title: Effects of diet composition on weight loss, metabolic factors and biomarkers in a 1-year weight loss intervention in obese women examined by baseline insulin resistance status.
abstract: BACKGROUND
  Obesity is a risk factor for postmenopausal breast cancer incidence and premenopausal and postmenopausal breast cancer mortality, which may be explained by several metabolic and hormonal factors (sex hormones, insulin resistance, and inflammation) that are biologically related. Differential effects of dietary composition on weight loss and these metabolic factors may occur in insulin-sensitive vs. insulin-resistant obese women.
  
  
  OBJECTIVE
  To examine the effect of diet composition on weight loss and metabolic, hormonal and inflammatory factors in overweight/obese women stratified by insulin resistance status in a 1-year weight loss intervention.
  
  
  RESULTS
  Nondiabetic women who were overweight/obese (n=245) were randomly assigned to a lower fat (20% energy), higher carbohydrate (65% energy) diet; a lower carbohydrate (45% energy), higher fat (35% energy) diet; or a walnut-rich (18% energy), higher fat (35% energy), lower carbohydrate (45% energy) diet. All groups lost weight at follow-up (P<0.0001), with mean (SEM) percent loss of 9.2(1.1)% in lower fat, 6.5(0.9)% in lower carbohydrate, and 8.2(1.0)% in walnut-rich groups at 12months. The diet×time×insulin resistance status interaction was not statistically significant in the model for overall weight loss, although insulin sensitive women at 12months lost more weight in the lower fat vs. lower carbohydrate group (7.5kg vs. 4.3kg, P=0.06), and in the walnut-rich vs. lower carbohydrate group (8.1kg vs. 4.3kg, P=0.04). Sex hormone binding globulin increased within each group except in the lower carbohydrate group at 12months (P<0.01). C-reactive protein and interleukin-6 decreased at follow-up in all groups (P<0.01).
  
  
  CONCLUSIONS
  Findings provide some support for differential effects of diet composition on weight loss depending on insulin resistance status. Prescribing walnuts is associated with weight loss comparable to a standard lower fat diet in a behavioral weight loss intervention. Weight loss itself may be the most critical factor for reducing the chronic inflammation associated with increased breast cancer risk and progression.
authors.affiliation: Department of Family Medicine and Public Health, School of Medicine, University of California, San Diego, La Jolla, CA, USA. Electronic address: clrock@ucsd.edu.
authors.forename: Cheryl L
authors.initials: CL
authors.lastname: Rock
authors.affiliation: Department of Family Medicine and Public Health, School of Medicine, University of California, San Diego, La Jolla, CA, USA.
authors.forename: Shirley W
authors.initials: SW
authors.lastname: Flatt
authors.affiliation: Department of Family Medicine and Public Health, School of Medicine, University of California, San Diego, La Jolla, CA, USA.
authors.forename: Bilge
authors.initials: B
authors.lastname: Pakiz
authors.affiliation: Department of Family Medicine and Public Health, School of Medicine, University of California, San Diego, La Jolla, CA, USA.
authors.forename: Elizabeth L
authors.initials: EL
authors.lastname: Quintana
authors.affiliation: Department of Family Medicine and Public Health, School of Medicine, University of California, San Diego, La Jolla, CA, USA.
authors.forename: Dennis D
authors.initials: DD
authors.lastname: Heath
authors.affiliation: Department of Psychiatry, School of Medicine, University of California, San Diego, La Jolla, CA, USA.
authors.forename: Brinda K
authors.initials: BK
authors.lastname: Rana
authors.affiliation: Department of Family Medicine and Public Health, School of Medicine, University of California, San Diego, La Jolla, CA, USA.
authors.forename: Loki
authors.initials: L
authors.lastname: Natarajan
mesh_terms: D015415:Biomarkers / Q000097:blood; D002097:C-Reactive Protein / Q000378:metabolism; D004038:Diet, Reducing; D004040:Dietary Carbohydrates; D004041:Dietary Fats; D005500:Follow-Up Studies; D006728:Hormones / Q000097:blood; D018836:Inflammation Mediators / Q000097:blood; D007333:Insulin Resistance; D015850:Interleukin-6 / Q000097:blood; D031324:Juglans; D009765:Obesity / Q000178:diet therapy*; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism; D015431:Weight Loss
chemical_list: D015415:Biomarkers; D004040:Dietary Carbohydrates; D004041:Dietary Fats; D006728:Hormones; C508600:IL6 protein, human; D018836:Inflammation Mediators; D015850:Interleukin-6; D012738:Sex Hormone-Binding Globulin; D002097:C-Reactive Protein
keywords: Breast cancer; Diet composition; Insulin resistance; Walnuts; Weight loss