Justin Bieber has engaged in a war of words with a doctor after the NHS personnel challenged his Instagram post which claimed: "The right healthy food is actually medicine."

The feud started when Dr. Joshua Wolrich, an NHS surgical doctor who also hosts a podcast titled "Cut Through Nutrition," tried to correct Justin Bieber when the pop-star stated in a post on Sunday: "If you are feeling anxious or depressed it can often have a lot to do with our diet!"

The musician, who himself has had a lengthy battle with his mental health, added in the caption: "Try changing up your diet! It has helped me so much !!!" Dr. Joshua dropped a comment on the post to warn the "Baby" hitmaker that the message he is sharing has the potential of actually being quite harmful.

He commented: "The intention behind this post is good, but unfortunately the potential outcome is quite harmful. Food is many, many things but it's not medicine. That's not to say it isn't important – it provides us with nutrition and energy to thrive, but it has its limitations."

The medical professional added that anxiety and depression are very rarely a result of food intake. Calling the mental health "complex," Dr Joshua told the musician that "boiling it down to the privilege of food choices is incorrect and stigmatising for those who struggle with it on a daily basis."

"For any of you who read this and felt a sense of guilt that if only you changed your food you wouldn't struggle with mental health...please know that's not accurate. You are doing a fantastic job - do not compare yourself to a celebrity with all the capacity for change and privilege in the world," he concluded.

However, the comment did not go down well with the "Yummy" singer, who took to Instagram stories to hit back at his critic. Posting a screenshot of the doctor's comment, the 26-year-old wrote: "Bro literally f*** off lol."

Dr. Wolrich, whose Instagram bio says he is "fighting weight stigma," and feed is also full of posts about the issue, responded to Bieber's story by posting a video message about "food is medicine" idea.

"Food is food. Medicine is medicine. We need to respect both but not conflate the two. Let's find better ways of expressing just how important food can be," he captioned a video of himself in which he spoke about how food is not capable of curing cancer and requested people to use the phrase "food is medicine" in a better manner.

He wrote another detailed post about the issue, alongside a picture that repeated that "Food cannot cure cancer," and concluded with "It cannot prevent it either." Joshua explained in the caption: "There is a huge difference between something having the ability to reduce risk of disease vs. prevent or cure it."

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Justin Bieber Kevin Winter/Getty Images

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Justin Bieber NHS