Hill J O
Department of Pediatrics, Vanderbilt University, Nashville, TN 37232.
Int J Obes. 1990;14 Suppl 1:31-45; discussion 45-7.
We previously developed a model of dietary obesity in adult male rats where duration of feeding a high fat diet (HFD; 60 percent of calories from fat) influences reversibility of the obesity following a reduction in dietary fat. In the model, rats fed the HFD for 4 months show an apparent complete reversal of obesity when switched to a low fat diet (LFD; 14 percent of calories from fat), but rats fed the HFD for 7 months show persistent obesity even when switched to the LFD. This model of dietary obesity is useful for studies of energy balance and energy requirements during obesity development and reversal. In the present study, rats fed the HFD for 4 or 7 months were switched to the LFD and, after weights stabilized, were subjected to food restriction followed by ad libitum refeeding. Food restriction (15 g/day of the LFD, or about 60 percent of usual control food intake) continued until body weights of the groups stabilized at new, reduced levels (about 2-2.5 months). This was followed by ad libitum refeeding of the LFD for 3--4.5 months. Rats fed the HFD for 4 months showed complete obesity reversal after 2 months of eating the LFD. They showed a similar response to food restriction to LFD controls, but surprisingly regained significantly more body weight, body fat and total body energy during refeeding than LFD controls. Rats fed the HFD for 7 months remained heavier and fatter than LFD controls after 2 months of eating the LFD. Despite losing more carcass energy than controls during food restriction, their body weights and body energy content stabilized at higher levels than LFD controls. During refeeding, they regained their obese state relative to controls. These results demonstrate that: (1) the duration of HFD feeding is an important factor in the reversibility of the obese state; (2) sustained HFD feeding produces an obese state that is defended more by a greater restoration of carcass energy during refeeding than by a preservation of carcass energy during food restriction; (3) sustained obesity appears to produce some reductions in energy requirements; (4) even a brief period of obesity may leave the rats prone to reattain an obese state when body weight is challenged.
我们之前建立了成年雄性大鼠饮食性肥胖模型，在此模型中，喂食高脂饮食（HFD；脂肪提供60%的热量）的持续时间会影响饮食脂肪减少后肥胖的可逆性。在该模型中，喂食HFD 4个月的大鼠在改为低脂饮食（LFD；脂肪提供14%的热量）后，肥胖状况明显完全逆转，但喂食HFD 7个月的大鼠即使改为LFD后仍持续肥胖。这种饮食性肥胖模型对于研究肥胖发生和逆转过程中的能量平衡及能量需求很有用。在本研究中，喂食HFD 4个月或7个月的大鼠改为LFD，体重稳定后，先进行食物限制，然后随意再喂食。食物限制（每天15克LFD，约为正常对照食物摄入量的60%）持续到各组体重稳定在新的较低水平（约2 - 2.5个月）。之后对LFD进行3 - 4.5个月的随意再喂食。喂食HFD 4个月的大鼠在食用LFD 2个月后肥胖状况完全逆转。它们对食物限制的反应与LFD对照组相似，但令人惊讶的是，再喂食期间体重、体脂和全身能量的恢复量显著高于LFD对照组。喂食HFD 7个月的大鼠在食用LFD 2个月后仍比LFD对照组更重、更胖。尽管在食物限制期间 carcass能量损失比对照组更多，但其体重和身体能量含量稳定在高于LFD对照组的水平。再喂食期间，它们相对于对照组恢复到肥胖状态。这些结果表明：（1）喂食HFD的持续时间是肥胖状态可逆性的一个重要因素；（2）持续喂食HFD会产生一种肥胖状态，再喂食期间通过更多地恢复 carcass能量来维持这种状态，而不是通过食物限制期间保存 carcass能量来维持；（3）持续肥胖似乎会使能量需求有所降低；（4）即使是短暂的肥胖期，当体重受到挑战时，大鼠也可能容易再次达到肥胖状态。
