Key Points

Question What were the trends in current measured body mass index and weight, self-perceived weight status, weight loss attempts, and weight loss strategies in adults in the United States from 1999 to 2016?

Findings In this cross-sectional study with data from 48 026 participants in the National Health and Nutrition Examination Survey, increasing trends were observed in current measured body mass index and weight; adjusted, self-reported, prior-year weight; and the difference between current measured weight and adjusted, self-reported, prior-year weight. The proportion of participants who attempted to lose weight increased during the study period.

Meaning In this study, an increased trend in the proportion of participants who attempted to lose weight was observed, despite increased trends in current and historical weight.

Abstract

Importance The self-perception of weight and weight loss attempts might promote weight loss and maintenance.

Objective To examine trends in current measured body mass index (BMI) and weight, self-reported weight, self-perceived weight status, weight loss attempts, and weight loss strategies among adults in the United States.

Design, Setting, and Participants This national cross-sectional study used data from continuous National Health and Nutrition Examination Survey (NHANES) data sets (1999-2000 to 2015-2016). Participants were US residents older than 20 years. Data were analyzed from January 2018 to December 2018.

Main Outcomes and Measures Current measured BMI and weight, self-reported weight, self-perceived weight status, weight loss attempts, and applied weight loss strategies. Adjusted, self-reported, prior-year weight was calculated using correction equations that considered age, sex, race/ethnicity, and quartile of self-reported prior-year weight.

Results Data were collected from 48 026 participants (19 792 [41.2%] aged 40-64 years; 24 255 [50.5%] women; 21 725 [45.2%] white) through 9 surveys from 1999-2000 to 2015-2016. Increasing trends were observed in current measured BMI (difference, 1.20; 95% CI, 0.92-1.47; P for trend < .001), current measured weight (difference 2.77 kg; 95% CI, 1.92-3.61 kg; P for trend < .001), adjusted, self-reported, prior-year weight (difference, 2.36 kg; 95% CI, 1.52-3.21 kg; P for trend < .001), and the difference between measured and adjusted self-reported weight (difference 0.70 kg; 95% CI, 0.34-1.07 kg; P for trend < .001). During this period, the proportion of overall participants who had attempted to lose weight increased from 34.3% to 42.2% (difference, 8.0%; 95% CI, 4.1%-10.5%; P for trend < .001). The most commonly reported weight loss strategies with the most rapidly increasing prevalence during the study period were reduced food consumption (21.2%-31.9%; difference, 11.1%; 95% CI, 8.2%-13.3%; P for trend < .001), exercise (18.2%-31.5%; difference, 14.4%; 95% CI, 11.3%-16.9%; P for trend < .001), and frequent water intake (0.2%-26.3%; difference, 26.2%; 95% CI, 24.1%-29.0%; P for trend < .001). Between 2005-2006 and 2015-2016, increases were also observed for the reported consumption of more fruits, vegetables, and salads (0.1%-29.4%; difference, 30.3%; 95% CI, 28.1%-31.2%; P for trend < .001), changing eating habits (0.3%-20.5%; difference, 20.2%; 95% CI, 19.1%-22.3%; P for trend < .001), and the consumption of less sugar, candy, and sweets (0.2%-20.9%; difference, 21.7%; 95% CI, 19.3%-22.6%; P for trend < .001).

Conclusions and Relevance In this cross-sectional study, our data indicated an increasing trend in the proportion of participants who attempted to lose weight and a parallel increasing trend in current measured BMI and weight among adults in the United States.

Introduction

Obesity is associated with a variety of major chronic diseases, including cardiovascular disease, type 2 diabetes, and cancer, as well as premature mortality.1,2 Compelling evidence suggests that even moderate (ie, 3%-5%) weight loss significantly reduces the risk of obesity-related diseases and mortality.3 However, losing weight and maintaining a healthy weight remain significant challenges.4

Previous studies have shown that self-perception of weight and weight loss attempts might promote weight loss and maintenance.5,6 In addition, the application of weight loss strategies has been associated with successful weight loss in adults with obesity in the United States.7 However, nationwide data regarding trends in current measured body mass index (BMI; calculated as weight in kilograms divided by height in meters squared) and weight, self-reported weight, self-perceived weight status (eg, self-perceived weight and the intention to weigh more, less, or the same amount), weight loss attempts, and weight loss strategies in the adult population in the United States are scarce.

