Masur or lentil is a bushy, annual shrub plant that is popular for its lens shaped seeds, which are consumed as food in stew or other forms all over the world. These seeds have a vast range of colors from yellow to redorange to green, brown and black and also have second highest levels of proteins and fiber after soybeans. The thin lentil plant, which is named Lens culinaris botanically, comes from the legume family and gains a height of 12 to 24 inches at maturity.

With about 30% of their calories from protein, lentils have the third-highest level of protein, by weight, of any legume or nut, after soybeans and hemp.[4] Proteins include the essential amino acids isoleucine and lysine, and lentils are an inexpensive source of essential protein in many parts of the world, especially in West Asia and the Indian subcontinent, which have large vegetarian populations. Lentils are deficient in two essential amino acids, methionine and cysteine.

Lentils also contain dietary fiber, folate, vitamin B1, and minerals. Red (or pink) lentils contain a lower concentration of fiber than green lentils (11% rather than 31%). Health magazine has selected lentils as one of the five healthiest foods.

The low levels of Readily Digestible Starch (RDS) 5%, and high levels of Slowly Digested Starch (SDS) 30%, make lentils of great interest to people with diabetes. The remaining 65% of the starch is a resistant starch that is classified RS1, being a high quality resistant starch, which is 32% amylose.

Lentils also have some anti-nutritional factors, such as trypsin inhibitors and relatively high phytate content. Trypsin is an enzyme involved in digestion, and phytates reduce the bio-availability of dietary minerals. The phytates can be reduced by soaking the lentils in warm water overnight.[citation needed]

Lentils are a good source of iron, having over half of a person's daily iron allowance in a one cup serving.