Two brands of slimmer's bread were popular in the '70s, one was Nimble and the other the perhaps less famous Slimcea. The advertising jingle for the latter was 'Show them you're a Slimcea girl'.
It has attained fame in my family due to the adoption of Slimcea by my very large Welsh grandma in an attempt to lose weight. She somehow got the wrong end of the stick and imagined that the more Slimcea she ate, the thinner she'd get- that it contained some sort of magical ingredient that made you slim! She was very dismayed when her heavy consumption of the product actually made her GAIN weight rather than lose it, declaring "I don't understand it, I'm eating no END of Slimcea!"