Despite Matthew McConaughey's insistence that his rapid weight loss for the film "Dallas Buyers Club" was "a fun adventure," he reveals that there was a point when his body literally started shutting down. 

Speaking with Radio Times, the 44-year-old says that after losing more than 40lbs, his vision started deteriorating. "As soon as I hit 143lb, I started losing my eyesight.

"You have to reprogram all of your habits, and the days get so long. You think it must be lunchtime already, and it’s only 9.30 in the morning," he added. "I kept a diary of my nutrition the whole way through, and it is something I will probably share at some point because it was quite the adventure."

Additional side effects included a loss of sex drive, irritability, and - one bonus - increased mental agility. 

“Whatever power and energy I lost from the neck-down, I got that much more from the neck-up,” he told The Daily Beast. “I was incredibly turned on, and very sharp.”

McConaughey's eating regimen, which allowed him to lose seven pounds per week, consisted of tapioca pudding with a very small spoon, diet coke, egg whites, and a piece of chicken. 

"My body resembled a baby bird with its mouth open, crying, ‘Feed me, feed me,’ and you realize momma bird ain’t going to feed you. It’s hard," he said. 

Despite interest in extreme weight loss, nutrionists urge people to avoid celebrity crash diets and instead focus on a routine that will allow you to lose pounds naturally and safely. 

“You don’t want to be losing more than one to two pounds a week,” Hollywood food coach Kathy Kaehler told the UK Telegraph. “Anything beyond that is unrealistic to maintain. Yo-yo dieting doesn’t lead to success because it affects your metabolism and over time you will gain more body fat. I hate even using the word diet because it starts with the letters D-I-E.”

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Michael d'Estries ( @michaeldestries ) covers science, technology, art, and the beautiful, unusual corners of our incredible world.

Matthew McConaughey's crash diet almost made him blind
Actor says that as soon as he hit 143 pounds, he started to lose his eyesight.