Weight Loss Diet Study: Low Carb vs Low Fat
Condition: Obesity; Insulin Resistance
MeSH terms: Insulin Resistance; Weight Loss
Study type: Interventional

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.
    

Intervention name(s): Low-Carbohydrate Diet; Low-Fat Diet
Intervention type(s): Behavioral; Behavioral
Intervention description(s): 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.; 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.
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: 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.
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Primary purpose: Prevention
Keywords: Adults; Weight loss; Diet; Insulin Resistance; Fatty acid composition