A gruelling diet and exercise regime undertaken by a 30 year-old man saw him lose a third of a stone in a matter of days.

In a YouTube video entitled ‘world’s most extreme diet’ that has amassed more than 2.5 million views, Will Tennyson, a Canadian based fitness influencer, undertook the challenge of only eating 1000 calories a day for four days.

The content creator embarked on the extreme ‘depletion’ diet, which saw him eat virtually small portions of chicken, green vegetables and no carbohydrates, forcing the body to rely more on fat which aids weight loss.

The strict rules also included walking 12,000 steps a day, drinking 7.5 litres of water, no artificial sweeteners and no seasonings.

Starting the journey at 12st 7lbs, he said: ‘It’s time to torture every last ounce of fat off my body.’

But the ordeal had a torturous effect on his body, resulting in a serious depletion in the male sex hormone testosterone, as well as debilitating symptoms like muscle weakness, extreme fatigue and even vision problems.

Tennyson’s personal trainer described the regime as ‘brutal’.

‘Hunger is through the roof. On day one he’ll start the day not feeling too bad, but by mid-afternoon he’s going to be dragging pretty badly.’

In a YouTube video that has amassed more than 2.5 million views, Will Tennyson, a Canadian based fitness influencer, undertook the challenge of only eating 1000 calories a day for four days. Pictured: before and after

As a bodybuilder, Tennyson’s success hinges on being as low fat as possible to allow every muscle to be extremely defined when posing on stage.

His trainer explained the purpose of the diet was to ‘flatten’ his body to help him achieve a leaner, more defined physique by reducing body fat and revealing more muscle definition.

He said: ‘He’s probably going to be dropping a lot of weight as the day goes on, this is going to lead to lower energy and he’s going to flatten out pretty quickly.’

But Mr Tennyson was already struggling with the extremely controlled food allowance before the end of the first day.

He said: ‘The last thing I need right now is more broccoli. I just need emotional support. I did not think that I’d get sick of this on day one. 

‘You know when you’re in middle-school and your friend moves away and you just miss them dearly? That is carbs for me right now.

‘It’s also pretty amazing that after I eat the meal it feels like I haven’t eaten and I’m actually hungrier.’

But by day three, and at 174.8 lbs, it was really taking a toll on his body, his legs were weak and he had very little energy to perform even basic tasks

He started to suffering from physical affects that made him ‘want to cry’

By the end of the day, he started to suffer from physical affects that made him ‘want to cry’.

‘I’m starving right now, my head is hurting, I kind of want to cry. If I wake up in the middle of the night I’m doomed.

‘Hunger induced insomnia is a cruel and unrelenting mistress.’

He showed viewers that he’d already lost three pounds in the first day.

But by morning, he was struggling.

‘I feel really weird right now, my head is pounding, like my brain is in a sensory deprivation tank and the water is slowly turning into sludge. I have absolutely zero ability to think.

‘I feel like a string bean, I have no vascularity. The only positive thing about this is that eating the same thing everyday makes things easy.’

By day three his legs were weak and he had very little energy to perform even basic tasks.

He said: ‘I’m never going to take food for granted again. I’m really feeling it now—my head, my legs are heavy, literally everything that doesn’t involve sitting and staring feels very overwhelming.

‘I am so down bad right now. Usually when it hits 4pm I become a completely different person and I feel like my body is shutting down. Blinking feels like cardio. 

‘I had to close the blinds because the sun hurts my head, I can’t watch TV because it hurts my head. I feel like if I stand up I’m going to fall over. and I’m also extremely moody. Everything just feels so overwhelming, my vision is kind of messed up too.’

Yet, the fat-busting effects of the diet were starting to show.

 ‘That’s the leanest I’ve ever been in my entire life, it’s absolutely crazy. I’m super happy with the look.’ 

His diet consisted of only eating small portions of chicken breast, olive oil, green vegetables and protein powder so that he could drop to five per cent body fat

Towards the end of the experiment he revealed blood test results showing his testosterone levels had ‘tanked’. 

This is likely because a deficiency in key nutrients like zinc, magnesium, vitamin D, and other beneficial compounds can impair the hypothalamic-pituitary-gonadal, which regulates testosterone production.

On the final day of the experiment the body builder powered through his last meals of bland chicken and green beans, desperate for carbohydrates.

Mr Tennyson measured his body fat at the gym and was delighted to reach his goal of only five per cent fat—nearly 20 per cent less than the average British male.

Of his day four appearance he said: ‘I look flat as hell. I’ve got no veins, it’s the worst I’ve looked during this depletion, but surprisingly it’s the best I feel. 

‘I think my body has wiped out all of the carbs from the days before depletion so I think I’m running on fat.

He added: ‘I think about eating so much food that I need to lie down and elevate my feet just from a complete binge, but then another part of me thinks I actually might miss this diet that I’m doing. It’s so routine for me that I think I’m going to be a bit sad when it’s all over.’

By day five he weighed 12st 4lbs, making a total weight loss of 4.5 llbs.

Concluding the crash diet he said: ‘Looking at the before and after, I definitely see a huge difference, especially in my quads, they sharpened up a lot. I do look a lot flatter and not as full.

‘Even just flexing in the after footage hurt, my muscles are actually aching I can’t connect with them at all so I’m hoping I soak up the carbs like a sponge.’