Using nationally representative data from 9 continuous applications of the National Health and Nutrition Examination Survey (NHANES; 1999-2000 to 2015-2016), we aimed to estimate temporal trends in current measured BMI and weight, self-reported weight, self-perceived weight status, and attempts and strategies used for weight loss among adults in the United States. We also examined the trend in adjusted, self-reported, prior-year weight using a corrected equation.8 Trends in weight loss strategies among those who had overweight or obesity or perceived themselves as having overweight or obesity were also analyzed. We also focused on the weight differences between the last and current years to determine whether those who attempted to lose weight and used different strategies successfully lost weight.

Methods

Study Design and Population

The NHANES is a national series of cross-sectional and multistage probability surveys representative of the noninstitutionalized population of the United States.9 Data in NHANES have been collected continuously in 2-year surveys since 1999. We used data from 9 consecutive surveys, covering the period of 1999-2000 to 2015-2016. We restricted our analyses to nonpregnant participants 20 years or older. The NHANES was approved by the National Center for Health Statistics Ethics Review Board. All participants provided informed consent. The Medical School of Ningbo University institutional review board determined that the current study was exempt from review and informed consent given the use of publicly available data. This study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline for cross-sectional design.

The NHANES collects data through home interviews and physical examinations. During home interviews, participants were asked questions about demographic, socioeconomic, dietary, and health-related parameters. The detailed methodology and protocols are available on the NHANES website.9

Assessment of Self-perceived Weight Status and Weight Loss Attempts and Strategies

A weight history questionnaire was administered to participants 16 years and older during household interviews. This questionnaire solicited personal data about several topics related to body weight, including self-reported weight (ie, self-reported weight over a lifetime), self-perceived weight status (ie, “how do you consider your weight” and whether participants intend to weigh more, less, or the same amount), weight loss attempts during the past year (ie, “during the past 12 months, have you tried to lose weight”), and applied weight loss strategies (eg, reduced food intake).

Self-reported weight was recorded for current weight, prior-year weight, weight 10 years earlier, weight at age 25 years, and highest-ever weight. Measured weight was measured in pounds using electronic scales in the mobile examination center. Self-reported current and previous weights were standardized to weight in pounds using a conversion factor of 2.2046 pounds per kilogram. In this study, current measured weight was converted from pounds to kilograms using the same conversion formula.

Self-perceived weight status was estimated from participant response to the question, “How do you consider your weight?” (possible responses, overweight, underweight, or approximately the right weight) and to the item inquiring whether the participant intends to weigh more, less, or the same amount. Other questions, such as, “During the past 12 months, have you tried to lose weight?” addressed weight loss attempts. Participants whose self-reported current weight was at least 10 pounds lower than their reported prior-year weight were asked whether that weight change had been intentional. Those who answered yes were categorized as having tried to lose weight. All other participants, including those who reported an unintentional weight loss of at least 10 pounds, were asked directly, “During the past 12 months, have you tried to lose weight?”10

Participants who reported a weight loss attempt during the previous year were asked to provide further details about applied strategies. From 1999-2000 to 2015-2016, the NHANES provided a list of 14 to 20 options. The following 14 options were included in all surveys: (1) reduced food intake, (2) switched to less caloric foods, (3) reduced fat intake, (4) exercised, (5) skipped meals, (6) consumed diet foods or products, (7) used a liquid diet formula, (8) participated in a weight loss program, (9) used prescription diet pills, (10) used nonprescription diet pills, (11) used laxatives or vomiting, (12) consumed large volumes of water, (13) adhered to a special diet, or (14) other. Starting in 2005, the NHANES survey included 6 additional options, as follows: (1) reduced carbohydrate intake; (2) began or resumed a smoking habit; (3) increased intake of fruits, vegetables, and salads; (4) altered eating habits (eg, no food consumption late at night, several small meals per day); (5) reduced intake of sugar, candy, and sweets; and (6) reduced consumption of junk food or fast food. The strategies were not mutually exclusive.

