基础代谢率（英语：basal metabolic rate，首字母缩写BMR）是指在自然温度环境中，恒温动物（比如人）的身体在非活动的状态下，处于消化状态（肠胃充满食物，分解作用大于合成作用），维持生命所需消耗的最低能量。这些能量主要用于保持各器官的机能，如呼吸（肺）、心跳（心脏）、腺体分泌（脑及其他神经系统）、过滤排泄（肾脏）、解毒（肝脏）、肌肉活动等等。基础代谢率会随着年龄增加或体重减轻而降低，而随着肌肉增加而增加。疾病、进食、环境温度变化、承受压力水平变化都会改变人体的能量消耗，从而影响基础代谢率。

Basal metabolic rate (BMR) is the minimal rate of energy expenditure per unit time by endothermic animals at rest. (McNab, B. K. 1997). On the Utility of Uniformity in the Definition of Basal Rate of Metabolism. Physiol. Zool. Vol.70; Metabolism refers to the processes that the body needs to function. Basal Metabolic Rate is the amount of energy expressed in calories that a person needs to keep the body functioning at rest. Some of those processes are breathing, blood circulation, controlling body temperature, cell growth, brain and nerve function, and contraction of muscles. Basal metabolic rate (BMR) affects the rate that a person burns calories and ultimately whether you maintain, gain, or lose weight. Your basal metabolic rate accounts for about 60 to 75% of the calories you burn every day. It is influenced by several factors. BMR typically declines by 1-2% per decade after age 20, mostly due to loss of fat-free mass, although the variability between individuals is high.