Breakfast meals vary widely in different cultures around the world, but often include a carbohydrate such as cereal or rice, fruit and/or vegetable, protein, sometimes dairy, and beverage.
Nutritional experts have referred to breakfast as the most important meal of the day, citing studies that find that people who skip breakfast are disproportionately likely to have problems with concentration, metabolism, and weight.
Breakfast has commonly been practiced worldwide and is a concept easily transferred between cultures, but there have been many regional interpretations over the years. In Medieval Europe, for instance, the basic format of meals differed from what is currently 'standard', in that only two meals were to be had; a heavy dinner at noon and a light supper, largely due to the influence of the Church.
However, exceptions existed, most notably for children and the infirm. They were allowed a small breakfast meal, and many labourers, farmers, and other physical workers also took the meal despite criticism and social pressure on them not to, and by the 15th century even the nobility had begun to ignore the rules and mores of polite society and took breakfast.
The earliest appearance in print of the idea that "breakfast is the most important meal of the day" occurs in the novella The Metamorphosis, published in 1915 by Franz Kafka, which includes the line, "for Gregor's father, breakfast was the most important meal of the day".
Some restaurants devote themselves to breakfast or have special breakfast menus. The field is dominated on one hand by greasy spoons, diners, cafés, cafeterias, and fast food places, and by hotels. However, some breakfast places resemble standard restaurants in procedure, selection, and price.