Harvard University Initiative for Global Health Global Health Challenges Social Analysis 76: Lecture 19

Harvard University Initiative for Global Health

Obesity is an Independent Risk Obesity Levels, Trends and Burden Energy Balance Equation Theories of Obesity Trends Interventions and Policies

Harvard University Initiative for Global Health 1)For a long time, the independent health risks of obesity were controversial. A number of papers continue to argue that the effects of obesity attenuate with age and differ across race groups. 2)By excluding smokers and those with pre-existing medical conditions, the shape of the risk curve as a function of BMI shifts to a lower BMI. Key controversy is how many years of observation does it take to remove the full effect of pre-existing conditions. Risks of Obesity

Harvard University Initiative for Global Health

Obesity is an Independent Risk Obesity Levels, Trends and Burden Energy Balance Equation Theories of Obesity Trends Interventions and Policies

Harvard University Initiative for Global Health

Blood pressure, cholesterol and BMI vs. income Male Female

Harvard University Initiative for Global Health Trends in Measured Obesity

Harvard University Initiative for Global Health BRFSS Obesity Females, year moving average

Harvard University Initiative for Global Health Changing US income-BMI relationship

Harvard University Initiative for Global Health

Obesity is an Independent Risk Obesity Levels, Trends and Burden Energy Balance Equation Theories of Obesity Trends Interventions and Policies

Harvard University Initiative for Global Health Change in Weight = Net Energy Intake – Net Energy Expenditure Energy Balance Equation

Harvard University Initiative for Global Health Energy Intake Increased number of meals – snacking Increased size of portions Increased energy density of foods Food composition leading to changes in effective energy availability Energy Expenditure Decreased physical activity at school and work Decreased leisure time physical activity Explanations for Obesity Trends

Harvard University Initiative for Global Health In the absence of homeostatic mechanisms, a slight change in caloric intake, e.g. one soft drink a day, could account for the rise in average weight in the US. Subtle Shifts in the Energy Balance?

Harvard University Initiative for Global Health Obesity is an Independent Risk Obesity Levels, Trends and Burden Energy Balance Equation Theories of Obesity Trends Interventions and Policies

Harvard University Initiative for Global Health 1)Shift to ‘Western’ high-fat, low fibre diet due to higher incomes and globalization of the food industry – focus on fat composition of caloric intake 2)Urbanization and decrease of physical activity associated with shift from manual labour to industry and service sectors combined with technology revolution decreasing physical activity within any occupation. Nutrition Transition

Harvard University Initiative for Global Health 1)Main change in the energy balance is the rise of eating between meals which has been facilitated by food processing technologies (good tasting long lasting) and increased availability of snack foods sales points throughout society. 2)Some studies identify the main culprit at liquid carbohydrates (soft drinks and sweetened fruit juices) which have increased enormously in the last decades. Liquid carbohydrates may not trigger normal satiety mechanisms. Snacking Theories

Harvard University Initiative for Global Health 1)In previous times, food accounted for 80% or more of household income. Food consumption was associated with elaborate rituals. 2)Patterns of food consumption have been changing dramatically: rise of eating out of the home, eating prepared food in the home, increased portion size (especially in the US), fast food restaurants as a global phenomenon. Culture of Food

Harvard University Initiative for Global Health 1)Humans are the only higher primate that cooks their own food starting 1.6 million years ago. They likely ate one meal a day after hunting/gathering during the rest of the day. Humans also faced famines. Both probably led to a highly effective capacity to store excess energy as fat. 2)These thrifty genes in an environment of constant plenty lead to excess weight gain. Genes Environment Mismatch

Harvard University Initiative for Global Health

A major thrust of the public health message in the 70s and 80s was to adopt a low-fat diet. Food industry responded with many products marketed as low-fat. Many low-fat products are high carbohydrates and high energy intake. Did the promotion of low-fat foods without regard to total caloric content contribute to increased energy intake and obesity? Is Public Health Partly to Blame?

Harvard University Initiative for Global Health Some analysts see multinational business as the main driver of the obesity epidemic: US agricultural subsidies generate huge surpluses of sugar for which the sugar industry has tried to generate markets: soft-drinks, sugar additives to yoghurt, fruit juices etc. Fast-food industry has been trying to increase sales through supersizing, marketing food with toys to children, and global expansion. Processed food industries have been trying to increase total market through advertising and penetration of developing country markets. Global Food Industry

Harvard University Initiative for Global Health Because data on both diet and physical activity are so poor, the trends in energy intake and energy expenditure in the US are controversial. NHANES data support a rise in total caloric intake while the proportion from fat declined. Other sources claim that there has been no change in total energy intake, only a change in composition from fat to carbohydrates. There are no benchmarked measurements of physical activity overtime. US Energy Balance Trends

Harvard University Initiative for Global Health Obesity is an Independent Risk Obesity Levels, Trends and Burden Energy Balance Equation Theories of Obesity Trends Interventions and Policies

Harvard University Initiative for Global Health 1)Randomized trials of diets, behavioural counselling, promotion of physical activity, with and without pharmacological intervention suggest maximum sustainable weight loss is 10%. Over 5 year period, almost no one sustains weight loss. 2)Low-carb, high-fat diets in several studies show weight loss of 4-6 kilos in the short run. Atkins movement had a detectable impact on national diet but this effect seems to be waning. Consequences are not known. 3)Rising rates of surgery for stomach reduction which provide about 10% reductions in long-term weight. Promoting Weight Loss

Harvard University Initiative for Global Health Given dismal results to date of weight reduction interventions, an important component of current options is to aggressively deal with other cardiovascular risk factors that are often correlated with obesity: blood pressure and cholesterol. Minimizing Harm of Obesity

Harvard University Initiative for Global Health 1)Decrease availability of energy-dense snacks especially beverages to children in school. 2)Promote physical activity in schools, make the environment more conducive to physical activity, e.g. sidewalks. 3)Change national diet recommendations to reduce percent of free sugars; work with food industry to provide alternatives. 4)More aggressive state intervention to shift the national diet through taxes and regulatory mechanisms. Population Strategies

Harvard University Initiative for Global Health 1)Solutions to the obesity epidemic are unlikely to come from providing better information to the public through media campaigns, product labelling or counselling. 2)As for alcohol, the issue of how much we want the government to actively attempt to change national diet and exercise patterns will become central. Individual Choice vs. Population Health