obesity epidemiology perspective

public health

why do humans tend to gain weight easily, but struggle to lose it ?

consider:

• biology (evolution, metabolism)

• environment (food access, marketing)

• social factors (work schedules, stress)

• technology and lifestyle

energy intake

Typically measure food intake in grams and energy intake in kilocalories

Kilocalorie is amount of energy needed to raise 1L or water 1 degree Celsius

U.S. government states that the average man needs 2,700 kcal / day and the average woman needs 2,200 kcal / day.

Needs vary considerably by body size (esp. lean body mass), physical activity level, and age (metabolism)

• food intake

• proteins, complex carbohydrates, triglycerides

• amino acids, glucose, glycerol and fatty acids

• protein synthesis, energy production, lipid synthesis and storage

energy yielding pathways

big picture: all three micronutrients can be broken down into ATP

Simple theory of energy metabolism (Incorrect and incomplete)

• Increase food intake over energy expenditure yields weight gain

• Decrease food intake below energy expenditure yields weight loss

• This theory fails to recognize endocrine regulation of body lipid
  stores and behavioral processes (appetite control) that vary with
  food intake, glucose homeostasis, and lipid metabolism.

Animals store fat in part because energy intake is discontinuous, while energy expenditure is always happening. Most vertebrate animals cannot feed continuously because they
have been selected by evolution to do lots of other vital things for survival and reproduction

Systems evolved, therefore, to enable animals to harvest food from the environment at a much faster rate than it is used, to give time for these other essential activities.

set point theory: energy balance . how the body attempts to regulate its weight

• neutral energy balance

• positive energy balance

• negative energy balance

neutral energy balance

no change in energy stores to maintain balance

positive energy balance

Increase in body weight. Growth, muscle mass, fat mass. But…In oxidation of
energy stores to maintain balance (use body stores as fuel)

negative energy balance

Body burns more calories than It consumes. Weight loss, fat mass, muscle mass, illness, dieting, etc. But…decrease in oxidation of energy stores to maintain balance (preserve body stores)

set point theorey

• body resists weight loss and weight gain

• upregulates energy expenditure if overheat

• downregulates energy expenditure if undereat

might have to look at the graphs in the slides in detail

processes of globalization that are critical to the nutrition transition

• liberalization of foreign direct investment

• FDI in developing countries increased 6 fold from 1990-2000, faster than the GDP or trade

• now the largest source of external financing for developing countries

case study: Mexico

• NAFTA (1994) liberalized foreign investment

• between 1995 and 2003, sales of processed foods (ex: soft drinks, snacks, baked goods) expanded by 5-10% per year

refer to in class notes as well !