Making Fat Work

Abstract

The burgeoning obesity and metabolic disease epidemics in the developed world are exerting a terrible toll on society, yet the precise mechanisms responsible for the emergence of these dramatic trends over a relatively short period of time remain poorly understood. Philip A. Wood’s book How Fat Works provides important insights into cellular lipid metabolism, as well as discussing some of the important external contributors to the development of human obesity. The foundation provided by this book allows for the exploration of how body fat has gone from hero during the millennia when starvation was the paramount nutritional risk to its current role as villain in our period of caloric excess. With the incredible personal and societal costs brought about by excess body weight, a comprehensive understanding of the mechanisms responsible for obesity is fundamentally necessary if we are to reverse these dire trends. Here, we delve deeper into some of the forces contributing to the obesity epidemic and discuss some individual measures as well as public policy decisions that may help reverse weight trends, while specifically focusing on the growing problem of pediatric obesity.

In his book How Fat Works, Philip A. Wood provides an invaluable assimilation of knowledge regarding how humans metabolize lipids with the goal of explaining the interplay of genetics, pharmaceuticals, and various lifestyle changes on the deposition and mobilization of body fat in humans. Written in a style that is accessible to individuals with some scientific background, the book efficiently builds a foundation of fat metabolism upon which he weaves a cogent discussion of controversies in the field of human nutrition, ranging from the debate about the appropriate macronutrient content of diets that may best facilitate weight loss to a discussion of how food labels leave us in the dark about what we are actually consuming. Spanning the gamut from the molecular metabolism of lipids to broader questions of public policy, this fine work serves as an excellent launching pad for discussing some of the myriad contributors to the fattening of the United States, and indeed the world.

Rapidly Expanding Waistlines: The State of the Crisis

Wood’s book is organized into four sections of chapters focused on tackling particular aspects of fat metabolism and some of the factors that contribute to body weight. In the first section entitled “Problems of Excess Fat and Cholesterol,” Wood introduces the crisis of obesity in his chapter “The Burden of Obesity.” Data that has emerged since publication of How Fat Works in 2006 reinforce the incredible extent of this epidemic, as well as some of the disturbing trends that have accompanied it. For example, data from the most recent National Health and Nutrition Examination Survey (NHANES) collected in 2007–2008 shows that the overall age-adjusted obesity rate (defined as a body mass index [BMI] ≥ 30 kg/m²) is now 33.8% among adults 20 years of age or older, while the prevalence of overweight (defined as a BMI ≥ 25 kg/m²) is a startling 68.0% (Flegal et al. 2010). This represents a dramatic shift over the last three decades. In the first National Health Examination Study in 1960–1962, the prevalence among adults age 20–74 of overweight and obesity were remarkably lower, 31.5% and 13.4% respectively (Flegal et al. 1998). Even more surprising has been the rise in extreme obesity (BMI ≥ 40 kg/m²), which represented only 0.9% of the population in 1960–1962 but ballooned to 5.7% in 2007–2008. The data trends suggest that the tendency toward greater fat accumulation began to dramatically accelerate in the 1980s for reasons that remain incompletely understood. Thus, over only a few short decades, a vast majority of the United States accumulated abnormal amounts of body fat, with the U.S. population as a whole gaining approximately 3 billion pounds in the 1990s alone (Ogden et al. 2004).

Embedded in the NHANES data is a disturbing trend in the distribution of overweight and obesity among specific ethnic and racial groups. The most recent NHANES data reveal prevalence rates of obesity that are greater among non- Hispanic blacks (44.1%) and Hispanics (38.7%) than among their non-Hispanic white counterparts, a trend that is also true for extreme obesity (Flegal et al. 2010). Furthermore, the rates of weight gain have been greater among minority groups than among the non-Hispanic white population. The rise in overweight and obesity has been accompanied by a simultaneous rise in the attendant metabolic consequences of obesity (insulin resistance, type 2 diabetes, hyperlipidemia, and hypertension) that disproportionately burdens minority groups (Cowie et al. 2010). In a perfect storm of negative forces, these groups are also the least likely to have access to quality health care to mitigate the impact of these diseases, or to the quality education that may facilitate better self-efficacy in addressing health problems. Furthermore, the rise in rates of overweight and obesity in the developing world may create an even greater challenge, as these countries may lack the necessary health infrastructure to offset the metabolic consequences of excessive weight gain. As such, the obesity epidemic and its health consequences represent an increasingly important source of health disparities that threaten the ability of minority groups and those in the developing world to escape poverty.

