Weight Loss Diet Study: Low Carb vs Low Fat

Study Results

Results pending

The study team has not published outcome measurements, participant flow, or safety data for this trial yet. Check back later for updates.

Basic Information

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Recruitment Status

COMPLETED

Clinical Phase

NA

Total Enrollment

61 participants

Study Classification

INTERVENTIONAL

Study Start Date

2012-04-30

Study Completion Date

2013-03-31

Brief Summary

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The traditional weight loss diet recommended by health professionals has been a low-fat, high-carbohydrate, calorie restricted diet. This recommendation has been challenged by a number of alternative dietary strategies, particularly low-carbohydrate diets. In several recent weight loss studies insulin resistant adults had more success with low- vs. high-carbohydrate diets, in contrast to insulin sensitive adults who had either more success or comparable success with the low-fat diets. The investigators enrolled 61 people with a wide range of insulin sensitivity/resistance. After determining their insulin resistance status, the investigators will split them in the middle and randomly assign them to one of four groups for six months: (1) Low-Carbohydrate/Insulin Resistant (LC/IR); (2) Low-Carbohydrate/Insulin Sensitive (LC/IS); (3) Low-Fat/Insulin Resistant (LF/IR); and (4) Low-Fat/Insulin Sensitive (LF/IS) (15 people/group). After 6 months the participants will switch diet for the following 6 months, i.e. those randomized to the Low-Carbohydrate diet will switch to the Low-Fat diet and vice-versa. The primary outcome of this study is to determine whether weight loss success can be increased if one follows the dietary approach appropriately matched to their insulin resistance status. Secondary outcomes include fasting insulin, glucose, lipids, and fatty acid composition.

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Detailed Description

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The investigators hope to learn whether matching the weight loss diet to one's insulin resistance status will increase weight loss the success. The relevance of these findings is highlighted by the fact that the national recommendations for weight loss are to follow a high-carbohydrate, low-fat diet. This would imply that about half the population has been given the wrong advice in regards to the most successful dietary pattern for weight loss.

Plasma fatty acid composition patterns have been shown to be associated with both insulin resistance and/or carbohydrate intake. As secondary analyses, the investigators will explore: (1) differences in plasma fatty acid composition between insulin sensitive and resistant participants at baseline; (2) the correlations between insulin markers and plasma fatty acid composition at baseline; (3) the interaction between insulin status and diet on 6-month changes in the plasma fatty acid composition; (4) plasma fatty acid composition changes in participants on low fat and low carbohydrate diets after 6 months; and (5) the correlations between changes in insulin markers, dietary components, and plasma fatty acid composition after 6 months.

Conditions

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Obesity Insulin Resistance

Study Design

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Allocation Method

RANDOMIZED

Intervention Model

CROSSOVER

The study employed a 2 x 2 crossover design: LF vs. LC diets and more IR vs. more IS. Study participants were classified as more IR or more IS based on the median AUC for insulin concentrations measured from an oral glucose tolerance test (OGTT) prior to randomization. Participants above the median were considered more IR and those below the median were considered more IS. A random number generator was used to stratify the randomization to LF vs. LC by insulin resistance status and gender. Participants followed their assigned diet for 6 months and then switched to the opposite diet for another 6 months.

Primary Study Purpose

PREVENTION

Blinding Strategy

QUADRUPLE

Participants Caregivers Investigators Outcome Assessors

Study Groups

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Low-Carbohydrate Diet first, then Low-Fat Diet (IR)

Participants who were more insulin resistant based on the median AUC for insulin concentrations measured from OGTT prior to randomization.

Group Type ACTIVE_COMPARATOR

Low-Carbohydrate Diet

Intervention Type BEHAVIORAL

Counseling/instruction on how to follow a healthy low-carbohydrate diet for 6 months. One evening class/week for 8 weeks (8 total classes). Then one class every other week for 8 weeks (4 total classes). Then one class every four weeks for 8 weeks (2 total classes): 14 evening classes, total.

Low-Fat Diet

Intervention Type BEHAVIORAL

Counseling/instruction on how to follow a healthy low-fat diet for 6 months. One evening class/week for 8 weeks (8 total classes). Then one class every other week for 8 weeks (4 total classes). Then one class every four weeks for 8 weeks (2 total classes): 14 evening classes, total.

Low-Fat Diet first, then Low-Carbohydrate Diet (IS)

Participants who were more insulin sensitive based on the median AUC for insulin concentrations measured from OGTT prior to randomization.

Group Type ACTIVE_COMPARATOR

Low-Carbohydrate Diet

Intervention Type BEHAVIORAL

Counseling/instruction on how to follow a healthy low-carbohydrate diet for 6 months. One evening class/week for 8 weeks (8 total classes). Then one class every other week for 8 weeks (4 total classes). Then one class every four weeks for 8 weeks (2 total classes): 14 evening classes, total.

Low-Fat Diet

Intervention Type BEHAVIORAL

Counseling/instruction on how to follow a healthy low-fat diet for 6 months. One evening class/week for 8 weeks (8 total classes). Then one class every other week for 8 weeks (4 total classes). Then one class every four weeks for 8 weeks (2 total classes): 14 evening classes, total.

Interventions

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Low-Carbohydrate Diet

Counseling/instruction on how to follow a healthy low-carbohydrate diet for 6 months. One evening class/week for 8 weeks (8 total classes). Then one class every other week for 8 weeks (4 total classes). Then one class every four weeks for 8 weeks (2 total classes): 14 evening classes, total.

Intervention Type BEHAVIORAL

Low-Fat Diet

Counseling/instruction on how to follow a healthy low-fat diet for 6 months. One evening class/week for 8 weeks (8 total classes). Then one class every other week for 8 weeks (4 total classes). Then one class every four weeks for 8 weeks (2 total classes): 14 evening classes, total.

Intervention Type BEHAVIORAL

Eligibility Criteria

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Inclusion Criteria

* Age: \> or = 18 years of age
* Women: Pre-menopausal (self-report) and \<50 years of age
* Men: \<50 years of age
* Race/Ethnicity: All
* BMI (body mass index): 28-40 kg/m2 (need to lose \>10% body weight to achieve healthy BMI)
* Body weight stable for the last two months, and not actively on a weight loss plan
* No plans to move from the area over the next 14 months
* Available and able to participate in the evaluations and intervention for the study period
* Willing to accept random assignment
* To enhance study generalizability, people on medications not noted below as specific exclusions can participate if they have been stable on such medications for at least three months
* Ability and willingness to give written informed consent
* No known active psychiatric illness

Exclusion Criteria

* Pregnant, lactating, within 6 months post-partum, or planning to become pregnant in the next 12 months; no menstruation for the previous 12 months
* Diabetes (type 1 and 2) or history of gestational diabetes or on hypoglycemic medications for any other indication
* Prevalent diseases: Malabsorption, renal or liver disease, active neoplasms, recent myocardial infarction, hypertension (except for those stable on hypertensive medications) (\<6 months) (patient self-report and, if available, review of labs from primary care provider)
* Smokers (because of effect on weight and lipids)
* History of serious arrhythmias, or cerebrovascular disease
* Uncontrolled hyper- or hypothyroidism (TSH not within normal limits)
* Medications: Lipid lowering, diabetes medications, and those known to affect weight/energy expenditure
* Excessive alcohol intake (self-reported, \>3 drinks/day)

Minimum Eligible Age

18 Years

Maximum Eligible Age

50 Years

Eligible Sex

ALL

Accepts Healthy Volunteers

Yes