The United States has enjoyed a trend of steadily improving age-adjusted population mortality over the past 80 years. However, two epidemics, obesity and opioid drug abuse, are threatening the extension of that trend. This issue of Housecalls addresses some aspects of the obesity epidemic.
In adults obesity is defined by Body Mass Index (BMI) (See Table 1). BMI, is calculated with either of the following formulas: BMI = weight in kilograms / height in meters1 or weight in pounds / height in inches2 x 703.
Table 1 - Classification of Obesity in Adults
|Overweight||25 - 29.9|
|Obesity Class 1||30 - 34.9|
|Obesity Class 2||35 - 39.9|
|Obesity Class 3||> 40 (severe, extreme, massive)|
It is no secret that the US and Canadian populations have been becoming more obese over time. State by state data from the Center for Disease Control shows that the proportion of obese individuals has risen dramatically between 1994 and 2014 (Figure 1).
Figure 1 - Percent of obese adults on a state-by-state basis
And recent data from the National Health and Nutrition Examination Survey (NHANES) study reveals that the adult overall age-adjusted rate of obesity was 37.7%. It was 35% in men and 40.4% in women. The prevalence of Class 3 obesity was 7.7% overall, 5.5% in men and 9.9% among women.
The causes for these trends are many but in the end come down to changes in exercise and diet. Several factors may be driving this trend, one being decreased activity due to "screen time".
Television, computers, smart phones, videogames and tablets are everywhere. Whereas children and adults used to socialize with friends by going out and possibly playing a sport, now they can socialize online while playing the same videogame or connect through social media. Television watching has a double adverse effect on obesity risk as it is usually sedentary and the hands are free to snack, so binge-watching may also be having an effect.
The "urbanization" of the population has reduced yard work and outside spaces for physical activity, while labor saving devices like robotic vacuums and electric screwdrivers have reduced indoor activity. Small, five- to 10-minute differences in daily moderately vigorous activity can make large differences in obesity risk.
Another effect of electronics may be reduced sleep. Studies have shown that the percent of the population sleeping fewer than seven hours per night has increased from 16% to 37% over the past 40 years. And medical studies have found that sleep deprivation is associated with an increased appetite and craving for calorie-dense foods.
Diet may also contribute to sleep deprivation as studies have shown that individuals who sleep five hours or fewer per night are more likely to consume large amounts of soda with the additional hazard of increased calories.
Studies have also shown that "the increased supply of cheap, palatable, energy-dense foods" combined with improvements in distribution and accessibility are more than enough to explain the rise in obesity among populations.
While genetics may play a role in a small percentage (<5%) of cases of obesity, other interesting influences such as metabolic programming are also in play. For example, obese mothers are more likely to produce obese offspring, but if the mother has bariatric surgery and loses weight, subsequent offspring are less likely to be obese.
Regardless of the cause, the consequences of obesity are well documented. A large recent meta-analysis combined data on more than 10.5 million participants from 239 prospective studies done on four continents. A subset of almost four million participants were nonsmokers without chronic diseases and were followed for a median 13.7 years. The first five years of follow-up were excluded to avoid the influence of occult disease. The calculated hazard ratio for death by sex plotted against the BMI is in Figure 2. The reference or lowest mortality was seen with a BMI of 22.5-25.
Figure 2 - Hazard Ratio for Deaths from All Causes Plotted Against BMI by Sex
The study also looked at association of BMI with death by major underlying cause. Four major diseases stood out. Per 5 kg/m2 excess BMI, the Hazard Ratio for coronary heart disease death was 1.42, for stroke was 1.42, for respiratory disease was 1.38 and for cancer was 1.19.
Solutions to the obesity epidemic are not easy. Public health efforts in nutrition education and encouraging exercise can be moderately successful. Efforts are needed to assure delivery of the proper types of fresh foods to the populations most at risk for obesity.
The body naturally resists weight loss such that a previously obese person needs to consume 15% fewer calories to maintain weight loss than the average non-obese person consumes. This effect can persist for years after weight loss. Medications and bariatric surgery can be used when the complications of obesity manifest but appear inadequate on a population level.
Most worrisome, childhood obesity has also been on the increase over the past few decades, and it presents its own unique issues. Dr. Rosace discusses a case of juvenile obesity and how to approach it.