Joanna Hall The 24 Hour Diet Lose up to 4lbs in a Day The UK's leading diet and fitness expert, Joanna Hall, shows you the healthy way to shed excess pounds in a day. This fantastic plan is a refinement on the typical low GI diet. It is complimented with a 20 day follow-on plan which builds up in very small steps, day by day. Joanna's mantra is: small steps make big changes.