Weight Loss Diet Study: Low Carb vs Low Fat

Not Applicable

Completed

• Conditions: Obesity; Insulin Resistance
• Interventions: Behavioral: Low-Carbohydrate Diet; Behavioral: Low-Fat Diet

• Registration Number: NCT01661426
• Lead Sponsor: Stanford University

Brief Summary

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

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.

Study Timeline

• Study Start: 2012-04
• Study First Submitted: 2012-08-07
• Study First Submitted QC: 2012-08-07
• Study First Posted: 2012-08-09
• Primary Completion: 2013-03
• Study Completion: 2013-03
• Status Verified: 2023-02
• Last Update Submitted: 2023-02-18
• Last Update Posted: 2023-02-22

Recruitment & Eligibility

• Status: COMPLETED
• Sex: All
• Target Recruitment: 61

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

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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)

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Study & Design

• Study Type: INTERVENTIONAL
• Study Design: CROSSOVER

Arm && Interventions

Group	Intervention	Description
Low-Carbohydrate Diet first, then Low-Fat Diet (IR)	Low-Carbohydrate Diet	Participants who were more insulin resistant based on the median AUC for insulin concentrations measured from OGTT prior to randomization.
Low-Carbohydrate Diet first, then Low-Fat Diet (IR)	Low-Fat Diet	Participants who were more insulin resistant based on the median AUC for insulin concentrations measured from OGTT prior to randomization.
Low-Fat Diet first, then Low-Carbohydrate Diet (IS)	Low-Fat Diet	Participants who were more insulin sensitive based on the median AUC for insulin concentrations measured from OGTT prior to randomization.
Low-Fat Diet first, then Low-Carbohydrate Diet (IS)	Low-Carbohydrate Diet	Participants who were more insulin sensitive based on the median AUC for insulin concentrations measured from OGTT prior to randomization.

Primary Outcome Measures

Name	Time	Method
Change in weight	Baseline and 12 months	Weight change was calculated as the 12 month value minus the baseline value

Secondary Outcome Measures

Name	Time	Method
Change in LDL-Cholesterol	Baseline and 12 months	LDL-cholesterol change was calculated as the 12 month value minus the baseline value.
Change in HDL-Cholesterol	Baseline and 12 months	HDL-cholesterol change was calculated as the 12 month value minus the baseline value.
Comparison of plasma fatty acid composition changes in participants on low fat and low carbohydrate diets after 6 months.	Baseline and 6 months
Change in Triglycerides	Baseline and 12 months	Triglycerides change was calculated as the 12 month value minus the baseline value.
Change in systolic and diastolic blood pressure	Baseline and 12 months	Blood pressure change was calculated as the 12 month value minus the baseline value.
Change in Fasting Insulin	Baseline and 12 months	Fasting insulin change was calculated as the 12 month value minus the baseline value
Change in insulin AUC	Baseline and 12 months	Insulin area under the curve (AUC) change was calculated as the 12 month value minus the baseline value.
Plasma fatty acid composition at baseline	Baseline	Comparison of the plasma fatty acid composition between insulin sensitive and resistant participants at baseline.
Change in Fasting Glucose	Baseline and 12 months	Fasting glucose change was calculated as the 12 month value minus the baseline value.
Correlations between insulin markers and plasma fatty acid composition at baseline.	Baseline
Interaction between insulin status and diet on 6-month changes in the plasma fatty acid composition.	6 months
Correlations between changes in insulin markers, dietary components, and plasma fatty acid composition after 6 months.	6 months

Trial Locations

Locations (1)

Stanford University School of Medicine; 🇺🇸 Stanford, California, United States