Factors which predict variance in weight change

为了研究能量消耗如何随着喂养过度和喂养不足而变化，正在进行以下研究。在一项研究中，在仔细校准体重维持EE后，个体在呼吸室中进行一系列24小时EE的测量，其中他们禁食或过度喂食（体重维持需求的200%）一系列常量营养素含量不同的饮食。这是为了进一步研究低蛋白或高蛋白饮食是否可以改善适应性产热的招募检测。此外，还进行行为、代谢和激素测试，以检查相关特征，并调查EE变化的机制。这些人还将接受长期随访，以了解哪些因素可预测体重变化。 来自完成这项研究的前19个人的结果发现，禁食和过度喂养的能量消耗变化是可重复的。此外，在那些过度喂养正常蛋白质、高脂肪或高碳水化合物饮食的人中，过度喂养导致的能量消耗增加最高。能量消耗没有显着增加低蛋白饮食。根据在禁食和过度喂养期间测量的能量消耗的差异，可以计算食物的热效应（TEF）。我们发现TEF与肥胖呈负相关。因此，TEF可能易导致体重增加或适应体重增加。由于肥胖的增加可能会阻止经腹热损失，这可能会增加TEF，我们正在研究中央绝缘对EE和TEF变化的影响与过度喂养。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测长期体重增加。 由于最近发现的棕色脂肪在人类的存在和它可能在产热作用，我们进行了正电子发射扫描标记葡萄糖。由于棕色脂肪被低温激活，我们已经确定，在暴露于16摄氏度2小时后，我们可以看到棕色脂肪。然后，我们目前正在研究在冷暴露后具有可视化棕色脂肪的个体是否在过度喂养后具有可视化棕色脂肪。在我们的代谢室中，在冷暴露后，通过使用高脂肪正常蛋白质饮食，使个体过量摄入其能量需求的200%，从而显示出可见的棕色脂肪。第二天早上，他们接受了PET-CT扫描;这是在一些人早餐前（大约12小时后，他们的最后一顿饭）和一些人在类似的早餐后（大约4小时后，他们的最后一顿饭）。我们没有发现任何证据表明，在高脂肪过度喂养后，过度喂养会激活棕色脂肪，这表明棕色脂肪不会介导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，棕色脂肪是否会被激活。 在一项相关的研究中，在测量了进食过量和进食不足的EE后，以及在经历了一系列代谢和行为测试（包括肌肉和脂肪活检）后，个体被允许接受为期6周的住院饮食方案，包括进食不足（对于超重和肥胖个体）或过度进食（对于瘦的，肥胖抵抗个体）。在住院研究期间，仔细测量食物摄入、能量消耗和能量损失的所有方面，以确定体重增加或减轻的差异是否可归因于适应性产热或其他因素的募集。我们目前已经完成了12个人谁经历了减肥研究。我们没有发现任何关联之间的初始能量消耗的变化与过度喂养和禁食和体重减轻。然而，我们已经能够计算出每个人的卡路里平衡（摄入的卡路里量与排泄的卡路里量），并将其与整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，在一些人中，体重减轻和我们可以测量的卡路里量之间存在很大差异;也就是说，有些人的体重减轻比基于卡路里不足的预期要多。我们正在研究可能解释这种差异的因素。 . 两项研究的招募正在进行中。

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.