A Harvard medical student recently went vegan as a health experiment — and the results were surprising.

Plant-based diets have been heralded for their health benefits — but Nick Norwitz, 25, discovered that his LDL cholesterol actually spiked during his week-long food swap.

Low-density lipoprotein (LDL), sometimes called "bad cholesterol," is associated with negative health effects when present in high amounts, doctos say.

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After a week of eating an "almost entirely carnivore" diet, Norwitz switched to a "full vegan keto diet" for the entire following week. (See the video at the top of this article.)

His plant-based diet focused on tofu with some added vegan protein powder, green vegetables like spinach and Brussels sprouts, and some dark chocolate and macadamia nut butter, he said in his video.

For his primary fat sources, Norwitz incorporated macadamia oil, extra virgin olive oil and some toasted sesame oil.

In his video, Norwitz breaks down the specific amounts of macronutrients he consumed with the carnivore and vegan diets.

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"Honestly, my stomach got pretty upset on the vegan diet," Norwitz says. "That’s just me, and my biology and microbiome."

"Despite eating less total fat, less saturated fat, more fiber and zero cholesterol on the vegan diet, my total LDL cholesterol actually went up."

The reason for the LDL cholesterol spike on the vegan keto diet as compared to the "carnivore-esque" keto diet was calories, Norwitz said.

On the carnivore-like keto diet, he consumed 3,479 calories per day — "which is around maintenance for me, and my weight didn’t change."

On the vegan keto diet, he consumed significantly fewer calories — 2,054 per day.

"While I don’t adhere to the theory that calories cause obesity, that doesn’t mean calories don’t matter," he said — noting that the "acute dramatic drop in calories" triggered some weight loss.

Norwitz lost 4.2 pounds on the vegan diet, which he cites as the reason for the LDL spike.

Earlier published research has shown an "inverse association" between LDL cholesterol and body mass index on low-carb diets, he noted.

"Analyses have shown that leaner populations with BMIs less than 25 see increases in LDL," he said. "The leaner the person is, the higher their LDL goes up, all things being equal."

Norwitz goes into detail in his video about the scientific reasons for this association between lower BMI and higher LDL cholesterol.

He believes that these results would likely apply to other lean, active people on low-carb diets in a controlled setting.

Norwitz — a self-described "academician" with a PhD in metabolic health, who is currently finishing his medical degree at Harvard — said he has always had a passion for sharing his "joy and interest" in science.

"While humans can do just fine on plant-based diets, eating plant-based is not essential for health," Norwitz told Fox News Digital. 

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"My vegan-keto study, while certainly a carefully engineered metabolic demonstration, provocatively pokes at conventional ideas to, hopefully, force people to think more deeply about how each individual’s unique metabolic circumstances deserve individualized consideration," he went on. 

"In this way, it’s a radical demonstration trying to make a reasonable point."

Above all, Norwitz said he hopes his experiments inspire people to become more curious about their own metabolic health.

"Psychology is more infectious than the flu," he said. "I want people to vaccinate themselves with curiosity."

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Dr. Bradley Serwer, a cardiologist and chief medical officer at VitalSolution, an Ohio company that offers cardiovascular and anesthesiology services to hospitals nationwide, was not involved in the experiment but offered his input on the findings.

It's "impossible to extrapolate the experience" of one person across populations, Serwer told Fox News Digital.

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Just because something is labeled vegan doesn't make it healthy, the cardiologist cautioned. 

"It’s important to stay away from highly processed foods and refined carbohydrates (sugar), which are common in many vegan items," Serwer said.

Genetics also play a large role in a person's metabolism of cholesterol, he noted.

"Changing diets suddenly can disrupt your body's physiology and cause fluctuations in cholesterol levels," Serwer said.

For those choosing to go vegan, the doctor said, it's important to "increase soluble fiber, focus on whole foods, which are minimally processed, and incorporate healthy fats such as avocado, nuts, seeds and olive oil into your diet."