this is what it says on the CD website:
A few people are prone to cramp while using the Diet as their Sole Source of nutrition. It is not caused by the diet itself, but by the increased throughput of fluid in the body’s tissues. The muscle spasms result from changes in sodium levels as the water shifts between cells. The remedy for most people is to keep warm, whilst a drink of slimline tonic water just before bedtime may also help, as it contains quinine – as may "Crampex" tablets.