'The Batman' actor insisted he has never struggled with his body image but has tried a number of "fad" diets and once opted for an unusual "detox" featuring nothing but one foodstuff, reports femalefirst.co.uk.

He said: "I have basically tried every fad you can think of, everything except consistency. I once ate nothing but potatoes for two weeks, as a detox. Just boiled potatoes and Himalayan pink salt. Apparently it's a cleanse... you definitely lose weight.

"And I tried to do keto once. I was like, 'Oh, there's a diet where you just eat charcuterie boards and cheese all the time?' But I didn't realise that you can't have beer as it completely defeats the purpose."

The 36-year-old star is concerned about the pressure men face to look a certain way and admitted it can be "extraordinarily addictive" to diet or exercise too much.

He told ES magazine: "Yeah, it's crazy. And it's very, very easy to fall into that pattern as well, even if you're just watching your calorie intake, it's extraordinarily addictive -- and you don't quite realise how insidious it is until it's too late."

When it comes to his own workout regime, the 'Lighthouse' star finds it an awkward topic of conversation.

He explained: "It's quite embarrassing when you get into a pattern of answering questions about your workout because there'll always be a guy who's in better shape than you.'

Meanwhile, after spending months doing research, Robert - who is in a relationship with Suki Waterhouse - is determined to get a dog this year.

He said: "I've spent so many hours looking at pictures of different dogs, I mean literally for months and months, so if I don't get one it'll be a colossal waste of time. I mean, I really went in."