In 1961 - and now too, for that matter - people sometimes liked to turn to meal replacement bars, if they were particularly rushed and just wanted to grab something, because you can't just shove an egg white omelet in your purse. In that pre-granola-bar age, what sort of things might you have grabbed? How about a Taper Diet Bar, approved by the astronauts? Ever heard of it? Me neither; and there's very very little online about them - as far as I could tell, just this 1961 advertisement. I remember Space Sticks from 1969, after the moon landing (not a diet food per se, but a snack that was supposed to make you feel as adventurous as Neil Armstrong et al), but not the Taper Diet Bar.
The Taper Bar came in three flavors: Lemon, Chocolate and Spice. They contained 416 calories and was scored so that you could break it into 4 pieces of exactly 104 calories each. This of course makes you wonder what precisely was in those 16 extra calories. Maybe they just made it up to make things sound like they had been calibrated exactly by the research scientists. You were supposed to eat three Taper Bars a day (which was 1248 calories exactly) and make sure to chug lots of water, black coffee or tea, and "dietetic soft drinks." I think that would have been OK once in awhile, not three times a day. I might have tried these in 1961 (if it hadn't been for obstacles like not having been born yet), but as a rule, I prefer sticking to salads, and fruit - and yes, the wildly un-portable egg white omelet.