Fasting is an act of willing abstinence or reduction from certain or all food, drink, or both, for a period of time, week or days. Other fasts may be only partially restrictive, limiting particular foods or substances. The fast may also be intermittent in nature. Metabolic changes toward the fasting state begin after absorption of a meal (typically 3-5 hours after a meal); "post-absorptive state" is synonymous with this usage, in contrast to the "post-prandial" state of ongoing digestion. An absolute fast is normally defined as abstinence from all food and liquid for a defined period, usually a single day (24 hours), or several days. A journal is a periodical publication intended to further progress of science, usually by reporting new research. Most journals are highly specialized, although some of the oldest journals publish articles, reviews, editorials, short communications, letters, and scientific papers across a wide range of scientific fields.