The Daily Star's FREE newsletter is spectacular! Sign up today for the best stories straight to your inbox Sign up today! Thank you for subscribing See our privacy notice Invalid Email

(Image: GETTY/MICHAEL HAVIS)

Hyeong-soo Kim said the mysterious Longevity Institute where he worked had the sole purpose of pushing back the leader's death.

And with the lifestyle of North Korea's leaders being notorious for its huge meals, that meant a constant fight with cardiovascular disease and diabetes.

It left researchers desperate to study other obese people, but with North Korea unable to feed its population, they were forced to spy on overweight foreigners instead.

(Image: MICHAEL HAVIS)

The former researcher, who fled North Korea in 2009, worked at the institute when Kim Jong-un's father, Kim Jong-il, still ruled the hermit kingdom.

He told Daily Star Online: "There were 130 researchers that came from the engineering and medical departments of Kim Il-sung University.

"Also there's a research information centre that consists of diplomats or researchers that come from foreign universities.

"The institute is guarded 24/7 and also there is a very high four-metre wall that is electrified."

He continued: "They developed food products because Kim Jong-il had cardiovascular disease and diabetes.

"The two Kims were rather obese, so they monitored and researched people that were obese, which is hard in North Korea.

"Because most of the people are going through malnutrition, they had to study and research the obese superiors or the political leaders.

"Even foreign diplomats or correspondents that come to North Korea were actually researched. These people didn't even know they were being studied."

(Image: GETTY)

When joining the institute, Mr Kim had to sign a confidentiality clause pledging to never reveal its secrets, but now he’s safe in South Korea.

Yet he saw one colleague who did gossip about their work sent with his whole family to North Korea's concentration camps in 1991.

Now able to speak out, Mr Kim has already revealed how North Korea massaged cows and fed them beer to make their meat more tender for the leader.

(Image: MICHAEL HAVIS)

He also told us that medicine donated by the international community was auctioned off by the regime, with tuberculosis drugs fetching a particularly high price.

Mr Kim told Daily Star Online: "For one month, it would cost about $200 which is the equivalent of what a labourer would make in five years in North Korea.

"So of course I have seen a lot of my relatives having children that would die of tuberculosis because they couldn't pay for the medication."