Obesity Causes and Impacts

Obesity II

• This lecture examines the causes of obesity, specifically environmental (external, overeating and reduced activity) and genetic (internal) causes.
• The lecture also considers whether the obesity epidemic is over-hyped by scientists and drug companies.
• Lastly, it explores other correlates of rising obesity, such as smoking, delayed pregnancy, and psychoactive drugs.

The Causes of the Obesity Epidemic

• The primary cause of obesity is a simple imbalance of energy intake exceeding energy expenditure, primarily over the last four decades.
• Two key factors contributing to this imbalance:
  • The development of an obesogenic environment.
  • A preexisting genetic disposition to become obese.
• Importantly, a genetic disposition becomes significant within an obesogenic environment.

The Obesogenic Environment

• The obesogenic environment has developed over the last four decades.
• It is readily apparent in developed nations, particularly North America, Europe, and Australia.
• The environment is characterised by reduced physical activity and increased availability of processed foods.
• This environment is intimately connected to daily life.

Physical Activity

• Physical activity has decreased significantly in the last 40 years, particularly in Western nations.
• Growing use of cars, television viewing, and digital media consumption are contributors to this sedentary lifestyle choice.
• This reduces total daily energy expenditure.

Occupation

• Modern occupations have become less physically demanding.
• Work shifts from manufacturing and agriculture to service industries have contributed to this reduction of physical activity.
• Consequently, daily energy expenditure at work is lower than in the past.

Travel to Work

• In the U.S., less than 10% of journeys outside the home are made on foot or bicycle.
• Obesity rates tend to be higher in car-dependent areas lacking in walking and recreational opportunities.
• This reduces energy expenditure.

Leisure Activity

• Television viewing in Western cultures has increased, now exceeding 26 hours per week (including other devices).
• The amount of television viewing correlates with obesity rates.
• The consumption of processed food and high-fat-high-sugar snacks is also significantly associated with leisure activity and exposure to these products via advertising.

Variety and Portion Size

• The availability and variety of palatable foods have increased in supermarkets, significantly.
• This corresponds with an increase in portion sizes in many outlets.
• Larger portions contribute to increased food consumption.

Physical Activity - Cause or Correlation?

• The available evidence suggests an association between lower physical activity and higher obesity rates.
• However, longitudinal studies are closer to providing causal evidence.
• Evidence points to a conclusion that lower physical activity directly contributes to higher obesity rates.

Schools

• In the U.S. and other Western nations, schools have reduced physical education programs.
• School canteens and vending machines promote high-fat and high-sugar snacks.
• Similar trends have also been observed in other settings.

Demographic Shifts

• Families rely more on processed foods due to greater working hours.
• Processed foods are typically high in fat, sugar, and salt.
• Consumers have limited control over the ingredients.

Processed Foods

• Palatable processed foods are more likely to be consumed than bland alternatives.
• Processed foods often contain more sugar, salt, and fat.
• Effects such as high fat content and increased calorie intake of processed foods can lead to health issues.
• A positive correlation can be observed between consumption of processed foods, soft drinks, and obesity/related health conditions.

Variety

• Rats on cafeteria diets (a varied diet) become obese easily.
• Similarly, in humans, the abundant variety of palatable foods readily contributes to overeating.

Portion Size

• Portion sizes have risen significantly, particularly in the U.S.
• Larger portion sizes lead to increased consumption and higher caloric intakes.

Supersizing

• Supersizing is a common pricing/marketing strategy to increase profit.
• This strategy has led to increased consumption.
• It suggests that marketers make large portion sizes enticing and profitable, driving excessive consumption.

Is It Really the Environment?

• Increasing obesity rates occur within a relatively short timeframe for significant genetic changes.
• Thus, current evidence suggests that environmental influences are significant factors in determining obesity rates.
• Variations in lifestyle (i.e. diet and exercise), are strongly correlated with differences in obesity rates among similar populations.

The Environment and Genes

• Environmental factors are associated with more susceptible individuals, possibly through genetic pre-disposition to weight gain.
• However, some individuals remain thin regardless of the environment.
• This suggests there is an interplay of genetic and environmental factors in a complex interplay that influences weight gain.

Genetic Predisposition

• Genetic factors may influence factors such as energy balance, feeding behaviour, satiety regulation, fat cell numbers, and skeletal muscle growth.
• Obese individuals may initially have a higher number of fat cells.
• Genetic prediposition along with environmental factors significantly influence the risk of obesity.

Other Correlates of the Rise in Obesity

• Chemical pollutants have been linked to increased risk of obesity.
• The reduction in time spent sleeping correlates with increased obesity risk, possibly via hormonal changes.
• Smoking cessation correlates positively with weight gain.
• Maternal metabolic circumstances (famine, underweight, gestational diabetes) likely contribute to higher rates of obesity in their offspring.
• Newer research suggests other environmental factors are also contributors to obesity.

Conclusion

• Obesity is a complex phenomenon.
• Increased body weight can be predominantly attributed to overeating and reduced energy expenditure.
• Genetic predisposition and other factors such as environment, and chemical exposures also play an important role, indicating that much of this is still under investigation, potentially leading to other significant discoveries.