Well, I seriously doubt it was from the breakfasts described. 40 years ago, people ate very differently. Note that TMOliver's list is protein heavy, and mostly savory not sweet. Compare that with all the empty, sweet carb we consume today. On a hot summer day, an 8-oz bottle of Coke (made with real sugar) was a rare treat, now the 44-oz, corn syrup sweetened drink is the norm, and folks consume them all day, every day. People mostly ate at home, imbibing smaller portions and recycling leftovers till they were gone. Even for upper middle class families it would be rare if they ate meat at every meal. Now the only meal not getting a heavy dose of meat is breakfast, where we like our sweetened cereals and high-fat granola bars for their convenience.

What TMOliver is describing is not everyday eating, but eating in better hotels or on planes of yesteryear. A special treat, because the cost of travel was so high.