Introduction
This chapter describes changes in body weight of obese participants who did not undergo bariatric surgery. It assesses possible body weight trajectories among obese patients who are managed in primary care and provides a context against which bariatric surgery may be compared. A target of 5% body weight loss is often recommended for obese subjects who intend to lose weight.95 In practice, access to weight-management interventions may be limited28 and systematic reviews show that weight-management interventions have only small and poorly maintained effects on body weight.29,96 In order to understand the frequency with which reductions in BMI may occur in a large population, this part of the study aimed to estimate the probability of an obese individual attaining normal body weight, or a reduction of 5% in body weight in the absence of bariatric surgery. The results of this study have been published open access in the American Journal of Public Health (© American Public Health Association).97
Results
The analysis comprised 278,982 participants, including 129,194 men and 149,788 women, who were registered between 1 November 2004 and 31 October 2014, and had three or more BMI records recorded during this period. The initial distribution of the sample by gender and BMI is shown in . Mean age was 55 years for men and 49 years for women. At the index date (date of the first BMI record in the study period) there were a minimum of 25,000 male and 23,000 female participants each for the BMI categories 18.5–24.9 kg/m2 (normal weight), 25.0–29.9 kg/m2 (overweight), 30.0–34.9 kg/m2 (obese) and 35.0–39.9 kg/m2 (severely obese). There were similarly high numbers of female participants with an index BMI of 40.0–44.9 kg/m2 (morbidly obese) but fewer male participants in this category at baseline (14,767). There were 6481 men and 18,451 women with a baseline BMI ≥ 45.0 kg/m2 (super obese).
Number of BMI records per participant and proportions showing no change, increase, decrease or weight cycling over 9 years following first BMI record
also shows the frequency and proportion of participants recorded as having no change in BMI category, increases in BMI category, decreases in BMI category or weight cycling (both increases and decreases) over 9 years following first BMI record. The number of BMI records per participant increased with baseline BMI category. The proportion of participants showing no change was greatest among participants in the normal weight category (men 57%; women 59%) and decreased with higher baseline BMI, with the exception of those initially categorised as super obese. Only 14% of all men and 15% of women showed decreases in BMI category without increases over the same period. The proportion of participants with records indicating only decreases in BMI increased with baseline BMI category, with the highest proportions observed for those initially categorised as morbidly obese (men 19%; women 19%) and super obese (men 21%; women 19%). A small proportion of participants (12% each of men and women) had only BMI category increases recorded, with the highest proportion found among those initially categorised as normal weight (men 20%; women 18%). Weight cycling was observed in over one-third of participants (35% of men; 38% of women) and was most common among severely obese (men 46%; women 47%) and morbidly obese (men 51%; women 52%) participants.
shows the frequency of transitioning to normal body weight during up to 9.9 years’ follow-up after the first BMI record. During a maximum of 9 years’ follow-up, 1283 men and 2245 women attained normal body weight records. The annual probability of achieving normal body weight was 1 in 210 for men and 1 in 124 for women with simple obesity. The probability declined with increasing BMI category. In patients with morbid obesity, the annual probability of achieving normal weight was 1 in 1290 for men and 1 in 677 for women. In women, the probability of achieving normal weight among super-obese participants was 1 in 608, similar to that observed in morbid obesity. In the smaller number of super-obese men, the probability was higher, at 1 in 362.
Annual probability of achieving normal body weight (BMI < 25 kg/m2) by initial BMI category and gender
Annual probabilities of achieving a clinically relevant 5% reduction in body weight are shown in . The annual probability of experiencing a 5% weight reduction was 1 in 12 for men and 1 in 10 for women with simple obesity. Probability increased with increasing BMI category. For patients with morbid obesity, the annual probability of achieving 5% reduction in body weight was 1 in 8 for men and 1 in 7 for women. The highest annual probability was observed among patients with super obesity (1 in 5 for men and 1 in 6 for women). However, among participants who lost 5% body weight, 52.7% (95% CI 52.4% to 53.0%) at 2 years, and 78.0% (95% CI 77.7% to 78.3%) at 5 years, had BMI records that indicated weight gain to values above the 5% weight loss threshold.
Annual probability of achieving a 5% reduction in body weight by initial BMI category and gender
Among patients with a recorded decrease in BMI category over the study period, shows the percentage of men and women whose later BMI records revealed an increase, a further decrease or no change in BMI category. The majority of patients (men 61%; women 59%) whose records showed a decrease in BMI category went on to record a subsequent increase in BMI category. These proportions were similar for men and women and across BMI categories. The proportion of patients who showed a second decrease in BMI category was highest among patients with morbid (men 16%; women 19%) and super obesity (men 23%; women 24%) and was considerably less frequent in lower BMI categories. Overweight patients and those with simple obesity were the most likely to display no further BMI category change following a recorded decrease.
Changes in BMI category following an initial decrease in BMI category. Data are presented by gender and initial BMI category.
Discussion
Summary of findings
Analysis of primary care EHRs for a large population based sample of men and women over a 9-year period revealed that the probability of obese patients attaining normal weight was very low. The annual probability of patients with simple obesity attaining a normal body weight was only 1 in 131 for women and 1 in 225 for men. The likelihood of attaining normal body weight declined with increasing BMI category, with the lowest probability observed for patients with morbid obesity. The smaller group of patients with super obesity represented a departure from this trend, but nevertheless showed a low probability of attaining normal body weight. Although the probability of patients achieving a 5% reduction in body weight was considerably higher, the majority of these patients went on to regain lost weight, as evidenced by BMI records of > 95% of the initial value, within 2–5 years of the first record that was lower than 95% of the initial value.