The urgency of the obesity epidemic has been heightened by the growing recognition that obesity is no longer the sole problem of adults and is plaguing children as well. The problem of pediatric obesity appears to have transformed the discussion of the origins of obesity because of the perception that obese children are more likely the victims of an obesogenic environment that is largely out of their control. The pervasiveness of this health crisis is sobering. Defining overweight as a BMI ≥ 85th percentile for age and obesity as a BMI ≥ 95th percentile for age (Krebs et al. 2007), the 2007–2008 NHANES data reveals that the obesity rates among children 2–5 years of age is 10.4%, 6–11 years of age is 19.6%, and 12–19 years of age is 18.1%; rates of overweight are 21.2%, 35.5%, and 34.2%, respectively (Ogden et al. 2010). These represent staggering increases when compared to data gathered by the NHANES study in 1976–1980, which revealed obesity rates of 5%, 6.5%, and 5% for children 2–5, 6–11, and 12–19, respectively. As is the case with the data for adults, non-whites bear a disproportional burden of overweight and obesity. Further troubling is the not-unexpected appearance of heretofore “adult” diseases like type 2 diabetes and cardiovascular disease in overweight and obese teenagers (Berenson et al. 1998; Sinha et al. 2002). This earlier onset of metabolic diseases is now predicted to result in the first cohort of children to see a reduction in life expectancy relative to their parents’ generation (Olshansky et al. 2005). The potential of this crisis to wreak havoc on future generations has caught the nation’s attention. First Lady Michelle Obama (2010) has made tackling childhood obesity a major focus of her work, and President Obama (2010) has supported this effort through an Executive Order establishing a Task Force on Childhood Obesity. Because of the burden placed on children and minorities, obesity is becoming one of the central social justice issues of our day. The challenge will be to use this momentum to develop a comprehensive understanding of the underlying causes responsible for the surge in obesity and to devise strategies to reverse these disturbing trends.

Compounding Problems: Failing to Match Energy Intake with Energy Expenditure

In his chapter entitled “The Energy Equation,” Wood lays out the very basic fact that weight gain is a consequence of the first law of thermodynamics, specifically that energy stored as fat is a result of energy intake (in the form of food calories) being in excess of energy expenditure (that needed to maintain cellular processes and perform mechanical work). As such, humans are set up to very efficiently accumulate fat whenever energy input is increased (e.g., larger meal sizes or higher meal frequency) or energy output is decreased (e.g., less voluntary exercise or transition to more sedentary activity). Over the last three decades, we have seen transformations in our society that have led to an increase in caloric consumption. From 1971 to 2000, caloric consumption among women has increased 22% (from 1,542 calories/day to 1,877 calories/day) while men have increased consumption 7% (from 2,450 calories/day to 2,618 calories/day) (MMWR 2004). Trends in physical activity suggest that there have been some increases in leisure-time physical activity; however, work-, home-, and transportation- related activity have declined, while sedentary activity has increased (Brownson, Boehmer, and Luke 2005). As a result, most individuals still fail to meet recommended levels of activity, with women, ethnic and racial minorities, and the less-educated the least likely to meet activity targets (TRB 2005). These trends in energy-in and energy-out synergize to promote obesity. Interestingly, they also represent a fundamental shift in our relationship with our environment as we have transitioned from hunter-gatherers to passive consumers of the Western lifestyle. The deleterious impacts of this change, as well as the benefits of returning to a more ancient way of life on metabolism, have been described in Australian aborigines (O’Dea 1991) and may provide important insights into the way forward.

The elegant thermodynamics of fat storage provide insights into the insidious nature of obesity. Other things being equal, consuming a mere 10 excess calories per day would be predicted to result in approximately one excess pound of body fat per year, or 10 pounds per decade. Therefore, the transition from schooling to middle age can be marked by the addition of 30 pounds of excess weight. And 10 calories is not a significant amount of excess calories: it is equivalent to three grapes, 2/3 teaspoon of sugar, or a mere 1.9 grams of potato chips. Given how such a small change can accumulate over long periods of time, it is not surprising that we are enlarging as a society. As such, a strategy of matching energy expenditure with energy intake is critical for weight maintenance. Alternatively, given a set rate of energy expenditure, meals that provide calories in excess must be compensated for by a reduction in calories at other meals. Balancing out calorie consumption can be quite difficult, however, since food intake may not be matched to hunger signals but instead be driven by other energy-unrelated forces, such as easy availability or advertising. Evidence suggests that young children are able to modulate food consumption for previous caloric intake; however, this regulation appears to be lost as people age and non-nutrition signals take hold (Birch and Deysher 1986; Kral et al. 2007). Consequently, conscious efforts to monitor and adjust caloric intake are critical for long-term weight maintenance.