The above questions were presented to participants 16 years and older. Participants 85 years and older were top-coded at 85 years of age. Data about several demographic parameters were collected, including age (ie, 20-39, 40-64, and ≥65 years), sex (ie, male and female), race/ethnicity (ie, non-Hispanic white, non-Hispanic black, Mexican-American, and other), and BMI (ie, normal weight, 18 to <25; overweight, 25 to ≤30; and obesity, ≥30).

Statistical Analysis

Prevalence estimates and SEs were calculated using the procedure proc surveymeans. Calculations with SEs of 30% or less were considered reliable.11 If the relative SE exceeded 30%, data were suppressed (empty cells), consistent with NHANES reporting guidelines.12

For continuous variables, linear trends across each survey were calculated using the procedure proc surveyreg after adjusting for age, sex, and race/ethnicity. For categorical variables, trends across each survey were calculated by including the midpoint of each survey as a continuous variable in the logistic regression after adjusting for age, sex, and race/ethnicity. A Taylor series linearization was used to estimate variance.11

Odds ratios (ORs) and 95% CIs were calculated using the procedure proc surveylogistic, and the prevalence ratios are presented. Increasing trends were defined as differences greater than zero or ratios greater than 1, with P for trend ≤ .001; decreasing trends were defined as differences less than 0 or ratios less than 1, with P for trend ≤ .001; and stable trends were defined as P for trend > .001.

To reduce type I error induced by multiple tests, Bonferroni correction was applied; P ≤ .001 was adopted as the threshold for statistical significance, and all tests were 2-tailed. All statistical analyses were performed using SAS statistical software version 9.4 (SAS Institute) and designed to account for the complex weighted sampling design of the NHANES.9

Results

Data were collected from 48 026 participants (19 792 [41.2%] aged 40-64 years; 24 255 [50.5%] women; 21 725 [45.2%] white) through 9 surveys from 1999-2000 to 2015-2016. The characteristics of the participants are summarized in the eFigure and eTable 1 in the Supplement. The sample sizes stratified by age, sex, race/ethnicity, and BMI are also shown in eTable 1 in the Supplement. Participants’ weight 10 years earlier, weight at age 25 years, highest-ever weight, and age of highest-ever weight appear in eTable 2 in the Supplement.

From 1999-2000 to 2015-2016, significant increases in current measured BMI (difference, 1.20; 95% CI, 0.92-1.47; P for trend < .001), current measured weight (difference 2.77 kg; 1.92-3.61 kg; P for trend < .001), adjusted, self-reported, prior-year weight (difference, 2.36 kg; 95% CI, 1.52-3.21 kg; P for trend < .001), and the difference between current measured weight and adjusted, self-reported, prior-year weight (difference 0.70 kg; 95% CI, 0.34-1.07 kg; P for trend < .001) were observed (Table 1). Among those who attempted to lose weight, increased trends were observed for current measured BMI (difference, 1.21; 95% CI, 0.69-1.73; P for trend < .001), current measured weight (difference, 2.55 kg; 95% CI, 0.93-4.17 kg; P for trend < .001), and the difference between current measured weight and unadjusted, self-reported, prior-year weight (difference 0.55 kg; 95% CI, 0.37-0.86 kg; P for trend < .001) (Table 1). Among those who did not attempt to lose weight, an increasing trend was observed for the difference between current measured weight and adjusted, self-reported, prior-year weight (difference, 0.85 kg; 95% CI, 0.45-1.25 kg; P for trend < .001) (Table 1). The weighted prevalence of overall participants who attempted to lose weight during the previous year increased from 34.3% in 1999-2000 to 42.2% in 2015-2016 (difference, 8.0%; 95% CI, 4.1%-10.5%, P for trend < .001) (Table 2).

