.
• Genetic causes of obesity are rare, but a factor in at least half of human obesity, and body fat distribution is also genetically determined and gender-specific.

Clinical Considerations in Overweight and Obesity

• Medically significant obesity exists in most patients, but only a minority present requesting medical help with weight reduction.
• Compassion and understanding, coupled with flexible and practical weight loss recommendations, are essential for building rapport with obese patients.
• Most individuals seeking professional help with weight loss have a BMI of 38 or more and have attempted to lose weight several times in the past.
• Proper assessment of the barriers to, and benefits of, weight loss should be the initial step in the clinical evaluation of the obese patient.

Exercise Testing

• Exercise testing is performed to assess for the presence of coronary artery disease, determine functional capacity, and develop an exercise prescription based on heart rate.
• Seated devices, such as upper body ergometers, stationary cycles, or recumbent stepping machines, offer alternatives for patients who are unable to perform weight-bearing exercises.
• A low-level protocol with small increments (e.g., 0.5-1.0 MET) may be preferred for patients with a low peak exercise capacity.

Medical Management Summary

• A deficit of 7,700 kcal is needed to lose 1kg, so a typical diet can yield about 0.5kg of weight loss per week.
• Low-fat diets are recommended due to the high calorie content of fat and the heart health benefits for cholesterol lowering.
• Higher-protein and lower-carbohydrate diets have been favored by patients due to greater weight losses and better satiety.

Surgical Therapy

• Surgical procedures, such as laparoscopic techniques, can cause patients to lose one-third of their weight (>50% of their excess weight) within 18 months.
• Research has confirmed improved mortality rates with weight loss surgery, but there are significant risks (up to 1% for death and 15% for morbidity).
• Patients undergoing bariatric surgery must commit to a lifelong program of restricted diet, lifestyle changes, vitamin supplementation, and follow-up testing to ensure safety.

Exercise Prescription

• Exercise for weight gain prevention requires 150-200 minutes/week (1,200-2,000 kcal/week).
• Exercise alone for weight loss requires high amounts of total caloric expenditure, likely in the range of >3,000 kcal/week (225-420 minutes/week).
• Exercise and caloric reduction for weight loss can increase the weekly rate of weight loss by approximately 1kg over caloric reduction alone.
• Regular exercise of 60-90 minutes on most days of the week is generally recommended for long-term weight loss maintenance.

Cardiorespiratory Exercise

• Initially, exercise and physical activity should focus on cardiorespiratory (aerobic) modes, as they are linked to reductions in body mass.
• Resistance training may provide added benefits, particularly with respect to body composition, but the caloric expenditure of resistance training is less than that of aerobic exercise.