The phrase "most alimental" refers to something that provides the most nourishment, sustenance or healthful qualities. Its antonyms would include words like inadequate, malnourishing, unhealthy, injurious or insubstantial. For example, fast food is known to be malnourishing and unhealthy, so it's antonymous to the phrase "most alimental." Foods that are high in fat, sugar, or salt are also insubstantial and injurious, making them undeserving of the title "most alimental." Similarly, certain substances such as drugs, alcohol and tobacco are harmful to the body and often have no nutritional value making them completely opposed to the notion of "most alimental.