I came across this slimming diet "Sensible Slimming in Practice", which was devised by the New Zealand Department of Health and was published in the New Zealand Home Journal 10 September 1948.
This was aimed at housewives and I really don't see that there would be many, if any over-weight women with wartime rationing. High energy foods such as sugar and butter were rationed so you wouldn't over eat these foods. There weren't all the labour saving kitchen appliances that we have now so cooking was physically more demanding so you would burn more calories just preparing your families meals.
But in 1948 New Zealand's Department of Health did start promoting healthier eating and food hygiene.