Understanding Obesity and Energy Balance for Sustainable Weight Management

1. Obesity and Energy Balance

2. Key Skills Define obesity and body mass index (BMI), and explain the health consequences of obesity and underweight. Discuss contributing factors that have led to an increase in obesity in the U.S. Use the calories in/calories out model to explain how positive and negative energy balance lead to weight increase. Distinguish between hunger and appetite, and explain how various hormones affect these sensations. Discuss the metabolic set point hypothesis of obesity, and how it relates to both hunger and satiety, as well as the growth/division of fat cells. Understand factors that affect caloric input , and how we harvest energy from sugar and fat. Explain how multiple factors affect a persons calorie output, including their basal metabolic rate, the thermic effect of food, and their physical activity. Explain the major components of a sustainable weight maintenance program.

3. Comparing Weights Suppose one person weighs 175 pounds and another weighs 120 pounds. Is this enough information to tell whether either person is overweight? Does directly comparing the weights of two people tell you which one is fatter? What other information might help a doctor work out what a persons healthy weight is?

4. BMI Many factors determine a healthy weight, such as sex, age, ethnicity, and height. BMI takes height into account to estimate how heavy a person is for their size. BMI < 18.5 = underweight; BMI > 25 = overweight; BMI > 30 = obese BMI is not for making a diagnosis! Muscular athlete with compact frame may have BMI over 25 (overweight). (Img source: vertex42.com)

5. Underweight Being underweight (BMI < 19) can be dangerous, especially in age. Factors that cause underweight include genetics, eating disorders, depression, digestive problems, and thyroid conditions. As people get older, it becomes harder to heal if the body doesnt have some fat reserves. Especially in older women, being very thin can be associated with osteoporosis and brittle bones. (Img source: Medguidance.com)

6. Obesity in the US The rate of obesity in the United States has nearly tripled since the 1960s. Between 1980 and 2012, the percentage of adolescents (age 12- 19) who are obese increased from 5% to 21%! Even children as young as 6-11 years old are now showing obesity (18% of children in this age group in 2012). Hypothesize some factors that could be worsening this epidemic of obesity. (Img src: Centers for Disease Control)

7. Causes of Obesity Obesity is caused by caloric imbalance . The body takes in more dietary calories than it releases through exercise and body functions, and stores the excess energy by making fat. A simplified model: Calories in > calories out = Weight gain Calories in < calories out = Weight loss Be careful! Losing weight safely is NOT as simple as just reducing your caloric intake or increasing your caloric output with exercise. As well see, a combination of calorie in/calorie out/appetite-based approaches with healthy meals is needed to lose weight in a maintainable way! (Img credit: Centers for Disease Control)

8. Factors in the Obesity Epidemic Factors raising the Calorie Input of Americans: Soda and juice consumption. Snacking Bigger portion sizes Value-sized empty calories Advertising Fast food Factors lowering the Calorie Output of Americans: Limited time for exercise Sedentary lifestyle/jobs Increased use of TV and video games Lack of safe parks and walking areas

9. Portion Sizes The average portion sizes for a burger and fries have tripled since 1960. Large portion sizes have a psychological effect on appetite (the want to eat). People are more likely to overeat when more food is put in a container. Why have portion sizes increased so drastically, and how can consumers cope with this?

10. Hunger vs. Appetite Appetite is psychological and physiological. It determines how much you eat . Psychological: Portion size, food plating Physiological : Leptin, dopamine Hunger is physiological - it makes you feel like you need to eat something . Low blood sugar Metabolic set point hypothesis Satiety is the sense of fullness.

11. Metabolic Set Point One factor that affects both hunger and appetite is how much fat a person already has! Fat cells (adipocytes) make hormones that regulate satiety. When you lose fat, your body compensates to increase calories in and reduce calories out by making you hungrier. This is the metabolic set point hypothesis , and helps explain why its so hard to sustainably lose weight. The brain has a built in adipostat , which is like a thermostat for fat. Weight loss is possible, but it effectively requires you to reprogram your brain.

12. Fat Cell Hyperplasia vs. Hypertrophy When we make more fat in our bodies, fat cells need to either expand or divide to store it. Hypertrophy is when fat cells individually get larger to store more fat. This is the most common way fat grows in adults. The division of fat cells, which increases the number of fat cells, is called hyperplasia . This is especially common in childhood and adolescent obesity. These fat cells all secrete hormones and tend to set the metabolic set point towards more calorie storage. This is one reason why its harder to reverse obesity that begins early in life.

