Metabolic rift is a theory of ecological crisis tendencies under the capitalist mode of production that sociologist John Bellamy Foster ascribes to Karl Marx. Quoting Marx, Foster defines this as the "irreparable rift in the interdependent process of social metabolism". Starting with his book Marx's Ecology: Materialism and Nature, Foster argues that Marx theorized a rupture in the metabolic interaction between humanity and the rest of nature emanating from capitalist agricultural production and the growing division between town and country.

Foster, rather than Marx, coined the term "metabolic rift". Foster argues the theory develops from Marx's earlier work in the Economic and Philosophical Manuscripts on species-being and the relationship between humans and nature. Metabolism is Marx's "mature analysis of the alienation of nature" and presents "a more solid—and scientific—way in which to depict the complex, dynamic interchange between human beings and nature, resulting from human labor."

As opposed to those who have attributed to Marx a disregard for nature and responsibility for the environmental problems of the Soviet Union and other purportedly communist states, Foster sees in the theory of metabolic rift evidence of Marx's ecological perspective. The theory of metabolic rift "enabl[ed] [Marx] to develop a critique of environmental degradation that anticipated much of present-day ecological thought", including questions of sustainability as well as the limits of agricultural production using concentrated animal feeding operations. Researchers building on the original Marxist concept have developed other similar terms like carbon rift.

Marx's writings on metabolism were developed during England's "second" agricultural revolution (1815–1880), a period which was characterized by the development of soil chemistry and the growth of the use of chemical fertilizer. The depletion of soil fertility, or "soil exhaustion", had become a key concern for capitalist society, and demand for fertilizer was such that Britain and other powers initiated explicit policies for the importation of bone and guano, including raiding of Napoleonic battlefields and catacombs, British monopolization of Peruvian guano supplies, and, in the United States, "the imperial annexation of any islands thought to be rich in [guano]" through the Guano Islands Act (1856).

Foster argues that Marx's theory drew heavily on contemporary advances in agricultural chemistry unknown to earlier classical economists such as Ricardo and Malthus. For them, different levels of soil fertility (and thus rent) was attributed "almost entirely to the natural or absolute productivity of the soil," with improvement (or degradation) playing only a minor role.

German agricultural chemist Justus von Liebig, in his Organic Chemistry in Its Applications to Agriculture and Physiology (1840), presented the first convincing explanation of the role of soil nutrients in the growth of plants. In 1842, Liebig expanded the use of the term metabolism (Stoffwechsel), from referring to material exchanges in the body, up to the biochemical processes of natural systems.

Foster argues that Liebig's work became more critical of capitalist agriculture as time went on. From the standpoint of nutrient cycling, the socio-economic relationship between rural and urban areas was self-evidently contradictory, hindering the possibility of sustainability:

If it were practicable to collect, with the least loss, all the solid and fluid excrements of the inhabitants of the town, and return to each farmer the portion arising from produce originally supplied by him to the town, the productiveness of the land might be maintained almost unimpaired for ages to come, and the existing store of mineral elements in every fertile field would be amply sufficient for the wants of increasing populations.