"Surprisingly we saw the same decreases in LDL cholesterol, that's the bad cholesterol, and in triglycerides, and also in blood pressure," Varady said in the BBC documentary. "In terms of cardiovascular diseases risk, it didn't matter if you were eating a high or low fat diet."
"Another big surprise," she continued, "was that after a day of fasting, people rarely gorge themselves on their feed days."
Instead of making up for all the lost calories, participants in the study ate just 10 percent more on feed days.
So when Mosley created the Fast Diet, he came up with a human diet plan to see if he could mimic the results he found in American labs. Over time, Mosley found that more than his waistline was changing.
"My taste buds have altered significantly," he said. "I actually tend to eat-- I still eat fish and chips…[but] It has had a dramatic effect on my body."
But there are nutrition experts who are concerned that it is too big a leap to go from "patient zero" to a runaway bestseller with derivative books also making waves. Keith Ayoob, an associate professor at Albert Einstein College of Medicine's department of pediatrics and child development, worries about nutritional deficiencies and the prospect of people taking the diet to the extreme.
"[The Fast Diet] is anecdotal, based on [Mosley's] experience, that's an opinion," Ayoob said. "I like to make recommendations that are based on good solid science and I'm not there yet."
But over the course of two months, Mosley said he lost nearly 20 pounds on his Fast Diet and his overall health improved.
"My body fat went down from 28 percent to 20 percent, and my blood glucose went down from diabetic to normal," he said. "My cholesterol went down from needing medication to normal."
"What I had was visceral fat, fat in the gut," he added. "So if you get rid of that then you also significantly reduce your risk of diabetes and heart disease."
Mosley said there is no evidence that fasting leads to eating disorders, but he warned pregnant women, anyone under the age of 20, under-weight people and those who suffer from eating disorders to steer clear of the Fast Diet.