Melissa Musiker is a registered dietician and a member of APCO’s Washington, D.C., health policy team.
Last week the American Society for Nutrition released a consensus statement on energy balance and implications for body weight regulation. In general, the statement supports much of the currently held notions about the importance of maintaining appropriate energy balance over time. It helps to clarify that there is no magic bullet; changes to intake and activity levels must be permanent to lose and maintain weight. Incremental, steady weight gain (which is what most people experience) occurs over time as energy expenditure slowly decreases and energy intake remains the same or creeps up.
Buried in the consensus report is a very important piece of information that has the potential to unravel just about every recent report on the economic impact of obesity and obesity prevention. The panel found that the “3,500 calories per pound” rule of thumb (the idea that for every 3,500 calories consumed or expended, a pound of weight is gained or lost) is frequently misapplied and is fundamentally flawed because no time frame is specified. Further it incorrectly gives the impression that temporary and relatively limited interventions will lead to permanent weight changes and gives an improper impression that there is a linear relationship between calorie intake/expenditure and weight over time. What the panel concluded was something that anyone who has ever been on a diet could tell you: weight management it is just so much more complicated than that. If it were really that easy, we’d all be a little bit thinner.
If this seems to you like the typical squabble over minutiae from ivory-tower academics, think again. The 3,500-calorie rule of thumb is a key assumption in most studies about weight management and chronic disease prevention policy, rendering many of findings of influential studies potentially invalid, as it leads to unrealistic predictions of the impact of marginal changes to diet or physical activity on weight, co-morbidities of obesity and ultimately health care costs and economic impact.
If you are someone who likes numbers and calculations, the panel recommends an alternative estimation method that every permanent 10-calorie-per-day change in energy intake will lead to about a half-pound of weight change over the course of a year, and about one pound over three years. In essence, increasing physical activity by 100 calories expended daily is estimated to lead to a 10-pound weight loss over five years. Under the old assumption, it would have been closer to 50 pounds over five years. Decreasing consumption by about 100 calories will lead to a 2.5-pound weight loss over one year. Under the old assumption, it would have been closer 10 pounds in one year.
The authors of the consensus document use a 2011 Lancet study to illustrate the potential impact of their recommendation on policy research. Under the 3,500-calorie/pound assumption, a permanent 40-calorie/day reduction in energy intake resulting from taxing soda by 20 percent was predicted to lead to a 20-pound weight loss over five years. Under the more complicated assumptions recommended by this panel, the weight loss would be only four pounds over five years. While this doesn’t impact the revenue generated by such a tax, it would significantly mute the estimated impact of the tax on longer-term health or economic outcomes related to any decreased caloric consumption.
This further compounds the challenge of demonstrating the economic benefits of obesity and chronic disease prevention-oriented policies and programs on lowering health care costs. If the impact of a policy or program on weight status is now more modest, then the benefits of policies and programs relative to their costs will also be smaller. Knowing that prevention already doesn’t look attractive under the 10-year time horizons currently used by CBO to score potential legislation, prevention will look even less like a good deal.
The bottom line: marginal changes to diet or physical activity when made in isolation will not be impactful on weight. The impact comes from making a series of permanent, small changes to overall diet and physical activity. There is no one magic policy bullet to solve the epidemic of obesity and chronic disease, and no one food or beverage responsible for it. The way we live our lives and the way we eat has changed significantly over the past 50 years, and unless we are prepared to make holistic, permanent changes to our diets and lifestyles, the epidemic of obesity and chronic disease will not go away.