Table 3 presents the trends in weight loss strategies among participants who attempted to lose weight during the previous year. From 1999-2000 to 2015-2016, the most commonly applied strategies were reduced food consumption (eg, 30.8% [95% CI, 29.2%-32.4%] of participants in 2005-2006 and 31.9% [95% CI, 30.1%-33.8%] of participants in 2015-2016), exercise (eg, 29.5% [95% CI, 27.1%-31.8%] of participants in 2005-2006 and 31.5% [95% CI, 28.7%-34.3%] of participants in 2015-2016), and consumption of a large volume of water (eg, 21.6% [95% CI, 19.1%-24.0%] of participants in 2005-2006 and 26.3% [95% CI 23.9%-28.7%] of participants in 2015-2016). The proportion of overall participants who reported reduced food consumption as a weight loss attempt increased from 21.2% to 31.9% during the study period (difference, 11.1%; 95% CI, 8.2%-13.3%; P for trend < .001). The proportion of overall participants who reported exercise as a weight loss strategy increased from 18.2% to 31.5% (difference, 14.4%; 95% CI, 11.3%-16.9%, P for trend < .001). The proportion of overall participants who reported consumption of a large volume of water increased from 0.2% to 26.3% (difference, 26.2%; 95% CI, 24.1%-29.0%; P for trend < .001). From 2005-2006 to 2015-2016, significantly increased trends were also observed in the proportions of overall participants who reported consuming more fruits, vegetables, and salads (0.1%-29.4%; difference, 30.3%; 95% CI, 28.1%-31.2%; P for trend < .001); changing their eating habits (0.3%-20.5%; difference, 20.2%; 95% CI, 19.1%-22.3%; P for trend < .001); consuming less sugar, candy, and sweets (0.2%-20.9%; difference, 21.7%; 95% CI, 19.3%-22.6%; P for trend < .001); or consuming less junk food or fast food (12.8%-24.3%; difference, 12.1%; 95% CI, 10.1%-14.5%; P for trend < .001).

Table 4 shows the cross-tabulated analyses of current measured BMI and self-perceived weight status. Among those who had overweight or obesity, a decreased trend was observed for the proportion of participants who considered themselves as having overweight, whereas an increased trend was observed for the proportion of participants who considered themselves as having underweight or about the right weight (difference, 3.3%; 95% CI, 1.0%-5.6%; P for trend < .001) (Table 4).

Table 5 presents the cross-tabulated analyses of current measured BMI with self-perceived weight status among US adults who pursued weight loss strategies. Among those with a BMI of at least 25 who considered themselves as having overweight, we observed increased trends for attempting to lose weight by eating less food (11.3%; 95% CI, 8.5%-14.1%; P < .001); exercising (18.1%; 95% CI, 15.4%-20.8%; P < .001), and drinking a lot of water (37.8%; 95% CI, 35.7%-40.0%; P < .001).

Discussion

This analysis of nationally representative data collected from US adults during NHANES 1999-2000 through NHANES 2015-2016 revealed increasing trends in current measured BMI and weight; adjusted, self-reported, prior-year weight; and the difference between current measured weight and adjusted, self-reported, prior-year weight. The prevalence of participants who tried to lose weight in the past year also increased over time. Overall, reduced food consumption, exercise, and consumption of a large volume of water were the most frequently applied weight loss strategies. In addition, the proportion of participants who reported consuming more fruits, vegetables, and salads, changing their eating habits, consuming less sugar, candy, and sweets, or consuming less junk food or fast food increased sharply over time and became the most commonly applied weight loss strategies in recent years.

From 2007-2008 to 2015-2016, the prevalence of obesity among US adults increased from 33.7% to 39.6%.1 We also observed increasing trends in actually measured BMI and weight and self-perceived weight status from 1999-2000 to 2015-2016 in parallel with the increasing proportion of participants who tried to lose weight.

