New details about Jackie Kennedy's life and habits after the tragic passing of her husband are coming to light in a new book Jackie's Girl: My Life With The Kennedy Family from her former assistant and live-in nanny, Kathy McKeon.
McKeon, who worked for the former First Lady for 13 years and lived with the family at their 5th Avenue apartment for 11 years, became extremely close with Jackie and gave very personal details about their relationship.
She recalled in the book that the notoriously thin-framed First Lady was just "not a big eater" and maintained her thin physique through a very strict diet. In an excerpt shared with People ahead of the release, she talked about how difficult her husband's death was on Jackie.
"She never had much of an appetite," writes McKeon, "and the toll of the horror she survived was plain to see on her painfully thin frame."
Of course, the horror that McKeon is referring to is the death of President Kennedy, which rocked their family and the entirety of the United States.
McKeon often looked to the former First Lady for advice. When she gained weight, she said that Jackie took her to the kitchen and instructed the cook to make the same meals for her that she did for McKeon. It was a strict diet of a "boiled egg and tea for breakfast, cottage cheese with fresh fruit at lunch, and a poached chicken breast or fish, with a salad or steamed vegetables for dinner (with plain yogurt to snack on when she was hungry)."
PHOTOS: Jackie Kennedy through the years
Jackie Kennedy Onassis through the years
Jackie Kennedy Onassis through the years
(Original Caption) Mrs. Jacqueline Kennedy, wife of the President, smiles as she leaves the jet at Idlewild Airport that returned her to the U.S.A. on her flight from Athens, Greece. She left immediately for Washington, D.C., on the Kennedy private plane.
(Original Caption) Mrs. Jacqueline Kennedy (center) appears to be enjoying her vacation in these islands as she smiles at a well-wisher here June 9th. While in Greece, Mrs. Kennedy plans to do some water skiing and sun bathing just like any other tourist.
(Original Caption) Jackie and John Kennedy cut their wedding cake in 1953. (Photo by Brooks Kraft LLC/Sygma via Getty Images)
Jackie Kennedy the wife of American President John F. Kennedy, at home with their daughter Caroline, 1960. (Photo by ï¿½ Hulton-Deutsch Collection/CORBIS/Corbis via Getty Images)
Portrait de profil de Jackie Kennedy, circa 1960. (Photo by REPORTERS ASSOCIES\Gamma-Rapho via Getty Images)
circa 1960: Jacqueline Lee Bouvier Kennedy Onassis (1929 - 1994), wife of American president John F Kennedy and, after Kennedy's assassination, of Greek shipping tycoon Aristotle Onassis. (Photo by MPI/Getty Images)
Senator John F. Kennedy sits beside wife Jackie in Hyannisport. Kennedy is about to embark on a campaign tour for the presidential elections.
Jackie Kennedy. October 14, 1960. (Photo by William N. Jacobellis/New York Post Archives / (c) NYP Holdings, Inc. via Getty Images)
10th December 1960: Jackie Kennedy (1929 - 1994), the wife of the American President-Elect John F Kennedy with her son John Kennedy Jr (1960 - 1999). (Photo by Keystone/Getty Images)
Frank Sinatra escorting Jacqueline Kennedy to her box at a gala, held at the National Guard Armory in Washington DC, the night before the inauguration of President John F. Kennedy, 19th January 1961. The gala was staged by Sinatra to help pay off the campaign debts of Kennedy and the Democratic Party. (Photo by GAB Archive/Redferns)
President-elect John F. Kennedy and wife Jackie applaud at a pre-inauguration gala on January 19, 1960.
Jackie Kennedy and Nina Chruschtschowa are meeting at the reception and great dinner at Schï¿½nbrunn Palace during the two-day summit between Presidents John F. Kennedy and Nikita Khrushchev in Vienna. Schï¿½nbrunn. Wien 13. 3. Juni 1961. Photographie. (Photo by Votava/Imagno/Getty Images)
Second day of the visit of American President John F Kennedy and his wife Jackie to London, England. Jacqueline Kennedy leaving the London home of her sister Princess Lee Radziwill for the christening of her niece Anna Christina Radziwill. 5th June 1961. (Photo by Daily Herald/Mirrorpix/Mirrorpix via Getty Images)
Nikita Khrushchev and Jackie Kennedy share a light moment during the summit meetings in Vienna between President John F. Kennedy and Soviet leader Khrushchev, Vienna, Austria, June, 1961. (Photo by Underwood Archives/Getty Images)
(Original Caption) Mrs. Dwight D. Eisenhower (left) calls out to an acquaintance among the newsmen, as she is greeted at the White House by Mrs. Jacqueline Kennedy today. The First Lady and her predecessor, who are honorary co-chairman of the National Cultural Center, will discuss future plans for the proposed center at a tea in the Executive Mansion.
7th June 1961: Jackie Kennedy (1929 - 1994), wife of president John F Kennedy, boards a BEA aeroplane at London airport. Accompanying her on the flight to Athens is her sister Lee Radziwill. (Photo by Jimmy Sime/Central Press/Getty Images)
(Original Caption) Flanked by the Presidents of two North American neighbors, Adolfo Mateos (left) of Mexico and John F. Kennedy, her husband, Jacqueline Kennedy takes center stage away from them here, June 29th. The Mexicans were just wild about Jackie. The 'vivas' for her were as loud and as fervent as for her husband on their triumphal arrival in this ancient Aztec capital. The Kennedys are here on a 48-hour visit.