These findings raise questions concerning whether or not current obesity treatment frameworks, grounded in weight management programmes accessed through primary care, may be expected to achieve clinically relevant and sustained reductions in BMI for the vast majority of obese patients and whether or not they could be expected to do so in the future. The lack of sustained BMI reductions could be driven by low intervention uptake rates or their lack of effectiveness. In a previous study, we reported that weight-loss interventions are currently offered only to a minority of patients in primary care.28 Efforts are under way to improve this situation, with the proportion of patients with obesity offered multicomponent weight-loss interventions included among potential new indicators in the 2016/17 consultation for the Clinical Commissioning Group Indicator Set (CCG OIS).98 However, even when treatment is accessed, evidence suggests that behavioural weight-loss interventions focusing on caloric restriction and increased physical activity are unlikely to yield clinically significant reductions in body weight.29,99 A recent series of reviews documented the limited progress in reversing the global obesity epidemic and called for regulatory actions from governments as well as co-ordinated efforts across industry and society to reduce obesity.100–103 Dietz et al.104 warn that preventative strategies are unlikely to reduce weight in people living with severe obesity and stress the need for changes in the delivery of care for these patients. In combination with previous research, this study highlights the current failures in combating existing obesity cases at a population level.
Comparison with other results
Reductions in BMI category were observed more frequently among patients with a higher baseline BMI but these decreases were more likely to be followed by subsequent increases rather than further decreases or stability in BMI category. Weight cycling, evidenced by both increases and decreases in BMI category, was most common among men and women with baseline BMIs in the morbidly obese category. Greater instability in weight trajectories among patients with higher BMIs has been reported previously.105 Weight cycling has been linked to a higher risk of morbidity and mortality compared with stable obesity,106–108 although evidence of causality remains inconclusive.109
The higher likelihood of decreases in BMI category and of 5% weight loss among the more severely obese participants in this study is consistent with results from clinical trials110 and previous cohort studies111 in which higher BMI predicted greater weight loss. The increased probability of weight reduction among patients with more severe obesity may reflect more accurate perceptions of personal weight status112,113 and higher treatment rates among these patients. It is also possible that BMI decreases in severely obese patients reflect unintentional weight loss resulting from greater comorbidity. The finding that a high proportion of patients in this analysis experienced a period of weight regain following weight loss is also consistent with previous research. At least 50% of patients who achieved 5% weight loss were shown to have regained this weight within 2 years. It has previously been reported that approximately 80% of people who intentionally achieve weight loss ≥ 10% of their body weight will regain that weight within 1 year.114
Strengths and limitations
This analysis had the strengths of a large population-based cohort with prolonged follow-up.
Slightly lower numbers at the highest levels of BMI might have made these estimates slightly less precise. Data are presented for adults aged > 20 years. Inspection of age-specific values revealed, as expected, greater weight gain at younger ages and a somewhat greater tendency to weight loss at older ages. It was not possible to evaluate intentionality of weight loss. Previous studies have reported that the majority of obese individuals would like to lose weight and a large proportion are actively attempting to reduce their weight,115,116 so a relatively high level of intentionality among obese participants may be assumed. Additionally, monitoring of BMI among obese patients in primary care has been shown to positively predict treatment.117 Patients in the present study were required to have a minimum of three BMI measurements recorded, suggesting that an inflated proportion of patients in this sample might have been involved in and interested in weight-management interventions. Nevertheless, we acknowledge that unintentional weight loss was also included and might result from physical disorders such as cancer, or psychological concerns such as bereavement.118–120 Additional in-depth analyses might evaluate patterns of weight change in relation to comorbidity.
Recording of body weight in primary care is generally opportunistic and dependent on patients attending the practice. We acknowledge that weight measurements in EHRs may be associated with error and bias including measurement error; confounding by indication, if weight changes prompt weight measurements; variation between professionals and family practices in measurement recording;44 and weight-management strategies.28 Higher patient baseline BMI was associated with a higher frequency of BMI measurements recorded over the study period. UK general practices have contractual financial incentives to provide a register of adult patients who have a BMI ≥ 30 kg/m2 measured in the last 15 months121 which may lead to more frequent recording of BMI for obese patients. We reported on the recording of BMI in primary care in a previous study.44 For this study, we selected participants with a minimum of three BMI records. We acknowledge that participants with fewer than three BMI records may show different patterns of weight change and the present results might be biased through their omission. However, we believe that this is one of the largest studies yet reported on body weight changes in the general population. The relatively high levels of comorbidity seen in obese compared with normal weight patients would also likely result in more regular consultations and more frequent recording of BMI. However, it is possible that patients from all BMI categories with three or more BMI measurements recorded over the 9-year study period represent a biased, less healthy sample than the general population. If this is the case then unintentional weight loss, along with comorbidities contributing to weight gain such as mobility impairment, may have influenced BMI changes disproportionately in the current sample.
Conclusions
Findings from this analysis indicate that current non-surgical obesity treatment strategies are failing to achieve sustained weight loss for the majority of obese patients. For patients with a BMI of ≥ 30 kg/m2, maintaining weight loss was rare and the probability of achieving normal weight was extremely low. Research to develop new and more effective approaches to obesity management and prevention are urgently required. Obesity treatment programmes should prioritise prevention of further weight gain, along with the maintenance of weight loss in those who achieve it. However, in the absence of effective interventions targeted at the level of the individual, the greatest opportunity for tackling the current obesity epidemic may be found outside primary care. Research to develop wider-reaching public health policies is needed to prevent obesity at the population level.
