Examining the Causes and Effects of Obesity

A New Study Explores Obesity and Excess Weight Gain Among Nurses Over a 40-Year Period

Obesity is clearly one of the biggest health issues in America today, not just because of the number of Americans who suffer from being overweight or obese, but because of the myriad adverse health consequences that obesity can fuel. Moreover, the struggle to control obesity is in a very real sense a struggle with the modern American experience, as it is fundamentally linked to the way we eat, drink, sleep, recreate, and work.

So what do we know about obesity and its effects? In one recent study, “Determinants and Consequences of Obesity,” published in the September 2016 issue of the American Journal of Public Health, researchers examined data obtained through the Nurses’ Health Studies (NHS) biannual research surveys, which began in 1976 with over 120,000 female nurses and added over 116,000 younger nurses in 1989, in order to track weight changes among the participants over time, isolate obesity risk factors, and examine the extent to which weight gain increased the risk of certain diseases or otherwise negatively impacted the quality of life.

According to these researchers, when the NHS began collecting information in 1976, about 25% of women in America were classified as overweight, defined as having a body mass index (BMI=weight in kilograms divided by the square of height in meters) between 25 and 30, while an additional 17% were classified as obese, having a BMI greater than 30. By 1989, the prevalence of obese women was almost equal to those classified as overweight, with the two categories reaching about 50% of the female population. In 2016, about two-thirds of American women are classified as overweight or obese. Specifically among participants in the NHS surveys, the average weight gain over the course of the survey period was about .4 kilograms per year (1 kilogram=2.2 pounds).

Obesity Risk Factors

The authors of this particular study examined four categories of risk factors that influenced weight gain among the survey participants: dietary factors; physical activity and sleep patterns; genetics and gene-lifestyle interactions; and environmental factors.

Consistent with other studies, their data on dietary factors showed a positive association between increased consumption of animal, saturated, and trans fats and weight gain, even though increased consumption of monounsaturated and polyunsaturated fats showed no association. Data from the study also showed that those women with increased whole grain or dietary fiber consumption gained less weight, while those with increased refined grain intake gained more weight. In general, regular consumption of foods such as potato chips, french fries, processed meats, and unprocessed red meats showed a strong correlation with weight gain, while regular consumption of fruits, vegetables, whole grains, nuts and yogurt was associated with no weight gain and even weight loss.

Increased intake of sugar-sweetened beverages and fruit juices was associated with weight gain, while increased intake of water, coffee without sugar, and diet beverages was associated with weight loss. Women who were light to moderate drinkers of alcoholic beverages were less likely to gain weight than were women who were heavy drinkers or nondrinkers.

As expected, the NHS surveys also showed that physical activity plays a key role in preventing weight gain. Women with more than 30 minutes of physical activity a day showed significantly less weight gain than women with less than 30 minutes a day, with jogging or running showing the best results. Even 2-hour daily increments of standing or walking showed a 9% lower risk of obesity, and an hour of daily brisk walking lowered the risk by 24%. Conversely, 2 hours daily of a sedentary activity such as watching television increased the risk of becoming obese by up to 30%.

Sleep patterns also had a noticeable impact on weight gain. Measured over a 16-year period, the study found that women who got 5 or less hours of sleep per night were 32% more likely to gain 15 kilograms or more, and those who got 6 hours were only 12% more likely to gain that amount, than were women who slept 7 to 8 hours per night. Women with more years of rotating night shift work, resulting in less nighttime rest, showed an increased risk of weight gain and obesity.

The study also showed that some of these same lifestyle choices combined with genetic markers indicating a predisposition to obesity resulted in “exponentially higher risks of obesity.” Thus, for example, a genetic predisposition for obesity combined with a higher consumption of sugar-sweetened beverages or fried foods resulted in a higher obesity risk than in women without the genetic predisposition, while healthier lifestyle choices helped to mitigate the genetic risk.

