Carbohydrate: Amount and Type Affecting Risk for CVD and Diabetes

描述(由申请人提供)： 预防心血管疾病(CVD)和糖尿病的最佳饮食尚不确定。减少饱和脂肪和反不饱和脂肪可降低心血管风险。然而，在低饱和和超不饱和脂肪的背景下，饮食在其他提供能量的营养物质上可能有很大的不同，特别是碳水化合物。一些权威人士主张减少碳水化合物，代之以脂肪和蛋白质。据推测，这样的饮食变化将改善血脂、胰岛素抵抗和血压。也有人认为，缓慢吸收的碳水化合物，即那些血糖指数较低的碳水化合物，对这些心血管疾病和糖尿病的风险因素有有益的影响。支持性证据来自小规模研究，总体而言，这些研究不足以指导营养政策。我们建议进行一项大规模的受控饮食试验，研究碳水化合物从高水平(58%千卡)降至低水平(43%千卡)和将血糖指数从高水平(85)降至低水平(55)对与饮食相关的主要心血管危险因素以及与2型糖尿病密切相关的胰岛素敏感性的影响。试验参与者(n=160，大约50%是女性，50%是非洲裔美国人)将有高血压和其他心血管疾病危险因素的高患病率，如血脂异常和超重或肥胖。核心设计是一项随机对照喂养研究，使用与DASH和OmniHeart试验相同的方法。四种饮食都将进行为期5周的测试：高碳水化合物或低碳水化合物，每种都有较高或较低的血糖指数。参赛者将保持体重稳定状态。主要终点将是收缩压；血浆低密度脂蛋白胆固醇、高密度脂蛋白胆固醇和甘油三酯；以及通过静脉葡萄糖耐量试验直接确定的胰岛素敏感性。次要终点将包括舒张压；与代谢综合征的血脂异常有关的致动脉粥样硬化脂蛋白颗粒类型；果糖胺；以及通过标准风险方程估计的总体心血管风险。主要饮食对比将是高碳水化合物、高血糖指数与低碳水化合物、低血糖指数。其他对比将旨在扩大碳水化合物水平和血糖指数；即每个碳水化合物水平较高和较低血糖指数的影响，以及高碳水化合物水平和低碳水化合物水平对每个血糖指数的影响。这类“喂养研究”的目的是确定饮食碳水化合物水平和类型对心血管疾病和胰岛素抵抗风险的生物学影响。我们预计，结果将立即适用于公共卫生和临床指南，并将影响营养政策。

DESCRIPTION (provided by applicant): The optimal diet to prevent cardiovascular disease (CVD) and diabetes is uncertain. Reducing saturated fat and transunsaturated fat lowers cardiovascular risk. However, within the context of low saturated and transunsaturated fat, diets can vary widely in other energy-providing nutrients, particularly carbohydrate. Some authorities advocate reducing carbohydrate and replacing it with fat and protein. It is hypothesized that such dietary changes will improve blood lipids, insulin resistance, and blood pressure. It has also been argued that slowly absorbed carbohydrates, i.e. those with a low glycemic index, have beneficial effects on these risk factors for CVD and diabetes. Supportive evidence comes from small scale studies, which in aggregate have been insufficient to guide nutrition policy. We propose to conduct a large-scale, controlled dietary trial that examines the effects of reducing carbohydrate from a high level (58% kcal) to a low level (43% kcal) and of lowering glycemic index from a high level (>85) to a low level (<55) on the major established diet-related CVD risk factors as well as insulin sensitivity, strongly linked to type 2 diabetes. Trial participants (n=160, approximately 50% women, 50% African-American) will have elevated blood pressure and a high prevalence of other CVD risk factors such as dyslipidemia and overweight or obesity. The core design is a randomized controlled feeding study that uses the same methodology as the DASH and OmniHeart trials. Four diets will be tested for 5 weeks each: higher or lower carbohydrate, each with higher or lower glycemic index. The participants will be maintained in the weight-stable state. The primary endpoints will be systolic blood pressure; plasma LDL cholesterol, HDL cholesterol and triglycerides; and insulin sensitivity determined directly by intravenous glucose tolerance test. Secondary endpoints will include diastolic blood pressure; atherogenic lipoprotein particle types related to dyslipidemia of the metabolic syndrome; fructosamine; and overall CVD risk estimated by standard risk equations. The primary diet contrast will be high carbohydrate, high glycemic index vs low carbohydrate, low glycemic index. Other contrasts will aim to distentagle level of carbohydrate and glycemic index; i.e. the effects of higher vs lower glycemic index at each carbohydrate level, and the effects of high vs low carbohydrate level at each glycemic index. The objective of this type of "feeding study" is to establish definitively the biological effects of dietary carbohydrate level and type on risk of CVD as well as insulin resistance. We expect that the results will be immediately applicable to public health and clinical guidelines, and will influence nutrition policy.