Living in a box for 44 days and running seven marathons in a week may, at first sight, have little to do with ensuring more ordinary mortals eat and exercise properly.
David Blaine spent five days in hospital after the stunt
David Blaine's 44 day-fast and Sir Ranulph Fiennes' example of extreme endurance showed how the body behaves under such circumstances.
But experts who were involved in the high-profile projects say they also offered clues as to how diet and exercise should be managed for everyone.
Doctors will present their findings to a conference at the Royal College of Physicians in London on Tuesday.
An estimated 18 to 40% of hospital patients are believed to be under-nourished.
Jeremy Powell-Tuck, who is professor of clinical nutrition at Barts and the London Queen Mary School of Medicine, treated magician David Blaine after he emerged after 44 days suspended in a Perspex box above London.
Professor Powell-Tuck supervised the "re-feeding" period, where Blaine's body was gradually re-introduced to food again, and he monitored the effects for the eight months it took David Blaine to get back to his original weight.
He told BBC News Online it was useful to be able to study someone who was malnourished, but who was not affected by disease.
"David Blaine had lost 25% of his bodyweight, but he still had a healthy body mass index", he said.
Body mass index (BMI) is calculated by dividing weight in kilograms by the square of your height in metres.
Blaine's BMI was 21.6 when he emerged from the box - which would normally be classed as healthy - but it had fallen from 29.
Professor Powell-Tuck added: "It shows doctors need to ask what a person's normal weight is and what their weight is now. If they have lost more than 10% of their bodyweight, there is a problem."
David Blaine also became deficient in B vitamins.
"It showed that in just 44 days, someone can become dangerously deficient in B vitamins, which can lead to short-term problems.
"And if someone is undergoing re-feeding treatment in hospital, it is important they are also given vitamins, which doesn't always happen."
The conference will also hear from Dr Mike Stroud of the Institute of Nutrition in Southampton.
In 2003, Dr Stroud completed seven marathons in seven days across seven continents alongside the explorer Sir Ranulph Fiennes.
Dr Mike Stroud with his marathon partner Sir Ranulph Fiennes
Dr Stroud said: "I have shown that, when you're doing a great deal of exercise, the idea that exercise cannot induce weight loss is ridiculous.
"I was eating 5,500 calories a day when I crossed the Antarctic - but I lost three stone."
"It's an extreme example, but it shows that the idea that weight loss is all about diet and not activity has been over-emphasised."
Dr Stroud said the chances of an overweight but active individual having a serious heart attack or stroke are raised by only 20% compared to a lean active individual, whereas an inactive lean individual is close to being at 300% greater risk.
He said people should not focus on having to go to the gym to lose weight, but should build exercise - such as walking - into their everyday lives.
Professor Peter Kopelman, Chair of the RCP's Nutrition Committee said the conference would help raise the profile of a topic which received too little attention
"Nutrition remains a Cinderella subject for many health professionals.
"Doctors all too often fail to recognise the contribution that malnutrition, whether it be under- or over-nutrition, makes to disease processes."
He said the conference would also examine how to address the epidemic of obesity in terms of prevention and management.