381091 72: The President and Mrs. Kennedy ride in a parade March 27, 1963 in Washington. (Photo by National Archive/Newsmakers)
(Original Caption) Mrs. John F. Kennedy bids farewell to Nicaraguan Ambassador to the U.S., Guillermo Sevilla-Sacasa (right) and Dr. Jose Mora, Secretary General of the Organization of the American States, as she left the Pan American Union today. Mrs. Kennedy, Attorney General Robert K. Kennedy, and Senator Edward M. Kennedy attended the luncheon to discuss the proposed John F. Kennedy Memorial Library with Latin American officials.
(Original Caption) President John F. Kennedy applauds as his wife is introduced at a Chamber of Commerce breakfast, November 22nd. Later in the day, an assassin firing into the President's open car in Dallas hit the President and the Governor of Texas, John Connally.
Jackie Kennedy Onassis (Photo by Ron Galella/WireImage)
(Original Caption) Mrs. John F. Kennedy, chats with Mies Van Der Rohe, internationally known architect on 4/12. Architects, designers , and artists assembled here to discuss type and design of the $10 million memorial to be erected on the Harvard University campus at Cambridge, Massachusetts.
Jackie Kennedy And Her Sons At Gstaad - Jackie And Caroline In Gstaad, Switzerland, January 1966. (Photo by Andre SAS/Gamma-Rapho via Getty Images)
11/6/1967- Sihanoukville, Cambodia: Prince Norodom Sihanouk walking on red carpet with Jackie Kennedy prior to dedication of John F. Kennedy boulevard.
18th October 1968: Millionaire shipping magnate Aristotle Onassis (1906 - 1975) with his wife Jackie (Bouvier Kennedy, 1929 - 1994). (Photo by Central Press/Getty Images)
Jackie Kennedy Onassis during Jackie Onassis and Ari Onassis Sighting At Le Cote Basque - October 6, 1969 at La Cote Basque Restaurant in New York City, New York, United States. (Photo by Ron Galella/WireImage)
Jackie Kennedy Onassis during Jackie Kenendy Onassis Sighting - January 1, 1970 at La Cote Basque in New York City, New York, United States. (Photo by Ron Galella/WireImage)
Jackie Kennedy Onassis during Jackie Onassis At JFK Airport - March 1, 1970 at JFK Airport in New York City, New York, United States. (Photo by Ron Galella/WireImage)
Jackie Kennedy Onassis (Nina Ricci sunglasses, Gucci bag) in Paris, leaving Crillon Hotel, march 19, 1970. (Photo by RDA/Getty Images)
Caroline Kennedy & Jackie Onassis during Royal Ballet performing 'Sleeping Beauty' at Metropolitin Opera House in New York City, New York, United States. (Photo by Ron Galella/WireImage)
Jackie Onassis (1929 - 1994), widow of American President John F Kennedy and wife of Greek born Argentinian ship owner Aristotle Onassis, leaving Claridges Hotel in London. She is wearing a safari-style jacket over flared hipster trousers and a polo neck jersey. (Photo by Ted West/Getty Images)
Jackie Onassis during Jackie Kennedy and Family Shopping in Capri - August 24, 1970 in Capri, Italy. (Photo by Ron Galella/WireImage)
Jackie Kennedy Onassis, Caroline Kennedy, and John F. Kennedy Jr. (Photo by Ron Galella/WireImage)
Jackie Onassis, Joe Kennedy, and Ethel Kennedy during Funeral of Cardinal Cushing in Boston, Massachusetts, United States. (Photo by Ron Galella/WireImage)
Jackie Kennedy Onassis during Jackie Onassis At Caroline Kennedy's School Dinner - November 11, 1970 at La Cote Basque in New York City, New York, United States. (Photo by Ron Galella/WireImage)
Jackie Onassis (Photo by Tom Wargacki/WireImage)
Jackie Kennedy and Caroline Kennedy (Photo by Ron Galella/WireImage)
Jackie Onassis, Caroline Kennedy, Rose Kennedy, and Ted Kennedy (Photo by Ron Galella/WireImage)
Washington, D.C. May 14th 1976. Jackie Onassis and Alexandrje Orfila at The Kennedy Center (Photo by Tom Wargacki/WireImage)
Jackie Onassis during Caroline Kennedy's Graduation Party - June 6, 1973 at Kennedy Compound in Hyannisport, United States. (Photo by Tom Wargacki/WireImage)
Jackie Kennedy Onassis and Ethel Kennedy during RFK Pro Celebrity Tennis Tournament - August 23, 1975 at Forest Hills Stadium in New York City, New York, United States. (Photo by Ron Galella/WireImage)
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"The diet was almost exactly what Madam herself ate at home when she wasn't entertaining," explained McKeon.
But Jackie didn't stick to that diet forever. Once she met Onassis, Jackie reportedly let some things flow and enjoyed cocktail hour and late-night desserts.
"If she went into the kitchen and saw my brownies or chocolate chip cookies she would grab one and eat it right there," McKeon recalls. "Sometimes we'd crash into each other at night in the kitchen pantry. She didn't put on the light because she didn't want anyone to know she was in there!"
"She was eating ice cream out of the container with a big spoon," she says with a laugh. "Not a teaspoon but a big spoon! She was a lot of fun."