Factors which predict variance in weight change

为了调查能量消耗如何随喂养过多和喂养不足而变化，正在进行以下研究。在一项研究中，在仔细校准了体重维持EE后，个体在呼吸室中进行了一系列24小时EE的测量，在呼吸室中，他们禁食或过量喂养(体重维持需要的200%)一系列在常量营养素含量上不同的饮食。这是为了进一步研究低蛋白饮食或高蛋白饮食是否可以改善适应性产热作用招募的检测。此外，还进行了行为、代谢和激素测试，以检查相关特征，并探讨EE变化的机制。这些人还将接受长期跟踪，看看哪些因素可以预测体重变化。来自前19个完成这项研究的人的结果发现，能量消耗随着禁食和过度进食的变化是可以重现的。此外，在那些以正常蛋白质、高脂肪或高碳水化合物饮食过量的人中，过度喂养导致的能量消耗增加最多。低蛋白质日粮的能量消耗没有显著增加。根据禁食和过量进食时能量消耗的差异，可以计算出食物的热效应(TEF)。我们发现TEF与肥胖成反比。因此，TEF可能是体重增加的诱因，也可能是对体重增加的一种适应。由于肥胖症的增加可能会隔绝可能增加TEF的腹部热量损失，我们正在研究中央隔热对与过度喂养相关的EE和TEF变化的影响。我们还在继续测量过量进食和禁食的EE，并调查这些变化是否预示着长期的体重增加。 由于最近在人类中发现了棕色脂肪的存在及其在产热中的可能作用，我们用标记的葡萄糖进行了正电子发射扫描。由于棕色脂肪会被低温激活，我们已经确定，在16摄氏度下暴露2小时后，我们可以看到棕色脂肪。然后，我们目前调查了冷暴露后可见棕色脂肪的个体是否在过量进食后可见棕色脂肪。在寒冷暴露后出现可见的棕色脂肪之后，在我们的代谢室中，使用高脂肪正常蛋白质饮食的个体被过量喂养了他们能量需求的200%。第二天早上，他们接受了PET-CT扫描；一些人在早餐前(在他们最后一顿暴食后大约12小时)和一些人在类似的暴食早餐之后(大约在他们最后一餐后4小时)进行了这项扫描。我们没有发现在高脂肪过量喂养后过度喂养时棕色脂肪被激活的证据，这表明棕色脂肪并不调节与过度喂养相关的能量消耗增加。我们正计划研究在高碳水化合物过量喂养24小时后，棕色脂肪是否可能被激活。 在一项相关的研究中，在测量了过度和喂养不足的EE之后，还在接受了一系列新陈代谢和行为测试(包括肌肉和脂肪的活组织检查)后，患者接受了为期6周的住院饮食方案，涉及喂养不足(对于超重和肥胖的人)或过度喂养(对于瘦的、肥胖抵抗的人)。在住院研究期间，仔细测量了食物摄入量、能量消耗和能量损失的所有方面，以确定体重增加或减少的差异是否可归因于适应性产热作用或其他因素的招募。我们目前已经完成了12个人的减肥研究。我们没有发现最初的能量消耗变化与过度进食和禁食与减肥之间的任何联系。然而，我们已经能够计算出每个人的卡路里平衡(摄入的卡路里与排泄的卡路里的量)，并将它们与总体体重减轻进行比较。即使考虑到减肥过程中能量消耗和体力活动的变化，我们也发现，在一些人身上，体重减轻与我们可以测量的卡路里数量之间存在很大差异；也就是说，根据卡路里赤字，一些人减掉的体重比预期的要多。我们正在调查可能解释这种差异的因素。。 这两项研究的招募工作正在进行中。

In order to investigate how energy expenditure changes with over and underfeeding the following studies are underway. In one study, after careful calibration of weight maintenance EE, individuals undergo a series of measurements of 24 hour EE in a respiratory chamber in which they are fasting or overfed (by 200% of weight maintenance needs) a series of diets that vary in macronutrient content. This is to further investigate whether low or high protein diets may improve the detection of recruitment of adaptive thermogenesis. In addition, behavioral, metabolic and hormonal tests are performed to examine associated characteristics and to investigate the mechanism of the changes in EE. These individuals will also be followed up long term to look at what factors predict weigh change. Results from the first 19 individuals to complete this study have found that the change in energy expenditure with fasting and with overfeeding is reproducible. In addition, the increase in energy expenditure with overfeeding was highest in those overfed a normal protein high fat or high carbohydrate diet. Energy expenditure did not increase significantly with low protein diets. Based on the difference in energy expenditure measured during fasting and overfeeding, the thermic effect of food (TEF) can be calculated. We have found that TEF is inversely associated with adiposity. Thus TEF may predispose to weight gain or be an adaptation to increased bodyweight. As increased adiposity may insulate against trans-abdominal heat loss which may increase TEF, we are investigating the effect of central insulation on the EE and TEF changes associated with overfeeding. We are also continuing to measure EE with overfeeding and fasting, and investigating whether these changes predict longer term weight gain. Because of the recent discovery of the presence of brown fat in humans and its possible role in thermogenesis, we performed positron emission scans with labeled glucose. As brown fat is activated by cold temperatures, we have established that we can visualize brown fat after 2 hours of exposure to 16 degrees Celsius. We then currently investigated whether individuals with visualized brown fat after cold exposure, have visualized brown fat after overfeeding. Following demonstration of visible brown fat after cold exposure individuals were overfed by 200% of their energy needs using a high fat normal protein diet while in our metabolic chamber. The next morning they underwent a PET-CTscan; this was performed in some individuals prior to breakfast (approximately 12 hours after their last overfeeding meals) and in some individuals following a similar overfeeding breakfast (approximately 4 hours after their last meal). We found no evidence of activation of brown fat with overfeeding following a high fat overfeeding, indicating that brown fat does not mediate the increased energy expenditure associated with overfeeding. We are planning to investigate whether brown fat might be activated following 24 hours of high carbohydrate overfeeding. In a related study, after measurement of EE with over and underfeeding, and also after undergoing a series of metabolic and behavioral testing (including biopsies of muscle and fat), individuals areadmitted for 6 weeks of an inpatient dietary protocol involving underfeeding (for overweight and obese individuals) or overfeeding (for lean, obesity resistant individuals). During the inpatient study, all aspects of food intake, energy expenditure, and energy loss are carefully measured to determine if differences in weight gain or loss can be attributed to recruitment of adaptive thermogenesis or other factors. We have currently completed 12 individuals who have undergone the weight loss study.We have not found any association between the initial energy expenditure changes with overfeeding and fasting and weight loss. However, we have been able to calculate the calorie balance in each individual (the amount of calories fed versus those excreted) and compared them to overall weight loss. Even when accounting for changes in energy expenditure and physical activity during weight loss, we have found that there in some individuals there is a large difference between the weight loss and the amount of calories we can measure; that is some individuals lost more weight than expected based on the calorie deficit. We are investigating factors which may explain this difference. . Recruitment for both studies is ongoing.