This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Epidemiological and observational studies indicate that a vegetarian diet should have beneficial effects on cardiovascular risk factors, but there have been no systematic studies of such a diet. In order to better understand the metabolic and physiologic effects of a vegetarian diet in healthy subjects, and to determine the motivations and barriers to complying with such a diet, we propose to do a study with three specific aims to test three hypotheses:
Aim 1. To perform a randomized order, crossover study on healthy subjects. Hypothesis 1. There will be subject compliance to and retention in an LOV diet from previously omnivore subjects with minimal gastrointestinal side effects, provided that they receive palatable, weight maintaining diets, for the length of the study. Each subject will spend eight weeks on a lactoovovegetarian (LOV) diet and eight weeks on an omnivore diet, with a four-week washout between diets. The diets will have the same percent composition of protein, fat and carbohydrate. We hypothesize that previously omnivore subjects will be able to adjust to an LOV diet with minimal gastrointestinal side effects, that we can provide them with palatable, weight maintaining diets, and that the subjects will stay on the diets for the length of time required of the study. The outcome variable measured will be maintenance of a stable weight.
Aim 2. To measure several physiologic, metabolic, and nutritional parameters on the subjects. Hypothesis 2. Subjects on the LOV diet will have lower systolic and diastolic blood pressure, lower fasting glucose and insulin levels, lower levels of proinflammatory and prothrombotic markers, and improved lipid profiles, compared to their values on the omnivore diet. During each 8-week block, subjects will have twice weekly measurements of weight, and systolic and diastolic blood pressures. At 4 weeks and 8 weeks, they will have measurements of resting energy expenditure (REE), general laboratory values, lipid profiles, hormonal levels, nutritional indices, proinflammatory and prothromobotic markers, and 24-hour urine chemistries. They will have DEXA scans of body composition at initial screening and after each diet period. We hypothesize that on the LOV diet, subjects will have lower systolic and diastolic blood pressures, lower fasting glucose and insulin resistance, lower levels of proinflammatory and prothrombotic markers, and lower total cholesterol, LDL, and triglyceride levels, compared to their values on the omnivore diet. They will have decreased 24-hour urinary excretion of calcium, and hence improved calcium balance. The outcome variables will be the values of these parameters on the two diets.
Aim 3. To develop a recruitment and retention instrument by assessing subjects' motivation for participating in and satisfaction with the conduct of the study and monitoring their difficulty in compliance with the vegetarian diet. Hypothesis 3. Based upon our survey instrument and in-person interviews, highly motivated and satisfied subjects will have a higher likelihood of being recruited and retained in the study. Both quantitative and qualitative approaches will be used in this study. We will see whether the intensive monitoring and direct feedback provided by this study during the LOV diet increases subject compliance with the diet. We will also see whether the change in diet is accurately documented in three forms of dietary assessment: daily food diaries, 24-hour recall, and semi-quantitative food frequency questionnaires. These assessments will be compared to the known composition of the diets actually provided to the subjects. The main outcome variables will be subjects' subjective responses to being a study participant, and their awareness of the change in their diets, as reflected in the three dietary assessment methods. If these three hypotheses should be verified in healthy subjects, these studies will be extended to older men and women with hypertension, diabetes, or the metabolic syndrome, who might be expected to benefit even more from the LOV diet. A vegetarian diet may prove to be a highly effective intervention to help reduce cardiovascular risk factors in humans.
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