The low efficiency of animal protein (meat products) production is one of the main concerns for sustainable food production. However, meat provides high-quality protein among other compounds such as minerals or vitamins. The use of meat extenders, non-meat substances with high protein content, to partially replace meat, offers interesting opportunities towards the reformulation of healthier and more sustainable meat products. The objective of this review is to give a general point of view on what type of compounds are used as meat extenders and how they affect the physicochemical and sensory properties of reformulated products. Plant-based ingredients (pulses, cereals, tubers and fruits) have been widely used to replace up to 50% of meat. Mushrooms allow for higher proportions of meat substitution, with adequate results in reduced-sodium reformulated products. Insects and by-products from the food industry are novel approaches that present an opportunity to develop more sustainable meat products. In general, the use of meat extenders improves the yield of the products, with slight sensory modifications. These multiple possibilities make meat extenders’ use the most viable and interesting approach towards the production of healthier meat products with less environmental impact.