The importance of weight maintenance is underscored by the fact that sustained weight loss after weight gain is an exceptionally difficult endeavor for many people. This may, in fact, be an adaptation resulting from evolutionary pressure to preserve energy stores (i.e., body fat) during periods of food scarcity in order to improve chances of survival. Recent data has demonstrated a physiological shift in energy utilization that antagonizes weight loss. Research subjects forced to lose as little as 10% of their body weight (and perhaps less) demonstrate a reduction in energy expenditure in an effort to restore fat mass (Goldsmith et al. 2010). This data is consistent with the concept of a body fat set-point that the individual’s homeostatic mechanisms attempt to defend against changes in body weight. While this feedback to limit weight loss may have been advantageous to our ancestors during periods of starvation, the consequence in our current times of plenty is likely the extreme difficulty individuals have in sustaining weight loss. Further complicating matters, our bodies appear to protect that set-point unidirectionally, so that weight loss is fought against while weight gain seems virtually unrestricted. This paradox allows for the establishment of new, ever higher set-points that the body will then aggressively defend, even if it is advantageous for the health of the individual to lose the excess weight (Schwartz et al. 2003).

The hypothalamus plays a critical role in the establishment and maintenance of energy balance and body weight (Leibel 2008). This region is at the base of the brain and thus occupies the interface between the central nervous system and peripheral tissues. In order to ascertain an individual’s energy stores and energy demand, the hypothalamus summates a wide variety of disparate inputs, including higher-order brain signals, metabolites and hormones in the plasma, and specific factors such as leptin that are secreted from adipocytes in proportion to energy flux into these cells. The precise mechanisms by which the hypothalamus establishes an ideal weight set-point and then exerts its influence to defend it are not fully understood, but it is clear that adipose tissue plays a central role in both sides of this process. Since the lifespan of an adipocyte is approximately 10 years (Spalding et al. 2008), overcoming the body’s desired fat content in order to lose weight would require a significant turnover in that adipocyte pool, thus necessitating sustained effort to maintain weight loss over at least a decade before a reasonable change in set-point signaling could be expected to occur. Furthermore, during weight gain adipocytes undergo both hypertrophy (increase in cell size) as well as hyperplasia (increase in cell number), yet during weight loss it is not clear that the fat cell number is reduced as opposed to solely a decrease in individual fat cell size. Thus, coupled with the long adipocyte half-life, mounting evidence suggests that alterations in the adipocyte-hypothalamus signaling axis that can occur relatively rapidly during weight gain may require years or even decades to overcome in order to reestablish the ideal body weight setpoint. This would undoubtedly require considerable personal effort to achieve and may help explain the fact that most people who lose weight gain much of it back over time.

But a careful assessment of weight gain must also take into account the other side of the energy equation, namely energy expenditure, which is also diminished in many overweight and obese individuals. In the clinic, patients will frequently report that they don’t have the time to exercise; however, many also tell us that they lack access to outdoor activities because of safety concerns in their community. Regardless of the reason for poor exercise habits, addressing energy “output” is fundamentally important to helping reverse the obesity epidemic. In Chapter 14, “Exercise to Burn Fat,” Wood discusses the ways in which exercise beneficially impacts energy metabolism. It is becoming increasingly clear that exercise is particularly important for sustaining weight loss once it is achieved (Anderson et al. 2001; Weiss et al. 2007). In addition to contributing to weight loss through caloric expenditure, exercise improves overall metabolic health by improving insulin sensitivity (Perseghin et al. 1996). The prescribed exercise regimen that may best facilitate weight loss is not fully characterized, but it likely will include resistance training. Resistance exercises appear to increase resting energy expenditure (Fatouros et al. 2009), which may overcome the adaptive compensatory decrease observed with weight loss. Given the failure of such a large portion of the population to meet physical activity recommendations, however, any increase in physical activity will likely have beneficial effects on the health of the population.

