跑步测试之后气喘吁吁,半天都没有胃口。可游完泳,几乎每个人爬上岸后脑子里都只有“我要饿死了!”都是全身运动,也都挺累的,两种活动对食欲的影响却完全相反,运动还能不能减肥了?


为什么游泳后那么饿?


相对于陆地上的跑步或骑单车,游泳有很多特殊优势。不仅减轻体重对肌肉骨骼的压力,运动中还可以动用全身肌肉,提高心肺功能。用游泳锻炼身体很不错,但减肥效果明显不如快走或骑单车[1]。对比游泳与跑步运动员的体型,前者通常更圆润一些。


游泳时能量消耗并不少,不减重还是因为吃太多。这种运动特殊在哪里,让食欲不减反增?


最容易引起怀疑的是水。浸在水中时能量消耗通常高于陆地,而且水中运动后吃得更多。但进一步区分水温,人们发现只有冷水增加消耗,温水(32~34℃)并没有类似作用[2, 3]。随着水温升高,运动后进食量逐渐减小,高至28℃以上时,游泳后才不会吃得更多[4]。而一般泳池温度都低于28℃,所以我们游泳之后总是那么饿。


其实不仅水温,陆地上的空气温度也影响代谢与食欲[5]。进行相同运动之后,我们吃东西的量会随环境气温升高而逐渐减少[6-8]。所以在水里还是空气中不是关键,温度才是游泳容易饿的原因。


运动减肥不是骗人的


除了游泳,多数运动在合适的强度和时间下,减肥效果还是不错的[9]。因为运动不仅增加能量消耗,还能短暂抑制食欲,不让我们多吃。这样出量增加入量不变,能量缺口大了减重就快[10]


坚持运动时间长了,不仅刚运动完的时候食欲降低,控制全天不吃多的能力也提高。吃同样的高能量食物之后,长期运动的人在之后几餐中比不运动的人吃得少。这种调节利于保持全天饮食能量不超标,不容易长胖[11]


运动在降低食量的同时,还能提高饮食质量。高脂肪及高糖食物对人的诱惑会在运动后减弱,但低能量的食物不受影响。饮食选择的变化可以帮助我们多吃营养健康的食物,减少长胖的高能量零食[12,13]


虽然运动可以通过抑制食欲帮助减肥和改善健康,但吃什么东西不完全决定于食欲[14]。很多人运动后虽然不饿,但想想刚才那么辛苦,觉得必须奖励自己点儿好吃的。总这么想的话,运动抑制食欲用处也不大了。


怎样运动能少吃


“哪种运动最减肥?”是很多人选择运动时最先考虑的问题。单独考虑抑制食欲的作用,有氧运动可能优于抗阻运动(举铁)。在有氧运动中,除了跳绳抑制食欲的效果更好,其他运动种类没有明显区别 [15-17]


不过运动类型的影响并不大,时间和强度才是最重要的。


1. 多坚持一会儿就不饿了


运动时间适当延长,抑制食欲的效果更好。比如把骑车时间从20分钟延长到40分钟,运动中能量消耗多了一倍,但不会因此多吃,所以减重更有效[18, 19]。如果想利用运动抑制食欲,中等强度运动最好坚持40分钟以上。


2. 累就对了,运动强度不能太低


很多人因为没空和无聊无法忍受这么长时间的运动,有个办法是增加强度。运动抑制食欲的效果和持续时间随着强度升高而增大[20-23]。在消耗能量相同的条件下,半小时高强度运动比一个小时低强度运动后吃得更少[24]。如果强度足够高,食欲降低持续时间可长至1~2天[25]。长期如此,高强度比低强度运动降低体重的效果更好[26]


虽然时间短了,但这么高的强度让有些人难以坚持。还可以把持续的运动改为间歇形式:之前固定速度跑步,现在变成全力冲刺一段,然后用慢跑或步行休息一会,再重复冲刺和休息。只要消耗的总能量相近,间歇运动抑制食欲的效果不比持续形式差,甚至更好(当强度非常高时)[26, 27]


想减肥可以用高强度运动降低食欲,希望增重的人也能用低强度运动改善胃口 [28] 。相对于静止不动,胃排空速度在高强度运动(心率>160次/分)中减慢,低强度运动(心率<120次/分)中反而加快。所以快跑后吃不下,散步比坐着不动食欲好[17]


运动强度与进食能量的关系丨参考文献[28]


抑制食欲的运动时间


关于最佳运动时间的争论,一直没有停止。如果仅考虑抑制食欲的效果,有研究显示上午运动优于下午[29]。但早中晚的时间点,不如运动与进餐的关系重要。


通常餐前运动降低饥饿感的效果更好,能量及脂肪吃得更少,这样容易减轻体重,也益于改善血脂水平[14,30]。餐后运动的优势在于维持血糖水平稳定,对糖尿病患者更有益。另外,每个人的肠胃对运动反应也不同,有人餐前举铁不舒服,也有人餐后跑步肚子疼。所以餐前还是餐后运动,要结合运动目标和自己身体情况来决定。


如果为了抑制食欲将运动安排在餐前,间隔时间不能太长。运动后30分钟内进食量会受到明显抑制,60分钟作用减弱,到180分钟时就基本消失了。不仅食欲,我们对脂肪的热爱程度也会随时间延长而恢复[10,31]。所以刚运动完吃得少,休息时间越长吃得越多,特别是高脂肪的食物。


综合来看,接近午餐时间运动,对抑制食欲及平衡能量最有益[14]。但对于个人,能保证规律运动又不会引起不舒服的时间才最好,不必过分纠结细节。


强度和时间配合好,除了游泳的多数运动都能用于抑制食欲。有了饱腹感,减重还需要控制其他生活习惯。另外,上面的建议都是针对降低食欲的,当运动的目的是改善身体健康、情绪、睡眠或提高体能时,可能需要不同的安排。


参考文献

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