A

The food industry has promoted this claim for decades to sell breakfast cereal. But rigorous scientific studies have found no evidence that it’s true.

The idea that a hearty breakfast is good for your health dates back to the 1920s, when Edward Bernays, a public relations guru, led a nationwide media campaign encouraging people to start their mornings with bacon and eggs. One of Mr. Bernays’s clients at the time was Beech-Nut Packing Company, which sold bacon and other pork products.

In the decades that followed, dozens of observational studies reported that breakfast eaters tended to be leaner. Though these studies could not show cause and effect, many health authorities and food companies asserted that they proved that eating breakfast protects against weight gain.

But experimental studies that randomly assigned people to eat or skip breakfast have found no such thing. One of the most recent, published in February, found no difference “in weight change and most health outcomes” between people assigned to eat breakfast for six weeks and those assigned to skip it.

“Whether or not you have breakfast in itself is not going to impact your body weight,” said James Betts, an author of the study and an associate professor of nutrition and metabolism at the University of Bath in England.

Dr. Betts said that unlike randomized trials, observational studies of breakfast consumption could be misleading. They show, for example, that people who eat breakfast also follow other behaviors associated with good health. They tend to drink and smoke less, consume less sugar, eat more fiber and exercise more than those who skip a morning meal.

“All we know from observational studies is that people who have breakfast are leaner,” he said. “But it may be other factors that are the reason.”