Friend or Foe? The Food Industry and Consumption

To understand the dynamics of the obesity epidemic, it is important to appreciate the toll of overweight and obesity on society within the context of related social forces. Obesity-related health care costs in the United States are estimated to be as high as $147 billion annually (Finkelstein et al. 2009). With the Centers for Medicare and Medicaid Services projecting health-care costs to grow to 19.3% of GDP by 2019, and obese individuals requiring higher lifetime health spending (Lakdawalla, Goldman, and Shang 2005; Yang and Hall 2008), this number undoubtedly will spiral upwards in the coming years. This burden on the economy necessitates a concerted effort to reverse the burden of obesity; however, understanding the magnitude of that task requires an appreciation of the fact that, for some sectors of our economy, obesity is actually an economic stimulus. Increased food consumption supports the many companies in the food industry, their employees, and their shareholders. The central role of the food industry in the American economy is underscored by data from the Bureau of Labor Statistics Consumer Expenditure Survey, which shows that food purchases constituted nearly 13% of average annual expenditures, or nearly $780 billion across the economy in 2008 (BLS 2010). The share of the food dollar spent on items prepared outside of the home has increased from 18% to 32% from 1977– 1978 to 1994–1996 (Guthrie, Lin, and Frazao 2002). The National Restaurant Association projects that the restaurant industry share will rise to 49% with restaurant sales projected to be on the order of $580 billion in 2010 (NRA 2010). The power of the food industry is further enhanced through their lobbying efforts, which totaled nearly $1.2 billion between 1998 and 2009 (CRP 2010). This substantial investment in government influence is understandable when considering that agricultural subsidies in the United States amounted to $177.6 billion from 1995 to 2006 (EWG 2010).

The influence of food manufacturers is extended directly to consumers to augment our food consumption through ingenious fast-food marketing campaigns. Such advertising efforts have assumed greater significance with the increasing number of meals consumed outside of the home. The impact of those meals is further enhanced by data that suggests that portion sizes at restaurants are larger than those made at home, and larger portion sizes are implicated as a cause of our increased caloric consumption (Briefel and Johnson 2004). One of the great recent examples of a clear nutrition distortion is Taco Bell’s “Fourth Meal” campaign. The advertising blitz associated with this campaign advocates the consumption of a post-dinner, pre-breakfast meal. The encouragement to add a meal to an already excess amount of dietary calories can only exacerbate obesity rates. This is not to say that Taco Bell is not making some efforts to mitigate the impact of fast food on health. Their “Fresco” menu offers lower calorie options that are a great alternative to their traditional fare. However, the “Fourth Meal” campaign counteracts any efforts by Taco Bell to offer healthier alternatives. And Taco Bell is certainly not alone in their distortion of meals: other fast-food restaurants are no less guilty of manipulating our perception of their products. During the Vancouver Winter Olympics, McDonald’s advertised their foods using athletes from the games as their spokespersons. The implicit message in this is that thin, athletic Olympic athletes eat at McDonald’s, so you can too. But what is lost is the message that the athlete’s consumption of such high calorie food is offset by the expenditure of thousands of calories per day in exercise, levels that are matched by few ordinary McDonald’s customers.

One of the food industry practices that rankles researchers in the field of nutrition the most is their direct-to-children advertising, which amounted to $1.6 billion in the United States in 2006 (Kovacic 2008). According to the Federal Trade Commission, the average U.S. child (aged 2–11 years) is annually exposed to approximately 5,500 food advertisements on television amounting to 2200 minutes, 98% of which were for foods of poor nutritional value (Holt 2007; Powell et al. 2007). The effects of this advertising on food consumption has been a source of contention between public-health advocates and the food industry regarding whether food advertisements per se influence obesity rates, or whether the effects of television on weight gain are simply a consequence of associated snacking or because viewing is a sedentary activity. A report from the Institute of Medicine (2006) assessing the effect of food marketing to children aged 2–11 years found strong evidence to suggest that television advertising influences food preferences and is associated with body fat. While the food industry may continue to contest this connection, it would be poor business to invest billions of dollars so heavily in advertising to children and adolescents if it didn’t have an effect on food intake. Since caloric consumption has increased over the last few decades and this has undoubtedly contributed to weight gain, it is not an intellectual leap to suggest that advertising has contributed to this phenomenon.

Collectively, this data suggests that the food industry has a tremendous influence on the foods we consume as well as on the country’s overall food policy. Thus, a fundamental conflict is established between the immediate economic interests of the food industry and the deferred health-care costs of obesity. Furthermore, the costs of an obese society are not directly borne by those that benefit from obesity: the food industry cashes the check while the government pays the bill. Moreover, lobbying efforts by agribusiness undoubtedly create a conflict for lawmakers who must make the tough policy decisions necessary to reverse the spread of obesity, many of which are likely to be against the interests of the food industry. However, because of their considerable contribution to the economy as well as the importance of a maintaining a robust food supply, food manufacturers must become an important partner in the diet solution. An example of how this might work occurred in 2004, when General Mills converted all of their cereals to whole grains. While many of these cereals are still loaded with sugar, this was an important step forward. The challenge will be for food manufacturers to make more meaningful changes that may put their core businesses at risk (e.g., sugar-sweetened beverages). But without their aggressive commitment, efforts to achieve meaningful changes in our metabolic health will likely fail.

