What do we know about obesity and its prevention in the U.S.?

By Rebecca Haffajee

As many are aware, the New York City Board of Health recently approved Major Michael Bloomberg’s proposed ban on sugar-sweetened beverages (SSBs) over 16 ounces in size sold at city restaurants, delis, sports venues, movie theaters, and street carts. This “soda ban” is set to go into effect on March 12, 2013. It has been justified on the grounds that it will make headway in combating obesity in NYC.  It piggybacks on a number of other anti-obesity policies enacted in the City, including a transfat ban in restaurants, a requirement that chain restaurants post calorie information, initiatives to help low income residents buy fresh produce, and nutritional standards in schools. In this Blog, Katie Booth conducted a thorough legal analysis of whether the ban could be overturned, concluding that a plaintiff’s chances of waging a successful lawsuit are slim.  Meanwhile, robust commentary in the media and health journals has debated the legitimacy of the ban and government’s role in regulating SSBs and combating obesity.

So what do we know about obesity in the U.S. as a phenomenon, its causes, and possible interventions that work to combat its spread? Although the problem is far from simple, it’s useful to briefly compile the current evidence.

We know that obesity rates in the U.S. have exploded in the past several decades – just check out the shocking Centers for Disease Control animated maps showing the increases in prevalence from 1985-2010.  In 2009-2010, more than a third of American adults were obese (35.7% had BMIs ≥ 30); an additional third were overweight (BMI of 25-29.99).  A recent study found that obesity alone could exceed 60% in 13 states by 2030 if we continue on our current trajectories. Obesity, in short, is now a public health epidemic.

We also know that being obese/overweight is bad for your health. It increases the risk of type 2 diabetes, hypertension, and “bad” cholesterol, among other health conditions, and is associated with increased mortality in adults.  Obesity disproportionately affects non-whites and Hispanics and operates along the socio-economic income gradient (i.e., high income groups are less likely to be obese than low income ones).

The causes of obesity are a little trickier to pin down, though nutrition and lifestyle transitions are emerging as winning candidates. Essentially, we are consuming more calories than we expend, and gaining weight as a result. Many attribute this caloric imbalance to changes in the “food environment”, whereby food has become more available, convenient, calorie-dense, and abundant in portion sizes.  My favorite causal analysis by David Cutler, et al., essentially reasons by process of elimination to identify the decreased time cost of food preparation as the central obesity culprit.  So it’s not that our genes, energy output, wealth, information about food choices, or the affordability of food have changed significantly in the past few decades.  Rather, we are getting less healthy, more plentiful food fast and conveniently at restaurants, vending machines, cafeterias, and perhaps supermarkets (though the evidence of “food deserts” is mixed). SSB consumption, in particular, has been shown to be associated with higher rates of type 2 diabetes, weight gain, and obesity.   More research is still needed, though, to further unpack the biological and environmental risk factors underlying obesity.

Trickier still is identifying what interventions work to combat the obesity epidemic. The one intervention that does show promise is a “fat tax”.  A recent study in the British Medical Journal examined the most current studies on fat taxes (several of which used favorable methods such as randomized control trials). It found that taxes were effective in reducing consumption of unhealthy foods if the taxes met three criteria: (1) they must be at least 20% taxes; (2) they must apply to a wide range of unhealthy foods; and (3) the government must simultaneously with the tax offer healthy foods at subsidized rates. Nonetheless, taxes are critiqued on the basis that they are regressive — much like policies that restrict the use of food stamps for purchase of unhealthy foods — because lower income people spend a greater proportion of their income on food as compared to the wealthy.  But unfortunately, we don’t have a lot of evidence of other policies that work.  Also, taxes can be made more equitable if the revenues are invested in obesity prevention efforts for low income groups.

So why didn’t Mayor Bloomberg just pursue a tax instead of his panoply of interventions, including the recent “soda ban”? The answer is most likely political.  Gov. David Paterson tried to implement a penny-an-ounce tax on SSBs in the 2009 budget proposal for New York State. But anti-tax groups and the American Beverage Association spent millions to oppose the tax, and the measure was defeated. So even though the evidence suggests that taxes curb consumption of unhealthy foods, politics can get in the way, thereby requiring the pursuit of other interventions.  Virtually all obesity interventions that involve governmental regulation can be objected to on the basis that they infringe upon personal liberty and absolve individuals of personal responsibility.  Some believe that education and healthy “nudges” (with the voluntary help of unhealthy food manufacturers) are preferred and will be effective. Certainly these measures have been and should continue to be tried.  But the magnitude of the obesity epidemic suggests that we can’t waste any more time.  Major Bloomberg should be credited with trying innovative approaches in NYC, provided that robust, well-designed evaluations of all these obesity initiatives are put in place before implementation.  That is the only way we can truly learn from these pilots and develop multi-faceted, effective approaches to combating obesity.



Rebecca Haffajee is a Thomas O. Pyle Fellow in Pharmaceutical Policy Research in the Department of Population Medicine at the Harvard Pilgrim Healthcare Institute. After completing her JD and MPH at Harvard in 2006, Rebecca practiced as a health care lawyer for several years. She entered the Harvard PhD Program in Health Policy in 2010 with a concentration in Evaluative Science and Statistics. Her dissertation research is focused on the empirical effects of laws and policies on health outcomes, with particular emphases on public health laws and patient safety/quality initiatives. She is currently working on a longitudinal assessment of the impact of mental health parity laws on mental health treatment and outcomes. Rebecca was a Student Fellow at the Petrie-Flom Center in 2010 - 2011. Her research paper was: "Probing the Constitutional Basis for Distracted Driving Laws: Do they Actually Reduce Fatalities?"

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