Certain environmental factors also showed a correlation with weight gain or loss. Byproducts of exposure to plastics and other consumer goods, as measured by higher urinary concentrates of metabolites of bisphenol A and phthalates, were associated with increased weight gain among the survey participants. Other environmental factors such as urban density also played a role. For example, those women who lived in higher density areas were more likely to have lower BMIs and reported greater participation in physical activities such as walking, bicycling, and running than did women living in lower-density areas.

Weight Gain and Morbidity

As expected, the survey data reinforced that excess weight gain and obesity increased the risks of suffering from major chronic health conditions. For example, substantial weight gain after the age of 18 was a strong risk factor for Type-2 diabetes, while weight loss of 5 kilograms or more after the age of 18 lowered the risk of contracting diabetes by 50%. In addition, body fat distribution provided an additional predictor for diabetes. Women with a waist-to-hip ratio of .88 or more demonstrated more than 3 times the risk of diabetes than women with a ratio that was less than .72. Similarly, women with a waist circumference of 38 inches or more demonstrated 6 times the risk of diabetes than women with a waist measurement that was less than 28 inches.

Excessive weight gain also had a negative impact on circulatory health. Weight gain came with a higher risk of hypertension, while weight loss over the long term came with a reduced risk. The risk of coronary heart disease also increased with weight gain. The authors noted that in one 8 year sample, compared with participants who had a BMI less than 21, women with a BMI that was 29 or higher demonstrated more than 3 times the risk of heart disease after adjusting for age and smoking status. After adjusting for conditions such as hypertension and diabetes, the risk was still twice as high. Similarly, compared to those women who stayed within 3 kilograms of their age-18 weight, women who gained 10 kilograms or more after age 18 showed a 60% higher risk of heart disease. As with diabetes, higher waist-to-hip ratios were associated with a significantly higher risk of heart disease, even among women who fell within the “normal” weight categories. Higher BMIs and weight gain also increased the risk of stroke, with those women having a BMI of 27 or more demonstrating a 42% higher risk of stroke than women with a BMI that was less than 21.

Higher BMIs were also associated with a higher risk of cancer. For example, in measuring breast cancer risks in postmenopausal women, weight gains of 10 kilograms or more after menopause came with a higher risk of cancer, while risks were reduced in women who lost similar amounts during that period. Women in the heavier weight categories were also at higher risk for other types of cancer, such as cancer of the colon, endometrial cancer, and cancer of the kidney and pancreas.

In addition to these specific chronic health conditions, obese women participating in the surveys reported lower levels of “physical functioning and vitality” than did women with BMIs between 21 and 23, and regardless of baseline weight, women gaining 2.25 kilograms or more were more likely to report decreased physical functioning and vitality and increased bodily pain. The study also noted a bidirectional relationship between obesity and depression. Being overweight or obese was also one of the highest risk factors for premature death.

Conclusions

The data from this particular study reinforces some common sense conclusions about excess body weight and obesity: while some weight gain may be expected throughout life, too much weight gain is both physically and emotionally unhealthy. However, there are lifestyle choices that can be made that can reduce weight gain and the health risks that can accompany it. Eating and drinking healthier by reducing intake of processed grains, fried foods, sweetened drinks, and red meat, and replacing those with more fruits, vegetables, nuts, whole grains, and water or unsweetened drinks, has been shown to be an effective way to minimize weight gain. We also need to engage in more physical activities, even if only moderately, sit less, and get a healthy amount of sleep.

Easier said than done? Perhaps. Schools could have a positive impact by providing healthier lunches, removing tempting but unhealthy snack foods, and teaching better nutritional habits. Changing the habits of large groups of adults is trickier, but employers could assist by changing the content of vending machines to remove unhealthy snacks and drinks and replace them with healthier alternatives. Employers could also encourage employees to stand for portions of the workday rather than sit, and provide workspaces that would accommodate this. Providing exercise facilities is another alternative, especially for larger employers. The long-term health benefits could more than offset the short-term costs.

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