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© 2002 American Public Health Association
RESEARCH AND PRACTICE |
Julie C. Will, David F. Williamson, and Earl S. Ford are with the National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, Ga. Eugenia E. Calle and Michael J. Thun are with the American Cancer Society, Atlanta, Ga.
Correspondence: Requests for reprints should be sent to Julie C. Will, PhD, Division of Nutrition and Physical Activity, National Center for Chronic Disease Prevention and Health Promotion, 4770 Buford Hwy, NE, Mail Stop K-26, Atlanta, GA 30341-3724 (e-mail: jxw6{at}cdc.gov).
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INTRODUCTION |
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 TOP INTRODUCTION METHODSRESULTSDISCUSSIONReferences |
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Observational studies have established that obesity is associated with a substantially increased risk of developing type 2 diabetes.1 Whether intentional weight loss reduces the risk of obese persons’ developing diabetes remains unclear, however. Two randomized controlled trials for the primary prevention of type 2 diabetes in adults have included lifestyle intervention arms emphasizing modest weight loss.2,3
Relatively few observational studies have examined the association of weight loss with diabetes risk,4 and no published observational study has differentiated the effects of intentional weight loss from those of unintentional weight loss. This is important because unintentional weight loss may be associated with the clinical onset of diabetes.5 This is the first observational study to use data on weight-loss intention in examining the prospective relationship between weight change and the incidence of diabetes in overweight adults.
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METHODS |
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TOPINTRODUCTIONMETHODSRESULTSDISCUSSIONReferences |
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We analyzed data from the first Cancer Prevention Study, a 13-year prospective study of more than 1 million participants conducted by the American Cancer Society.6 In brief, this study used volunteer researchers who administered a baseline questionnaire (October 1959 through March 1960), conducted annual tracing of subjects, administered supplemental questionnaires (1961, 1963, and 1965), and completed a final follow-up questionnaire (October 1972). Death certificates were used to determine the exact cause of death.7 Additional details of the study have been published elsewhere.6,8
From the 453 872 men and 589 811 women older than 30 years with complete baseline questionnaires, we excluded persons with a report of a previous diagnosis of diabetes, those who did not fill out their own baseline questionnaire, and those who were not overweight before baseline (prebaseline body mass index [BMI] < 25 kg/m2).
For each sex, we conducted 2 proportional hazards analyses9 to examine associations between weight change and the incidence of diabetes mellitus during the following 13 years. Weight change was assessed at baseline. First, respondents were asked whether their weight had changed. If they said yes, they were asked whether the change was a gain or loss, about how many pounds the change was, and whether they had tried to bring about this change. No questions about weight or weight change were asked in any of the follow-up questionnaires.
An incident case of diabetes mellitus was determined by a report of diabetes on any of the questionnaires completed after baseline or by a death certificate listing diabetes as an underlying or contributing cause of death. The first analysis estimated diabetes incidence by 5 categories of weight change (no change, unintentional gain, unintentional loss, intentional gain, and intentional loss); the second examined diabetes incidence by 5 categories of intentional weight loss (losses of 0.1–19.9, 20.0–39.9, 40.0–59.9, 60.0–79.9, and 
80 lb [0.1–9.0, 9.1–18.1, 18.2–27.1, 27.2–36.2, and 36.3 kg]).9,10 At minimum, we adjusted all analyses for age and prebaseline BMI. Fully adjusted analyses included a number of other baseline characteristics potentially related to diabetes or weight change (see Table 1
). We excluded anyone who was missing data on the exposure or for any of the covariates. Detailed definitions of covariates can be obtained from the authors.
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RESULTS |
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TOPINTRODUCTIONMETHODSRESULTSDISCUSSIONReferences |
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Overall, the diabetes incidence rate was 598 per 100 000 person-years of follow-up for overweight men and 665 per 100 000 person years of follow-up for women (Table 1
). At baseline, 13 545 (13.3%) of 101 285 men and 23 200 (20.8%) of 111 285 women had lost weight intentionally (Table 1). Men who had lost weight intentionally were protected against development of diabetes, compared with men who had reported that their weight had not changed (incidence density ratio [IDR] = 0.79, 95% confidence interval [CI] = 0.73, 0.86). Women who lost weight intentionally also had a lower rate of diabetes than did the referent group (IDR = 0.72, 95% CI = 0.68, 0.77).
Compared with overweight persons who had not lost weight, those who intentionally lost weight decreased their rate of diabetes as the amount of weight lost increased (Table 2). A test for linear trend proved positive for both men (P = .0156) and women (P = .0001). On average, for every 20 lb lost, men decreased their rate of diabetes by 11%; women decreased it by 17%.
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DISCUSSION |
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TOPINTRODUCTIONMETHODSRESULTSDISCUSSIONReferences |
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We found that during a 13-year period, overweight men and women who reported intentional weight loss at baseline had a reduction in the rate of developing diabetes of about 25% compared with their counterparts who did not report intentional weight loss. The rate of diabetes decreased linearly with increasing amount of weight lost.