Individual Action: Improving Personal Health Choices

While obesity is a global problem, its immediate solution rests in the hands of individuals. Since weight gain for the vast majority of people is a consequence of energy intake exceeding energy expenditure, the basic advice for weight loss is to attempt to cut down on caloric intake while increasing physical activity. Given the significant amount of activity required to burn excess calories, the easiest means to generate negative energy balance is to consume fewer calories. However, the hypocaloric diet most likely to facilitate weight loss is still somewhat controversial. In his chapter “Breaking the Insulin Cycle,” Wood argues in favor of a diet whose macronutrient composition is relatively high fat–low carbohydrate, in contrast to the more traditional approach of a hypocaloric diet that is relatively high carbohydrate–low fat. The premise upon which this advice is based is the fact that secretion of insulin, the primary anabolic hormone active in the body, is primarily driven by blood glucose derived from dietary carbohydrates. Since insulin drives fat deposition, efforts directed at decreasing levels of this hormone may be particularly effective at dropping weight. This notion is further supported by the fact that the deposition of the metabolically deleterious visceral fat above the waist (the classical “apple” phenotype) is dependent on high insulin levels. Reductions in insulin levels may allow this depot to mobilize its fat stores. While the increase in free fatty acid released from visceral fat stores may transiently increase insulin resistance (Bergman and Ader 2000), long-term depletion of the visceral fat compartment would be expected to reduce insulin resistance and thereby further lower insulin levels, thus improving the overall metabolic picture of the patient. In addition to decreasing fat deposition, reductions in insulin levels would be expected to increase HDL (“good”) cholesterol while lowering triglyceride levels, an overall improvement in the cardiovascular risk profile (Willett and Leibel 2002).

Historically, efforts directed at weight loss have focused on reducing the fat content of food. The central premise seemed to revolve around the false notion that fat in the diet was responsible for the totality of fat deposited in the body. That message seems to have been encouraged by food marketers who tout their products’ “fat-free” status as an important selling point. But there is a tremendous difference between being free of fat and not promoting the deposition of fat in vivo. One of the strengths of How Fat Works is Woods’s delineation of the biochemistry of fatty acid synthesis in the chapter entitled “Making and Storing Fat.” From this discussion, it is clear that calories consumed as carbohydrates are efficiently turned into fats in vivo. Further, those fats synthesized from carbohydrates are generally of the saturated variety, the type of fats that have the worst effects on health. This is an important message, since the public’s consumption of carbohydrates as a percent of total calories has increased over the last several decades in concordance with obesity rates (Willett and Leibel 2002).

The understanding of carbohydrate-generated fat and the role of insulin in promoting fat deposition spawned the low-carbohydrate diets promoted by Robert Atkins and others. The central concern with these diets was their impact on lipids and cardiovascular disease; however, high carbohydrate diets are known to increase triglycerides and decrease HDL, two changes in the lipid profile that are by themselves predicted to increase cardiovascular disease risk. A further question has been whether high-fat, low-carbohydrate diets can lead to durable weight loss. Since the publication of How Fat Works, longer-term studies have shown that, at the least, diets low in carbohydrates do not significantly increase cardiovascular risk and may be more effective in achieving rapid short-term weight loss relative to a low-fat diet (Gardner et al. 2007). The basic biochemistry of fat synthesis from macronutrients, the known anabolic effects of insulin, and the data regarding the likely safety of low-carbohydrate diets argue in favor of such a diet as a means of facilitating individual weight loss; however, longer-term studies are still needed to vigorously defend such an approach.