Unsurprisingly, among those who had overweight and obesity and pursued weight loss strategies, we observed an increased trend in the proportion of participants who considered themselves as having overweight. However, evidence suggests that a self-perception of having overweight is not reliably associated with physical activity or healthy eating.5 In addition, much evidence has implied that self-perceived overweight was associated with increased weight gain over time.5

Additionally, a previous study emphasized that less than 34% of the US population reported attempted weight loss in response to an inquiry.13 Social pressure associated with an acceptable body weight and size might contribute to the increased reporting of weight loss attempts.14 Despite the weighted prevalence of participants who attempted to lose weight in the past year increasing from 34.3% to 42.2% during the study period, we observed increased trends for current measured BMI and weight and the difference between current measured weight and self-reported, prior-year weight among those had attempted to lose weight in the past year. Taken together, these findings suggest that although 34.3% to 42.2% of adults in the United States in our study reported weight loss efforts, many of them might not have actually implemented weight loss strategies or applied a minimal level of effort, which yielded unsatisfactory results.

Although reduced food consumption was among the most commonly reported strategies by participants who attempted to lose weight, no significant trends were observed for the proportion of participants who reported lowering calories, implying that energy intake was not decreased. Furthermore, reduced food consumption might be a general strategy applied by adults in response to social pressure, despite evidence supporting the association of reduced food (ie, calorie) consumption and significant weight loss.15,16 However, adherence to such modified diets, which is the best predictor of success in any dietary modification, is very difficult to maintain.17 Exercising was another of the most commonly reported strategies by participants who attempted to lose weight; however, a 2008 study18 reported that while 65% of adults in the United States reported that they met the recommended levels of physical activity, only 5% actually met these goals as objectively measured using accelerometry devices. Furthermore, a 2018 statement from the American Heart Association19 indicated that 8 in 10 adults in the United States did not satisfy the guidelines for aerobic and muscle-strengthening exercise. Therefore, decreased energy intake, adherence to reduced food consumption, and the quality of exercise are significant challenges to effective weight loss. An increasing trend in the use of reduced food consumption as a weight loss strategy was evidenced in the proportion of participants in our study; however, no significant change over time was observed in the proportion of overall participants who reported lowering calories or reducing carbohydrate consumption to lose weight.

Our analysis revealed an increasing trend in the use of increased water consumption as a weight loss strategy. This increase can be attributed to convincing evidence regarding the potentially important role of water in reducing energy intake, which thus contributes to the long-term maintenance of weight loss.20

From NHANES 2005-2006 to NHANES 2015-2016, the proportion of participants who reported consuming more fruits, vegetables, and salads, changing their eating habits, consuming less sugar, candy, and sweets, and consuming less junk food or fast food increased sharply. The sharp increase might be partly because these categories were added to NHANES in the 2005-2006 cycle. However, as the trends for actually measured weight and self-reported weight history increased during the same time period, these strategies may not have translated into effective weight loss.5 Evidence from other studies21 has shown these changes to be associated with less weight gain, and therefore, these strategies would be encouraged.

Only slight changes were observed in reduced fat consumption in participants during the study period; however, among adults in the United States with obesity who participated in the NHANES between 2001 and 2006, a large proportion were more likely to report a body weight loss of 10% or more in response to reduced fat consumption, increased exercise, the use of prescription weight loss medications, or participation in a commercial weight loss program.7 Existing guidelines and compelling evidence also suggest that longitudinal weight management relies on a combination of reductions in energy and fat intake, an increase in dietary fiber intake, regular physical activity, self-monitoring, and other behavioral techniques.22 Reduction of either carbohydrates or fat has been similarly related to weight loss, especially in the context of low-calorie diets.23

It is worth noting that specific dietary or lifestyle factors may independently improve weight loss and need to be targeted.21 Taken together, these findings suggest a need to increase the promotion of effective strategies for weight loss, including caloric reduction and increased physical activity, among all adults attempting to lose weight.24 Notably, adherence is the primary factor associated with a successful response to a weight loss attempt.25 Therefore, weight loss strategies that consider a participant’s preferences and abilities may help to optimize participant adherence.26

In fact, those who attempted weight loss might not be the participants who truly needed to lose weight, and others might need to lose weight but did not attempt to do so because they perceived their weight as approximately the right weight. In our study, a decreased trend was observed for the proportion of participants with overweight or obesity who considered themselves as having overweight. Among those who attempted to lose weight, we observed an increased trend for the difference between current measured weight and self-reported, prior-year weight.

