KIN 334: LECTURE 3 OBESITY (PG 31-78)

Understanding the Risks Associated with Obesity

• Various health conditions linked to obesity:

  • Diabetes: Obesity significantly increases the risk of developing Type 2 Diabetes.

  • Hypertension: Higher body weight can lead to increased blood pressure.

  • Metabolic Syndrome: A cluster of conditions that occur together, increasing the risk of heart disease, stroke, and diabetes.

  • Other Conditions: Includes osteoarthritis and certain types of cancer.

Understanding the Biological Mechanisms

• FFA (Free Fatty Acids): Elevated levels associated with obesity contribute to insulin resistance and other metabolic issues.

• Ectopic Fat: Defined as excess adipose tissue that is not classically associated with adipose tissue storage, often found in organs like the heart and kidney.

  • Significantly increases the risk of cardiometabolic diseases but is responsive to exercise.

• Insulin Resistance: A physiological condition where insulin becomes less effective at lowering blood glucose levels. Factors thought to contribute include:

  • FFA

  • Ectopic fat

  • Inflammation

  • Adipokines (Cytokines produced by adipose tissue)

  • Adiponectin: A hormone produced by adipose tissue; lower levels associated with obesity and insulin resistance.

• Adipocytes as Endocrine Cells: Adipose tissue is metabolically active and produces hormones that can lead to inflammation, increasing the risk of cardiovascular disease (CVD) and other diseases.

• Inflammation: Associated with chronic obesity, leading to various health risks.

Abdominal Obesity

• Individuals with the same BMI may have vastly different health risks based on the distribution of body fat.

  • Example:

  • A person with a BMI of 25 but excessive abdominal fat might have worse health outcomes than a person with a BMI of 30 and low abdominal fat.

  • Reference: Neeland 2019

Visceral Fat

• Definition: Refers to fat stored deep in the abdomen around internal organs, such as intestines and liver.

• Characteristics: Often associated with an "apple" shape or "beer belly."

  • Significant health risks increase with higher amounts of visceral fat; important to monitor as VAT is a key risk factor for obesity-related diseases.

  • Reference: Neeland 2019.

Obesity and Risk for Disease: Ectopic Fat

• Ectopic Fat: Associated with organs rather than traditional fat stores significantly increases the risk of several cardiometabolic diseases.

  • However, ectopic fat is responsive to exercise.

  • Reference: Tchernof, 2013.

Obesity and Risk for Disease: Insulin Resistance

• Insulin Resistance: Further defined as a condition where the hormone insulin fails to effectively lower blood glucose levels.

  • Potential mechanisms involved:

  • Free Fatty Acids (FFA)

  • Ectopic fat

  • Inflammation

  • Adipokines

  • Adiponectin

Adipocytes as Endocrine Cells

• Adipose tissue exhibits significant endocrine activity.

  • Sustained high levels of adipocytes lead to increased inflammation, elevating the risk of cardiovascular disease (CVD) and other health-related conditions.

• Reference: Grundy Nature Reviews Drug Discovery 5,295–306 (April 2006).

Summary

• Obesity is linked to various health conditions:

  • Some conditions are expected, like dyslipidemia and insulin resistance.

  • Some are less expected, like certain cancers.

• The relationship between obesity and health conditions is not always causal.

  • Causal mechanisms are partially understood but vary significantly.

  • Understanding these mechanisms can help inform treatment strategies.

Selected Factors Affecting Energy Balance

• Evaluated factors affecting energy balance in obesity include:

  • Sleep

  • Stress

  • Genetics

  • Epigenetics

  • Obesity in Youth

  • Critical Periods

Sleep and Obesity

• In 2004, approximately 30% of US adults reported usually sleeping 6 hours or less nightly, an increase from 20% in 1985 (CDC, 2005).

• Cross-Sectional/Longitudinal Evidence:

  • Data from the National Health and Nutrition Examination Survey (NHANES) indicated that sleep has been assessed since the 1980s.

Sleep and Obesity: Average BMI Data

• Average BMI and hours of sleep reported in different years:

  • Figure demonstrating average BMI by sleep hours (1982-1984):

  • Average BMI was noted among ~7000-9600 participants.

• Indications suggest that less than 7 hours of sleep correlates with a higher BMI. Some studies report a U-shaped curve showing higher BMI at both ends of the sleep duration spectrum (below 7 hours and over 9 hours).

Experimental Evidence Related to Sleep Deprivation

• Findings from Experimental Studies:

  • Sleep deprivation is shown to increase food intake in both rats and humans.

• Data indicating appetite ratings after two days of sleep restriction across various food categories:

  • Food Categories:

  • Sweets (increased appetite by 33%)

  • Salty foods (increased by 45%)

  • Starchy food (increased by 33%)

  • Fruits (increased by 17%)

  • Vegetables (increased by 21%)

  • Meat (increased by 21%)

  • Dairy (increased by 23%)

  • Reference: Spiegel, 2004.

Biological Mechanisms of Sleep and Appetite

• Leptin and Ghrelin:

  • When sleep is restricted, leptin levels decrease by 18%, while ghrelin levels increase by 28%.

  • Increased levels of hunger and overall appetite were noted (24% and 23% respectively).

Stress and Obesity

• Cortisol: Known as the stress hormone with both short-term benefits and long-term detriments.

  • Primary function includes contributing to insulin resistance.

Relationship Between Stress and Obesity

• Emotional and psychological stress impacts weight:

  • Approximately 40% gain weight under chronic stress.

  • Reference: Dallman, 2010.

• Cushing’s Syndrome: Excess cortisol production and its effects on metabolism.

Experimental Evidence for Stress Effects

• Research conducted on premenopausal women showed the impact of mental stress on food intake.

  • High cortisol levels correlated with increased calorie consumption, specifically for high carbohydrate and sweet foods.

  • Reference: Epel 2001.

Implications for Practice

• Various eating behaviors related to obesity include:

  • Restrained eating,

  • Night-eating syndrome,

  • Binge eating syndrome,

  • Emotional eating, smoking, and alcohol consumption.

  • The use of food or physical activity diaries may prove beneficial.

Genetics and Epigenetics

• Investigation into whether biological predisposition or inherited factors contribute to obesity:

  • Assortative Mating:

  • Lean individuals tend to mate with lean individuals; obese individuals mate with other obese individuals.

  • Example: A 16% chance for offspring obesity if both parents are obese.

Quebec 100-Day Overfeeding Experiment

• Conducted on 12 pairs of male MZ twins, mean age 21.

  • Overfeeding protocol involved 1000 kcal surplus per day for 100 days, leading to significant weight and fat increases.

  • Body weight gain of 8 kg and large increases in fat mass were noted, leading to implications about dietary impacts on twin studies.

Body Weight Changes Response to Negative Energy Balance

• In a separate experiment, changes in body weight between twins in response to severe caloric deficits showcased significant variation, emphasizing the role of genetics in obesity susceptibility.

Obesity in Youth

• Definition and Classification:

  • Most obesity classifications now utilize BMI defined by percentile cut-offs based on CDC growth charts.

Critical Periods in Childhood Obesity

• Emphasis on experiences during prenatal and infancy stages: Birth weight, breastfeeding, exposure to maternal smoking, etc.

• Research indicates potential long-term impacts of these early life factors on BMI and obesity risk.

Conclusion

• Understanding factors contributing to obesity, including genetics, sleep, and stress, offers potential avenues for intervention and prevention strategies. The interplay of these factors highlights the complexity and multifactorial nature of obesity as a public health challenge.