Despite that caveat, it is absolutely clear that some excessive carbohydrates should be aggressively removed from our diet immediately. Unlike fruits, vegetables, and dietary fiber that provide carbohydrates alongside other important nutrients and that may actually decrease an individual’s risk of developing obesity (Yao and Roberts 2001), much of the increase in carbohydrate (and calorie) consumption in recent decades comes from an increase in high-calorie, carbohydrate- based foods with little nutritional value, namely snack foods (chips, cookies, candy) and sugar-sweetened beverages (soda, juices with added sugar). From 1977–1978 to 1999–2001, total calories consumed rose from 1,790 to 2,068 calories/day (Nielsen and Popkin 2004). Even more alarming, the percent of total daily calories consumed as sweetened beverages increased from 3.9% to 9.2%, or in absolute caloric terms, sugary drinks contribution to total calories in the diet rose from 70 to 190 calories/day (remember that just 100 excess calories/ day can result in 10 pounds of weight gain per year). Over this period, those aged 19–39 years had the greatest increase (5.1% to 12.3% on a total calories increase from 1,855 to 2,321 calories/day); however, children aged 2–18 years also experienced a dramatic increase in sweetened beverage consumption from 4.8% to 10.3% of total daily calories, while their total daily calorie consumption increased only modestly from 1,839 to 1,917 calories/day. Thus, it appears that an increasing percentage of children’s caloric consumption comes from foods and beverages that offer little nutritional value. Moreover, these calories have replaced more nutritious foods. The increasing portion of the diet coming from sugar-sweetened beverages appears to be the result of both an increase in the number of servings per day as well as an increase in the size of those servings. While pursuing an overall carbohydrate-restricted diet may be up for debate, the elimination of calorie-containing beverages, particularly those that are sugar-sweetened, would be an important first step in individual weight loss.

Given the challenges to weight loss, both in terms of modifying long-standing behaviors as well as fighting the body’s own resistance to weight changes, it becomes imperative to focus attention on preventing obesity. In essence, an ounce of prevention is worth many kg/m2. With the population of obese children growing rapidly, much of this effort should be directed at preventing pediatric obesity and developing sound health habits early in life. Recent clinical guidelines issued jointly by the Endocrine Society and the Lawson Wilkins Pediatric Endocrine Society provide a framework for some of the individual interventions that will be necessary to reverse the astounding trends in obesity and its attendant metabolic consequences in the pediatric population (August et al. 2008). These guidelines focus on lifestyle changes, including modifications to eating habits that consist of avoidance of calorie-dense, nutrient-poor foods; portion control; reduction in saturated fat intake coupled with an increase in dietary fiber, fruits, and vegetables; and eating regular meals (including breakfast) while avoiding “grazing” patterns of consumption. In addition to the food intake recommendations, the combined societies recommend 60 minutes of moderate to vigorous physical activity daily, as well as a reduction in “screen time recreation” (television, video games, computer use) to one to two hours per day, as has been advocated by the American Academy of Pediatrics. While studies of weight-loss drugs and surgery have begun in adolescents, these therapeutic options are appropriately restricted to particular circumstances (extreme obesity with associated co-morbidities), given the potential for adverse events.

It Takes a Village: Societal Change for a Healthier Population

The ability of adults and children to make these lifestyle modifications to improve health will certainly be difficult, but it will be nearly impossible without meaningful changes in public policy that influence how our food system interacts with us. While some individuals will be able to lose significant weight and sustain that weight loss over time, it is unrealistic to expect the nearly 70% of Americans who are overweight to swim against the current of consumption and normalize their body weight and metabolism without significant changes to how food is produced, sold, and consumed around the world. This is underscored by interesting data from the Framingham cohort suggesting that social networks may be a contributing factor to the emergence of obesity (Christakis and Fowler 2007). In this study, having a friend or relative who was obese increased the likelihood that an individual would also become obese. Thus, it becomes imperative for everyone to work together to improve health across the population. This includes individuals organizing together to demand better options; the food industry making earnest efforts to improve the nutritional value of the food they supply; and politicians willing to modify public policy to place public health ahead of special interests. Through such collective action it may be possible to create a competing social force centered around a culture of health based on improved nutrition and daily exercise in order to reverse the deleterious trends in weight gain observed over the last several decades.

The first step in achieving meaningful cultural change is to identify the systemic problems that contribute to maladaptive food consumption. The increasing intrusion of sweetened beverages into our diet reflects an overall trend of heavier reliance on processed “convenience” foods that likely reflects increasing demands on our time. In some neighborhoods, however, the consumption of processed foods is a result of skewed market availability. Low-income neighborhoods often become food deserts, in which access to fresh fruits and vegetables is extremely limited while the relative proportion of high-calorie foods of limited nutritional value is increased (Larson, Story, and Nelson 2009). Making smart lifestyle choices becomes exceedingly difficult when access to healthy options is limited. It is no wonder then that minority groups are experiencing overweight and obesity rates that are greater than the national average. To help reverse this important nutritional disparity, efforts should be made to increase the availability of fresh fruits and vegetables in low-income neighborhoods.

