Spencer, 25, said he felt "ashamed" of how he looked and felt "decidedly lumpy" before taking action to shed the pounds.
In these new pictures, the lothario can be seen showing off his body before and after a week of "fiendish physical torture" at No 1 Boot Camp in Ibiza.
Spencer definitely worked up a sweat, and after seven days, he now weighs in at 12 stone 6lbs - 8lbs lighter in less than a week.
His new lean figure and six-pack is a result of the Stairway of Doom - 181 steep steps built into the side of a cliff, which he had to run up and down 10 times with a dumbbell.
Describing the pain, Spencer said: "This was agonising muscle pain and a nauseating test of stamina."
Spencer also did lots of boxing, yoga and the burpee challenge, which is a type of exercise to tone up and boost core muscles and body strength to the max.
"I've got to say I found it easier in the mornings to get motivated and to get some energy by taking a couple of Forza Supplements' T5 super strength," he continued. "They also helped me combat hunger pangs in the afternoons."
Despite calling it "daily torture", Spencer said he now feels "so much better" about himself.
"I was too ashamed at first to show my 'before' picture," explained the reality star. "I don't mind showing it off now because it is next to the after picture!"
During the opening episode of the MIC's new series, viewers saw Spencer surprise co-star Alex Mytton by ordering green tea for lunch. Well, it certainly looks like he's keeping up his healthy eating regime!
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