Obesity is a national epidemic with multiple causes and complex solutions. Research in both animals and humans has suggested that the inclusion of dairy foods into a moderate calorie restricted diet can increase weight loss and fat loss. Our proposed project extends these prior findings by determining, for the first time, how inclusion of dairy in a calorie-restricted diet changes the amount of visceral adiposity in overweight and obese subjects. The investigators also propose unique studies to evaluate the potential mechanism(s) by which dairy promotes weight and fat loss during dieting, through an examination of adipocyte size, gene expression, and inflammatory markers. The hypotheses under investigation are (1) that inclusion of dairy foods in a modest energy restricted diet will significantly increase body fat loss compared to a control diet; (2) that dairy products in a modest energy restricted diet will result in greater fat loss from intra-abdominal adipose tissue compared to the control, 3) components of dairy products up- or down-regulate the secretion of metabolically-relevant hormones during the postprandial and inter-meal periods, 4) dairy products will promote satiety and/or satiation, 5) dairy foods reduce adipocyte differentiation and/or enhance adipocyte apoptosis, leading to concomitant white adipose tissue (WAT) expression changes for genes playing a role in these processes, 6) dairy foods will reduce adipocyte lipid storage and enhance pathways associated with thermogenesis and mitochondrial function in WAT, as reflected in gene expression changes and reduced adipocyte size, and 7) dairy foods included in a modest energy restricted diet will decrease inflammation in WAT and other tissues, thus decreasing circulating cytokines, increasing zinc status, decreasing expression of inflammatory markers in WAT, and reducing WAT macrophage infiltration.
84 overweight and overweight and obese adult males and females will be recruited from the faculty, staff, and student populations at University of California-Davis as well as the greater Davis and Sacramento communities. Each intervention arm will require 42 adults; 35 for statistical power on weight loss + 14 more for attrition during the weight loss intervention. Statistical power for fat loss requires only 20 subjects/treatment arm. Subjects will be enrolled in 7 cohorts of 12 each and will be randomly assigned to either control or dairy diets. Subjects will meet the following additional inclusion and exclusion criteria:
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
78
12 week energy restriction with 3-4 servings of dairy foods/day.
less than 1 serving of dairy foods per day.
Western Human Nutrition Research Center
Davis, California, United States
Change in body weight
Weight measured in kg
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in body fat
Total body fat assessed using dual energy X-ray absorptiometry (DXA)
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in intra-abdominal adipose tissue (IAAT)
Intra-abdominal adipose tissue IAAT volume measured in cubic centimeters using computed tomography (CT) transabdominal slices
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in subcutaneous adipose cell number and size
Subcutaneous adipose tissue samples obtained by needle biopsy prepared for histological examination of cell number and size in square micrometers (uM2)
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in subcutaneous adipose tissue inflammation
Subcutaneous adipose tissue samples obtained by needle biopsy were prepared for histological examination of the number of macrophages.
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in subcutaneous adipose tissue gene expression
Subcutaneous adipose tissue samples obtained by needle biopsy were prepared for RNA extraction
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in insulin
Serum insulin concentration (pmol/L) measured using multiplex technology.
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in glucose
Plasma glucose concentration (mmol/L) measured using standard clinical methods
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in total cholesterol
Serum cholesterol concentration (mmol/L) measured using standard clinical methods
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in low density lipoprotein (LDL) cholesterol
Serum LDL cholesterol concentration (mmol/L) measured using standard clinical methods
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in high density lipoprotein (HDL) cholesterol
Serum HDL cholesterol concentration (mmol/L) measured using standard clinical methods
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in vitamin D (calciferol) metabolites
Serum 25-OH Vitamin D (nmol/L) and 1,25 (OH)2 vitamin D concentration (pmol/L) measured using radioimmunoassay (RIA)
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in leptin
Serum leptin concentration (ng/ml) measured using multiplex technology.
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in adiponectin
Serum adiponectin concentration (ug/mL) measured using multiplex technology.
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in inflammatory cytokines
Serum inflammatory cytokine concentration (pg/mL) measured using multiplex technology.
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in high sensitivity C-reactive protein (hs-CRP)
Serum hs-CRP concentration (mg/L) measured using immunoassay
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in amylin
Serum amylin concentration measured using multiplex technology.
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in peptide-YY (PYY)
Serum PYY concentration measured using multiplex technology.
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in cholecystokinin (CCK)
Serum CCK concentration measured using radioimmunoassay
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in glucagon like peptide-1 (GLP-1)
Serum GLP-1 concentration measured using multiplex technology.
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in gastric inhibitory peptide (GIP)
Serum GIP concentration measured using multiplex technology.
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in sun exposure
Sun exposure was estimated from a personal diary kept weekly for recording time outdoors in hourly increments from 7 am to 7 pm combined with a clothing and sunscreen use standard key. Ultraviolet B (UVB) data was collected from various regional climate stations enrolled in the USDA UVB Monitoring Research Program (UVMRP).
Time frame: measured twice per week for 12 consecutive weeks of study diet
Change in skin reflectance
Spectrophotometric measure of skin pigmentation for assessment of vitamin D status
Time frame: measured at end of run-in diet and after 12 weeks of study diet
Change in salivary cortisol in response to a meal
Cortisol concentration measure by high sensitivity enzyme linked immunoassay (nmol/L)
Time frame: 15 minutes before, and 30, 45 and 60 min after lunch
Change in salivary cortisol in response to a buffet
Cortisol concentration measure by high sensitivity enzyme linked immunoassay (nmol/L)
Time frame: before and 30 min after buffet
Change in salivary cortisol in response to weight loss
Cortisol concentration measure by high sensitivity enzyme linked immunoassay (nmol/L)
Time frame: measured at end of run-in diet and after 12 weeks of study diet
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