Facilitating increased caloric consumption is the fact that, correcting for inflation, food prices actually dropped between 1980 and 2000 (Finkelstein, Ruhm, and Kosa 2005), after having increased from 1960 to 1980, in the period prior to the obesity epidemic. The problem emanating from this data is the finding that the cost of less-healthy foods has decreased relative to the costs of healthier alternatives. Finkelstein and colleagues report that “Between 1985 and 2000, the price of fresh fruits and vegetables, fish, and dairy increased by 118%, 77%, and 56%, respectively, whereas sugar and sweets, fats and oils, and carbonated beverages increased at lower rates—46%, 35%, and 20%, respectively” (pp. 244–45). If “value” is conceived of as calories per dollar, the period post-1980 has seen an increase in the desirability of low-nutrition foods, while society at large has seen an increase in obesity rates and the attendant health-care costs associated with it.

The price distortion of cheaper but nutritionally deficient foods can be addressed through public policy. In an effort to address this cost-benefit mismatch, some have advocated a “soda tax” or a “junk food tax,” through which sweetened beverages and snacks of poor nutritional value would be taxed both to discourage their consumption as well as to generate revenue to defray the healthcare costs associated with obesity. The rationale for such a tax is supported by evidence that at least some of the excess caloric consumption that leads to obesity is derived from snacks and sweetened beverages (Nielsen and Popkin 2004). This could be an important means of improving nutrition because it may act as a powerful disincentive to consume those foods that are thought to be the source of much of the excess calories responsible for our increasing rates of obesity. Further, if the money generated from such a tax were directed toward offsetting the costs of health care, it could help close the loop on the economic toll exerted by obesity. A recently published study examined the effects of taxes and subsidies on food purchases in an experimental model (Epstein 2010). The researchers found that subsidies on healthy foods did not improve the macronutrient profile nor the energy content of the foods purchased; however, taxes on less healthy foods resulted in a decrease in overall caloric intake while simultaneously reducing the amount of fat purchased. While this experiment showed the potential utility of such a junk food tax, the real-world implications are more difficult to infer from a controlled laboratory setting. In another experiment, however, researchers followed participants in the Coronary Artery Risk Development in Young Adults (CARDIA) study over a 20-year period (Duffey et al. 2010). The investigators found that increasing the price of soda or pizza by 10% reduced energy consumption from these foods by 7.1% and 11.5%, respectively. Further, increasing the price of soda by $1 was correlated with a reduction in daily energy intake, improved body weight, and greater insulin sensitivity. The decrease in energy intake and improvement in insulin sensitivity were greater when the price increases for multiple foods were combined.

These controlled and natural experiments suggest that modifying the price of foods with poor nutritional value can lead to significant changes in food consumption. Given the contribution of sugar-sweetened beverages and other unhealthful foods to the increase in caloric intake that underlies the obesity epidemic, using economic tools to guide consumer behavior would make a great deal of sense. It is clear, however, that efforts to promote such taxes will confront resistance from both the food industry and those who oppose taxes. Yet with experimental evidence supporting such an approach, it will be worthwhile to face these challenges, because such an approach may be particularly helpful in limiting children’s consumption of foods devoid of nutritional value. Since children have limited purchasing power, they would be more likely to modify their behavior if such a tax were sufficiently robust. In the absence of such a pricing strategy, efforts to remove convenience foods and sugar-sweetened beverages from schools would be another approach, as lack of access will undoubtedly curb children’s consumption of nutritionally poor foods. Unfortunately, vending machines serve as an alternative funding mechanism for many cash-strapped school systems, which may make elimination of such items difficult to swallow; on the other hand, evidence suggests that replacing nutritionally poor foods with healthier alternatives may be revenue-neutral.

Eating food outside the home also distorts caloric consumption because the nutritional content of restaurant food is often a mystery. In the chapter entitled “Nutrient Labeling,” Wood argues for the clear and unambiguous labeling of nutrition information that is available and obvious to the consumer prior to the food’s purchase. This is particularly important in restaurants, since serving size is open to a great deal of interpretation. As an example, take a single hamburger. Most people would likely conceive of one hamburger as a uniform serving size; however, depending on where you eat, the caloric content of that burger could vary by a factor of 10. For example, aWhite Castle burger, albeit small in size, is only 140 calories while a Red Robin A.1. Peppercorn Burger is 1433 calories. The hope would be for patrons to be supplied with this information on the menu so they may choose to mitigate the unnecessary caloric excess at Red Robin through either meal sharing, eliminating caloric beverages, or forgoing the accompanying French fries. Some intervention trials suggest that providing nutrition information may modulate behavior in a favorable way (Roberto et al. 2010). Data also suggest that parents provided with nutrition information will choose meals for their children with fewer calories (Tandon et al. 2010). At the bare minimum, public policy should advocate nutrition labeling, as this doesn’t place restrictive prohibitions on any food from being sold, but it empowers the consumer to make smart choices. As it stands now, precisely what we’re consuming is often unknown, and we cannot expect people to make smart decisions if we do not provide them with the necessary tools to do so.

