Converts of the caveman lifestyle advocate eating and exercising in ways that replicate how people in the Neolithic era might have. Photo: Li Hao/GT

What do film heartthrob Matthew McConaughey, screen siren Jessica Alba, and US Republican presidential hopeful Jeb Bush have in common?

According to a recent New York Times report, Bush, the 62-year-old former Florida governor and brother of former US president George W. Bush, is one of the latest high-profile converts to the paleo diet - a weight loss regime advocated by the two Hollywood stars.

Following the diet - which requires devotees to reduce or entirely remove processed foods, diary products, grains, legumes, alcohol and starchy vegetables from their daily intake, Jeb Bush has managed to shed 13.6 kilograms since last November, per the report.

The diet, proponents claim, is based upon what hunter-gatherers in the Paleolithic era, might have eaten. The theory is that such a diet is more suited to the human metabolism than modern diets - which proponents claim are responsible for a host of common health issues, including obesity, heart disease and diabetes.

Some advocates have taken its logic even further, adopting what they call a "caveman lifestyle," according to a September 2014 New York Times report. Besides consuming huge quantities of meat and little else, as they imagine their Paleolithic ancestors did, they fast between meals, to emulate the fallow periods between hunts, and engage in exercise routines meant to replicate chasing prey or running away from predators.

Eating only meat

Jiang Yu, a 27-year-old lawyer based in Beijing, said he had lost 5 kilograms since adopting the caveman lifestyle in October last year.

"I wanted to lose weight but kept failing because I struggled to eat less, especially less meat," said Jiang. "But the paleo diet is different, because you're encouraged to eat meat, and as long as it's lean meat, you can eat as much as you want."

At the beginning, Jiang said he adhered strictly to the rules of the paleo diet, but he now allows for a small quantity of grains and diary products.

"I don't think they're unhealthy, and maybe if cavemen did have access to them, their health might have been better," said Jiang.

What was important, said Jiang, was that he no longer ate any processed foods. "Ice cream and spicy beef jerky used to be my favorites, but now I have no feelings toward them," said Jiang. "Instead, I buy raw beef and cook it at home in the simplest way I can, which is healthier."

Shi Jie, a Beijing-based nutritionist, said she was completely in support of eliminating processed foods from daily consumption, and preparing food in a simple way or eating it raw to preserve its nutrients. But Shi was skeptical about some of the paleo diet's other claims. "Processed food usually contains a lot of harmful additives, such as excessive quantities of salt, fat, calories, and chemical additives," she said. "[But] lack of carbohydrate intake due to refusing to eat grains can be bad for health, and can adversely affect brain, bone and kidney function."

From a scientific nutritional view, said Shi, dietary variety was the basic foundation of good health, and the biggest shortcoming of the paleo diet was its lack of variety.

She pointed to the food pyramid endorsed by numerous countries including China as a good rough guide to how people should consume from different food groups, including diary products and grain.

"People following the paleo diet should know that although it might seem healthier than a modern diet, the average life expectancy of people [during the Paleolithic era] was only around 30 to 40 years," joked Shi. "[If people insist on following it], I would recommend doing it for no longer than three months at a time, with a month's rest in between, or it could lead to malnutrition."

Nutritionists advise against strict adherence to the paleo diet, which they say deprives the body of essential nutrients. Photo: Li Hao/GT

The wounds of battle

Conforming to the caveman lifestyle, Jiang said he also fasted every two weeks, subsisting on only water for about 30 hours on each occasion.

"It's a simulation of caveman life," said Jiang. "[Hunter-gatherers] would not always be able to find food, so they would regularly starve."

Jiang said he was part of an online QQ chat group with around 100 members that declared an allegiance to the caveman lifestyle. He said that some of its members were even more committed than him in replicating what they considered a hunter-gatherer's life to be like, going as far as donating blood to mimic the injuries and wounds a hunter-gatherer would sustain in the course of his travails.

He said that some members donated blood between one and three times a year, but it was a step too far for him personally. "I think it is a bit too extreme to replicate every detail of a caveman's life," said Jiang. "I follow it as much as I'm able to, and to the extent that I think is reasonable."

Shi dismissed the benefits of regular fasting, and said she thinks the idea of giving up blood for health purposes is absurd.

She said there were circumstances under which fasting could be beneficial in detoxing the body, but abrupt fasting in the way practiced by Jiang could upset biological balance, as well as triggering low blood sugar levels and dizziness. "It has to be done gradually," said Shi. "For the first week, perhaps fast for 6 to 8 hours, then the next week, for maybe 8 to 10 hours."

Shi said that a period of fasting for detoxing the body should not exceed 12 hours, and if the person starts to feel severe hunger or discomfort, it should immediately be ceased.

Running from tigers

The other major component of the caveman lifestyle, according to the New York Times, is exercising like a hunter-gatherer, which involves approximating the physical activities a prehistoric man might have engaged in, from "sprinting and jumping" to "leaping between boulders" and "scooting around the underbrush on all fours."

This philosophy toward exercise is summed up by John Durant, founder of Paleo NYC and Barefoot Runners NYC, in his 2013 book, The Paleo Manifesto: Ancient Wisdom for Lifelong Health: "Other animals don't 'exercise' so much as they either play or just do what is required to survive. Birds fly. Fish swim."

The article describes Durant and other advocates of cavemen exercise as running barefoot and bare-chested late at night.

Jiang said he sometimes adopts the mindset of being a hunter-gatherer when he goes running. "I go running every night, and for 10 minutes I will run as fast I can, as if I'm running for my life, as if I'm being chased by a tiger," he said. "I can feel energy and life pulsing through me during these moments."

Another popular form of exercise endorsed by followers of the caveman lifestyle is CrossFit, a strength and conditioning program that emphasizes high-intensity workouts targeted toward optimizing "functional movement," according to a report published in the Observer last July.

A June 2014 Time Magazine article noted that there are over 10,000 gyms affiliated with CrossFit around the world, but Wang Yangguang, a private fitness instructor at Hosa Fitness in Beijing, said that the program was not suitable for everyone.

"I think it's only appropriate for people who already have a certain level of fitness and physical prowess," said Wang. "For starters, it's impossible and maybe even harmful [for those who aren't fit] to force themselves to run as if they were fleeing from a tiger."

Wang said it was important that people choose an appropriate level of intensity for their fitness level, and if they did want to do high-intensity exercise, it was advisable to seek the guidance of a professional instructor. "Blindly doing strenuous exercise is dangerous, especially outdoors," said Wang.

"Poor form when exercising and exercising in unfamiliar environments can lead to injury and accidents," Wang said.