Livestock production has been stigmatized based on the production of greenhouse gases (GHG), mainly methane gas (CH4 ). However, most of the population does not know the real numbers of the contribution of each economic sector to the production of these gases all over world. The United Nations (UN) estimates that the world population will reach 8.6 billion in 2030 and 9.8 billion in 2050, bringing the need to increase the production of food for humans and consequently animal consumption. Within the CH4 production mitigation strategies, the dietary manipulation is a simple and practical approach, which can guarantee better productivity, as well as reducing CH4 emissions by up to 40%. There is a possibility to classify dietary protein in relation to the place of the animal use, that is, it can be called rumen degraded protein (RDP) or rumen undegradable protein (RUP). On the other hand, it is known that the ruminal fermentation of carbohydrates and proteins lead to the cattle´s production of enteric CH4 . In such a way, the use of RUP could limit the growth of methanogenic microorganisms due to the low availability of H2 and methyl groups in the rumen for its metabolism, consequently reducing the CH4 emissions. This review aims to present details of ruminal metabolism and the results of recent studies using RUP sources to reduce CH4 emissions in ruminants.