American adults gain lots of weight over time
Weight gain predicts poor health outcomes
Has the weight gain of American adults increased the prevalence of obesity over the first 18 years of the 21st Century? Researchers at the National Center for Health Statistics used data from nine waves of the nationally representative National Health and Nutrition Examination Survey to find out. The study defined obesity as a body-mass index of 30 or greater and severe obesity as a body-mass index of 40 or greater. Alas, the prevalence of obesity rose from 30.5 to 42.3 percent. The prevalence of severe obesity rose from 4.7 to 9.2 percent during this period. Given the links between obesity and major chronic diseases, the trend of increasing obesity portends more medical problems for Americans.
Shelter-in-place orders during the COVID-19 pandemic typically required Americans to limit their out-of-home travel to essential activities. Evidence suggests that we responded with less physical activity and more snacking. Would these behaviors lead to weight gain? Researchers at the University of California – San Francisco analyzed data from an ongoing longitudinal study in which 269 participants periodically reported their weight. From February 1 to June 1, 2020, each participant gained an average of 1.8 pounds per month or 7 pounds during the four months. Reduced physical activity and poor eating habits can lead quickly to weight gain. Of course we already knew this! It behooves us to develop habits that predispose us to Keep Moving and Eat Better,
Most Americans gain weight from early- to middle-adulthood. Such weight gain predicts increased risk of adverse health outcomes. Researchers at Harvard used data from two large prospective cohorts, the Nurses’ Health Study, and the Health Professionals Follow-up Study, to evaluate the risks of chronic conditions from age 18 years (for women) and age 21 years (for men) up to age 55 years. Over a median follow-up of 37 years, women gained a median of 24 pounds of body weight. Over a median follow-up of 34 years, men gained a median of 21 pounds.
After adjusting for multiple confounding factors and compared to participants with stable weight (plus or minus 5.5 pounds), increased weight of 5.5-22 pounds predicted significantly increased risk of multiple chronic conditions, including type 2 diabetes, gall stones, hypertension, cardiovascular disease, obesity-related cancers, and severe osteoporosis. Weight gain of more than 22 and 44 pounds predicted significantly greater risk of mortality in women and men, respectively. Type 2 diabetes showed the greatest increase in risk with weight gain, especially at weights indicating obesity. Increased weight gain also predicted significantly reduced likelihood of achieving a composite healthy aging outcome (no self-reported history of major chronic diseases, no cognitive decline, no physical limitations). The risk of showing a composite poor health outcome of type 2 diabetes, cardiovascular disease, cancer, and non-traumatic death increased step-wise beyond a weight gain of 22 pounds. Thus, weight gain of 22 pounds or more during adulthood limited women’s and men’s prospects for healthy aging.
The prevalence of diabetes among US adults rose significantly during the past three decades. The concomitant rise in obesity accounted for most of the increase in diabetes. Researchers used data from the National Health and Nutrition Examination Survey (NHANES) to determine how weight-change from early adulthood to midlife related to the risk of developing diabetes. Participants self-reported their weight at age 25 and 10 years before they enrolled in NHANES. Body weight was measured during 10 years of follow-up in NHANES. Body-mass index values (BMI) were calculated from weight and height. Four categories of changes in BMI values were used to capture weight change over the participants’ life course: 1) stable non-obese, 2) losing weight, 3) gaining weight, and 4) stable obese.
During 10 years of follow-up and compared to participants in the stable obese category, those in the stable non-obese category had 78 percent lower risk of developing diabetes. Similarly, those in the losing category (who went from obese to normal-weight BMI) had 67 percent lower risk of developing diabetes. Analyses showed that 64 percent of the diabetes cases that occurred during follow-up could theoretically have been avoided if all participants had maintained normal-weight BMI from young adulthood through midlife. Given the potential complications of diabetes (kidney disease, peripheral nerve damage, retinal damage, amputations) and the enormous medical care cost of diabetes, maintaining normal weight can greatly improve Quality of Lifespan.
Would weight gain during young- to middle-adulthood predict increased risk of death? Researchers crunched data for 36,051 participants in the National Health and Nutrition Examination Surveys (NHANES) for years 1988-1994 and 1999-2014 to find out. Three categories of weight expressed in terms of body-mass index (BMI) included: 1) underweight and normal weight (BMI < 25), 2) overweight (BMI 25.0-29.9), and obese (BMI > 30). Participants recalled their body weight at age 25 and 10 years before baseline at the first NHANES baseline survey, at which time body weight was measured. Participants gained an average of 29.5 pounds from age 25 to the first NHANES survey. Of that, participants gained an average of 19.4 pounds from age 25 to 10 years before baseline (that is, from early- to middle-adulthood).
After adjusting for confounding factors and compared to stable normal weight participants from age 25 to baseline (that is, over the entire adulthood), those who moved from stable normal weight to obese and those who were stable obese during the entire period had significant 22 and 72 percent higher risks, respectively, of dying of any cause. Similarly, participants who were stable obese during the entire period had significant 49 and 143 percent higher risks, respectively, of dying or developing heart disease. Curiously, participants who lost weight and transitioned obese to non-obese from 10 years before the baseline to baseline (that is, from middle-to late adulthood) had significant 30 and 48 percent higher risks, respectively, of dying or developing heart disease. The key message: Maintaining normal body weight over your adult lifespan may reduce your risk of dying prematurely or having heart disease.
Would the trajectory of body weight of American adults over the past decades affect the risk of mortality over the life course? Researchers used data from 4,576 participants in the original cohort and 3,753 participants in the offspring cohort of the Framingham Heart Study to find out. Height and weight data (used to calculate body-mass index - BMI) were collected at multiple times during follow-up. Four BMI categories were created for individuals from age 31 to 80 years: 1) normal, 2) overweight, 3) class I obese, and 4) class II / III obese. During follow-up, the proportions of individuals with class I and class II / III obesity increased from 12.4 to 16.1 percent and from 3.2 to 6.2 percent respectively, from the original to offspring cohort.
Seven BMI trajectories were also created. Participants in the original cohort who exhibited the normal weight upward trajectory (in which BMI increased over time but stayed in the normal range of 18.5-24.9) had significantly lower risk of mortality than all other trajectories – even compared to normal weight stable or lower level of normal weight or overweight downward. The two trajectories of obesity had the highest risks of mortality. For the offspring cohort, the risk of mortality for participants in the normal weight upward trajectory was not significantly different from those in the normal weight stable or lower level of normal weight or overweight to obesity trajectories. Thus, single measures of BMI (except perhaps for those persons with severe obesity) do not adequately predict mortality risk. The increase of BMI over time appears to be more important. Do yourself a favor and maintain a healthy body weight as the years go by.