For food labeling to have a meaningful impact on consumer behavior, there will need to be a strong commitment to nutrition education. Current education policy that emphasizes test scores above all else (e.g., No Child Left Behind), as well as decreasing school funding, challenge such an addition to the curriculum; however, it is vitally important for schools to become fully engaged in the fight against obesity. This must also include a reinvestment in physical education. In an ironic twist, the disappearance of gym classes and recess from the school day in favor of more classroom time not only may have contributed to the obesity epidemic but also may have impaired school performance, since physical activity has salutary effects on learning (Keays and Allison 1995). This loss of school-based exercise has been exacerbated by a disappearance of the “built-in exercise” that used to come from walking, bicycling, or taking the stairs. With more children taking the bus to school or getting rides, in-school activities become more important for improving fitness. Failing to do so will leave all of our children metabolically behind.

While these are just some of the means by which efforts on the community level can facilitate healthier lifestyle habits, further suggestions are put forth by a 2009 report from the Institute of Medicine entitled Local Government Actions to Prevent Childhood Obesity. Many of the IOM’s proposals are consistent with those promoted by the Endocrine Societies; however, additional recommendations for community action are also described. These include increasing access to healthy foods in communities (essentially irrigating food deserts with healthier food options); improving the availability and identification of healthful foods in restaurants; promoting overall access to fruits and vegetables; improving the quality of food offered by government programs; increasing participation in nutrition assistance programs; encouraging breast feeding (which is associated with a reduced risk of obesity in adulthood; Harder et al. 2005); implementing media and social marketing campaigns to advocate healthy nutrition, obesity prevention, and physical activity; increasing access to free, safe drinking water; and encouraging walking and biking for transportation, as well as programs to modify the physical environment to make walking and biking more safe. Implicit in the IOM’s recommendations are a special emphasis on addressing issues of health disparities that contribute to the poor and ethnic and racial minorities bearing a disproportionate burden of the obesity epidemic. Finally, as part of an overall goal to “reduce access to and consumption of calorie-dense, nutrient-poor foods,” the IOM recommends the implementation of a tax strategy to dissuade consumption of foods such as sugar-sweetened beverages that have minimal nutritional value. As discussed, this last proposal may represent the most difficult act of public policy to enact; however, it may also be one of the most powerful tools at our disposal. As we have seen with tobacco, economic policies can significantly change behavioral patterns, and behavioral change is precisely what we need to see in order to reverse the burden of the obesity epidemic that results in significant morbidity and mortality on the individual level while costing us billions of dollars on the societal level.

Conclusion

How Fat Works lays the foundation for examining the basis for altered energy homeostasis that has led to the obesity epidemic. Spanning the gamut from basic lipid biochemistry to the physiology of diet and exercise all the way to questions of public policy, Wood introduces many of the topics in human nutrition that are vital prerequisites for understanding the phenomenon of massive weight gain that has plagued society over the last three decades. With this background, we can begin to appreciate the constellation of interconnected factors that have conspired to increase body fat at both the individual and societal levels and that make weight loss on this same scale the great nutrition challenge of the present era. Through this understanding, however, we can begin to grasp the importance of a comprehensive approach to nutrition policy that actively engages all stakeholders. Significantly changing our metabolic health will require individuals, empowered with knowledge, to make smarter food choices while increasing their physical activity. These changes, however, can only happen with a strong commitment by the food industry to provide all citizens with access to healthy choices while simultaneously eliminating the current assault of nutritionally poor foods that are rich in sugar, fat, and salt. Creating such an environment will necessitate the development of sound public policy that favors sound nutrition and exercise through an appropriate price structure that discourages the consumption of junk food and encourages the consumption of fruits and vegetables, as well as through an aggressive campaign to promote physical activity. To this end, a major focus must be on the pediatric population. As has been discussed, preventing obesity will be much easier than trying to address excess weight after it has become ensconced. The current obesity crisis resulted from complex factors that evolved over decades. Reversing this epidemic and the tremendous toll it takes on society will require a society-wide commitment that must begin now.