Strengths and Limitations

The identified trends in current measured BMI and weight, self-perceived weight status, and weight loss attempts and strategies were determined using nationally representative data. Therefore, the results may be generalizable to other adults in the United States. In our analyses, Bonferroni correction was used to reduce the type I error. However, several potential limitations of our study should be acknowledged. First, the self-perceived weight status and weight loss attempts and strategies were based on self-reported data. However, according to our data, current self-reported weight was only slightly lower than measured weight (difference, 1.19-2.09 pounds), and the trends of these 2 measures were similar. In addition, previous studies reported a correlation of at least 90% between self-reported and actual weights,27 suggesting that the recall of weight history is relatively stable and subject to minimal bias.28 Further, we applied the corrected equation to calculate the adjusted, self-reported, prior-year weight.8 Second, the NHANES did not collect data on the frequency, duration, or number of weight loss attempts or strategies. Repeated weight loss attempts have been shown to reduce participants’ beliefs in the long-term effects of weight loss efforts.29 Third, temporal relationships and causality could not be established because of the cross-sectional design of NHANES.

Conclusions

In conclusion, our analysis of nationally representative data collected from adults in the United States who participated in the NHANES from 1999-2000 to 2015-2016 revealed increasing trends in actually measured BMI and weight; adjusted, self-reported, prior-year weight; and the difference between current measured weight and adjusted, self-reported, prior-year weight. These increases were observed despite increases in the proportion of participants who attempted to lose weight and used weight loss strategies, such as reducing food consumption, exercising, and consuming a large volume of water.

Back to top Article Information

Accepted for Publication: September 23, 2019.

Published: November 13, 2019. doi:10.1001/jamanetworkopen.2019.15219

Correction: This article was corrected on December 6, 2019, to fix errors in the title and Table 3.

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2019 Han L et al. JAMA Network Open.

Corresponding Author: Lu Qi, MD, PhD, FAHA, School of Public Health and Tropical Medicine, Department of Epidemiology, Tulane University, 1440 Canal St, Ste 1724, New Orleans, LA 70112 (lqi1@tulane.edu).

Author Contributions: Dr Qi had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Drs Han, You, and Zeng contributed equally to this paper.

Concept and design: Han, Qi.

Acquisition, analysis, or interpretation of data: You, Zeng, Feng, Astell-Burt, Duan.

Drafting of the manuscript: Han, Qi.

Critical revision of the manuscript for important intellectual content: You, Zeng, Feng, Astell-Burt, Duan.

Statistical analysis: Han, You, Duan.

Administrative, technical, or material support: Duan.

Supervision: Zeng, Duan, Qi.

Conflict of Interest Disclosures: None reported.

Funding/Support: This study was supported by grants HL071981, HL034594, and HL126024 from the National Heart, Lung, and Blood Institute, grants DK115679, DK091718, DK100383, and DK078616 from the National Institute of Diabetes and Digestive and Kidney Diseases, grant KD46200 from the Boston Obesity Nutrition Research Center, award number PPXK2018-02 from Ningbo Health Branding Subject Fund, grants 2017YFC1310902 and 2018YFC1315305 from the National Key Research and Development Program of China, grant SZSM201803080 from the Sanming Project of Medicine in Shenzhen, grants 81602853 and 81960592 from the National Natural Science Foundation of China, grant LY17H260002 from the Natural Science Foundation of Zhejiang Province, and grant 201803 from the K.C. Wong Magna Fund in Ningbo University, Zhejiang Key Laboratory of Pathophysiology. Dr Astell-Burt was supported by leader fellowship number 1140317 from the National Health and Medical Research Council Boosting Dementia Research, Dr Feng was supported by career development fellowship number 1148792 from the National Health and Medical Research Council, and Drs Astell-Burt and Feng were supposed by project grant 1101065 from the National Health and Medical Research Council.

Role of the Funder/Sponsor: The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.