Our findings are supported by experiments showing that glycemic levels in obese persons improve after weight loss.11 In addition, several epidemiological studies have reported that general weight loss (intent unknown) was associated with decreased incidence of diabetes.1,12 However, at least 2 previous studies disagree with our findings.13,14
That studies disagree may be related to differences in study design. For example, our study was limited in several ways that may have influenced our findings. First, we used self-reported diabetes along with death certificates to uncover cases of diabetes. We suspect that fewer than half of respondents with diabetes knew they had it.15 Therefore, diabetes would be underreported in our study. This would not be expected to bias our results, however, unless weight change or weight change intention influences awareness of true diabetes status. If those who lost weight intentionally were diagnosed with diabetes at higher rates than those whose weight had not changed, the resulting bias (away from the null value) would lead us to report a stronger negative association between intentional weight loss and diabetes than actually exists. The bias would be toward the null value if the converse were true.
Second, weight loss was measured at only one point in time around baseline, and it is unclear whether this weight loss was sustained. Although studies of weight loss in the clinical setting indicate that weight loss is very difficult to maintain, one population-based study16 found that half of persons who lost weight intentionally maintained that weight loss for at least 1 year, and 25% maintained the loss for at least 5 years. Some researchers suggest that even short-term weight loss may have longer-term benefits through restoration of B-cell capacity.17 Third, our results might be different if we could completely control for residual confounding.
In conclusion, we found that intentional weight loss was associated with a reduction in the rate of developing diabetes. Ongoing analyses of randomized clinical trials can help determine whether intentional weight loss itself decreases the incidence of diabetes in overweight persons.
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Footnotes |
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J. C. Will helped plan the analysis of data, analyzed the data, and wrote a substantial portion of the article. D. F. Williamson helped plan the analysis of data, reviewed results, and assisted in the writing of the article. E. S. Ford contributed to the interpretation of results and the writing of the article. E. E. Calle and M. J. Thun provided the first Cancer Prevention Study cohort data, contributed to the study design, and assisted in the writing of the article.
Human Participant Protection
No IRB approval was required for this study.
Accepted for publication August 28, 2001.
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References |
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TOPINTRODUCTIONMETHODSRESULTSDISCUSSIONReferences |
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1. Ford ES, Williamson DF, Liu S. Weight change and diabetes incidence: findings from a national cohort. Am J Epidemiol. 1997;146:214–222.
2. Eriksson J, Lindstrom J, Valle T, et al. Prevention of type II diabetes in subjects with impaired glucose tolerance: the Diabetes Prevention Study (DPS) in Finland. Study design and 1-year interim report on the feasibility of the lifestyle intervention programme. Diabetologia. 1999;42:793–801.[Medline]
3. The Diabetes Prevention Program Research Group. The Diabetes Prevention Program. Design and methods for a clinical trial in the prevention of type 2 diabetes. Diabetes Care. 1999;22:623–634.[Abstract]
4. Wannamethee SG, Shaper GA. Weight change and duration of overweight and obesity in the incidence of type 2 diabetes. Diabetes Care. 1999;22:1266–1272.[Abstract]
5. Maggio CA, Pi-Sunyer FX. The prevention and treatment of obesity: application to type 2 diabetes. Diabetes Care. 1997;20:1744–1766.[Medline]
6. Garfinkel L. Selection, follow-up, and analysis in the American Cancer Society prospective studies. Natl Cancer Inst Monogr. 1985;67:49–52.
7. International Classification of Diseases. 7th ed. Geneva, Switzerland: World Health Organization; 1955.
8. Hammond EC. Smoking in relation to the death rates of one million men and women. Natl Cancer Inst Monogr. 1966;19:127–204.
9. SAS/STAT User’s Guide. Version 64. Vol 2. Cary, NC: SAS Institute Inc; 1989.
10. Cox DR. Regression and life tables. J R Stat Soc B. 1972;34:187–220.
11. Goldstein DJ. Beneficial health effects of modest weight loss. Int J Obes. 1992;16:397–415.[Medline]
12. Colditz GA, Willett WC, Rotnitzky A, Manson JE. Weight gain as a risk factor for clinical diabetes mellitus in women. Ann Intern Med. 1995;122:481–486.
13. Modan M, Karasik A, Halkin H, et al. Effect of past and concurrent body mass index on prevalence of glucose intolerance and type 2 (non-insulin-dependent) diabetes and on insulin response: the Israel study of glucose intolerance, obesity and hypertension. Diabetologia. 1986;29:82–89.[Medline]
14. French SA, Folsom AR, Jeffery RW, Zheng W, Mink PJ, Baxter JE. Weight variability and incident disease in older women: the Iowa Women’s Health Study. Int J Obes. 1997;21:217–223.
15. Harris MI, Hadden WC, Knowler WC, Bennett PH. Prevalence of diabetes and impaired glucose tolerance and plasma glucose levels in US population aged 20–74 yr. Diabetes. 1987;36:523–534.[Abstract]
16. McGuire MT, Wing, RR, Hill JO. The prevalence of weight loss maintenance among American adults. Int J Obes. 1999;23:1314–1319.
17. Wing RR, Marcus MD, Salata R, Epstein LH, Miaskiewicz S, Blair EH. Effects of a very-low-calorie diet on long-term glycemic control in obese type 2 diabetic subjects. Arch Intern Med. 1991;151:1334–1340.
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