A nutritional composition comprises fat, protein and carbohydrate such that the fat provides from about 60 to about 90 % of the total calories of the composition, the protein provides from about 10 to about 30 % of the total calories of the composition, and the carbohydrate provides from about 0.1 to about 15 % of the total calories of the composition, and the composition comprises from about 0.01 to about 10 wt % beta-hydroxy-beta-methylbutyrate (HMB). A method of achieving or sustaining metabolic ketosis in an individual comprises administering the nutritional composition to the individual. A method of maintaining lean body mass and muscle strength in an individual during dietary ketosis comprises administering the nutritional composition to the individual.