13. Caloric Input: Metabolism of Nutrients Last lecture, we discussed how the digestive system breaks starch, triglycerides, and proteins into sugars, fatty acids, and amino acids. But how does the body actually get usable energy (calories) from these macronutrients? There are three steps needed to harvest energy from sugar: glycolysis, the Krebs cycle (Citric acid cycle), and oxidative phosphorylation ( electron transport chain). These steps produce the main energy storage molecule of cells: adenosine triphosphate (ATP).

14. ATP ATP is used by most cell processes for energy. It consists of adenosine (part of DNA), and three phosphate groups. Breaking off one phosphate and bonding it to oxygen releases energy for use. Releasing that phosphate turns ATP into ADP (adenosine di phosphate). We need to eat and breathe to recharge ADP back to ATP.

15. Glycolysis: First Step in Glucose Metabolism Whoa! Thats a lot of steps! Can we simplify this a little?

16. Glycolysis: First Step in Glucose Metabolism Breaking down one glucose (6-carbon sugar) gives us two pyruvate (3-carbon) molecules, a little ATP, and some NADH. NADH is a carrier of high-energy electrons well use in a later step!

17. Pyruvate gets turned into acetyl CoA We lose one carbon from each pyruvate. This makes a little more NADH and releases carbon dioxide waste. Acetyl CoA can then go into the mitochondria , parts of the cell specialized for harvesting energy.

18. The Krebs Cycle (citric acid cycle) harvests energy from acetyl CoA The Krebs cycle gives us a little ATP, makes more NADH and FADH 2 (a different electron carrier), and finishes breaking down the sugar. At this point, glucose has been broken down into CO 2 . But what do we do with the NADH and FADH 2 ? Organisms that dont use oxygen perform fermentation to get rid of the extra NADH/FADH 2 . But we can use it more efficiently.

19. The Electron Transport Chain (oxidative phosphorylation) uses oxygen and NADH/FADH 2 to make ATP This step produces the most ATP. Oxygen is turned into water, and NADH is recycled for later use. We arent ready to fully understand what is happening here but well revisit it after weve studied electrolytes.

20. Glucose glycolysis Pyruvate Acetyl CoA Fat Beta oxidation A little ATP NADH Mitochondrion Krebs cycle CO 2 Some ATP NADH FADH 2 Electron transport chain Carbon chain processing is in red. Electron carriers in blue Lots of ATP Water Oxygen

21. Another Diagram (Same Pathway, without Fat)

22. Oxygen and Human Life While we can live for days without water and weeks without food (though its not recommended), we can only survive for minutes without oxygen. Given everything weve seen here so far Why is a constant supply of oxygen so critical for survival? Why do we die so quickly if we dont breathe?

23. Brain Oxygen Demand The brain uses 20% of the bodys oxygen, roughly, because it needs a huge amount of ATP . The cells that make up the brain, called neurons , need ATP to send messages back and forth. Without these messages, a person is brain- dead. When part of the brain loses oxygen because of lack of blood flow from a clot, a stroke results.

24. Calorie Output There are three major ways we spend and release energy, burning calories: 1. Basal metabolism (Resting Energy Expenditure): The energy we burn just to maintain our body temperature and keep us alive. 2. Physical activity: Exercise and daily movement. In addition, physical activity increases our Resting Energy Expenditure! 3. Digestion + Metabolism of Food: It takes energy to break down food and harvest energy from it. Some foods take more energy to break down than others. We call this the Thermic Effect of Food.

25. Resting Energy Expenditure Resting Energy Expenditure consists of the calories you burn even when you are not physically active or digesting food. Basal Metabolic Rate specifically refers to the REE after waking up in the morning. About 2/3rds of the calories you burn in a day are REE! Keeping your body warm takes a lot of energy. Having more muscle can increase REE. On the other hand, crash diets and heavy food restriction lower REE, making it harder to lose weight and maintaining the metabolic set point. Aging also decreases REE.

26. Physical Activity Regular physical activity, which raises REE, is better than occasional fits of exercise. As the diagram shows, it takes a long time for exercise alone to burn off calories! Physical activity

27. Digestion/Thermic Effect of Food About ten percent of the calories you eat are burned in the process of digestion. This is the Thermic Effect of Food . While it may be slightly higher for protein, research remains ambivalent on whether this effect is sufficient to explain weight loss on high-protein diets.

28. A Maintainable Diet A good diet is not one that a person uses for six months, then drops. Many dieters regain the lost weight! (The often-quoted figure of 95% of dieters regain lost weight may be too pessimistic, but the regain rate is high.) To avoid this, long-term lifestyle change is needed. If you eat fewer calories, you may feel less energetic. If you exercise more, you may feel hungrier. The only way to sustainably, safely lose weight is to eat healthily and exercise regularly in a way you can maintain.