It takes 7,000 calories per day to build a body like Tarzan's.

That's almost 30,000 kilojoules or three times the average daily recommended energy intake for a man.

Alexander Skarsgard, who landed the iconic role in the new The Legend of Tarzan film, told that he did "nothing but eating and training" for eight months to prep for the role.

"We did it in different phases, the first was to bulk up and try and put on some weight," he said while promoting the movie in Sydney. "The diet consisted of 7,000 calories per day of mostly meat and potato. For the first three months, I ate constantly. I was still shooting True Blood at the time and they gave me a Tupperware box with cold steak and potatoes and salad I would walk around on set constantly eating."


The second phase involved a very strict diet of six small meals a day, which he says sent him "crazy" with hunger.

And the meals were also bland, despite his personal chef's best efforts to make the food tasty without the use of any dairy products, butter or rich sauces.

"No sugar, no dairy, no fast carbs," he said of the diet. "Steak, chicken, smoked fish, we had a great chef which saved my life because I like to eat ... but with that said for the first eight months, you can't eat until you're full.

"The meals were so small that it was just what I needed to get through the day, but I was like 'ahhh', I went crazy. I would walk around and look at my watch constantly thinking, when's my next meal, that was the highlight of my day."

Skarsgard, who stars alongside Margot Robbie in the film, says he was so strict with his diet that he didn't have a single cheat day for five months.

"I had no cheat days in the beginning, I was terrified, I was so determined, I had to be very diligent and work really hard because I didn't know how my body would respond to this because I hadn't done anything like this before.

Margot Robbie and Alexander Skarsgard star in the movie The Legend of Tarzan.
Margot Robbie and Alexander Skarsgard star in the movie The Legend of Tarzan.

"I just made sure I did exactly what my trainer told me to do, I tried to be a good boy. Towards the end of the shoot, when I felt like we knew what we were doing and what worked and didn't work, he would allow me a cheat meal here and there."

The 39-year-old Swedish actor recalls a time he was so desperate for a comfort mean that he cried in an Italian restaurant with his trainer.

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"About five or six months into it, it was a day off and we were at the gym and my trainer Magnus saw that my will to live was gone so he basically said, 'let me take you to lunch' and he took me to an Italian restaurant and sat me down and said 'order whatever you want' and I hadn't had bread or pasts in six months and I ordered pasta and ate it and it was the most delicious meal ever and he said 'are you still hungry' and I was like 'yeah' so I ordered a pizza and tiramisu and it was heaven."

The Legend of Tarzan opens in cinemas on July 30.