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A new study from Harvard tested a controversial meat-centric diet, and come up with some surprising results.

The study, released via the Oxford University Press’ Current Developments in Nutrition journal last week, was led by Boston Children’s Hospital doctors Belinda Lennerz and David Ludwig, who also serves as a professor at the Harvard Medical School.

Based on data collected from 2,029 subjects who have been eating a so-called “carnivore diet” for at least six months at the outset of the study, the new paper is one of the first pieces of research in recent years to formally investigate the feasibility and health impacts of a diet based almost entirely on animal-based foods.

While the ketogenic diet, a very low carbohydrate, high fat diet has gained mainstream attention over the past decade, the carnivore diet, sometimes viewed as a more extreme version of the keto diet, has yet to be comprehensively researched by nutritionists.

Practitioners of the carnivore diet generally avoid plant-based foods, including not only refined grains and vegetable oils but also most fruits and vegetables, instead living primarily off of meat, eggs, fish, and in some cases, dairy.

The carnivore diet has drawn scorn from mainstream nutritionists, though a small but growing community of self-described ‘carnivores’ have claimed the diet in fact has offered them health benefits.

While tribal populations have been reported to subsist off of diets made up most of animal-based foods, the first modern medical report of an exclusively animal-based diet came in 1928, when American anthropologist Vilhjalmur Stefansson and a companion were placed under observation at Bellevue Hospital, as they remained on a meat-only diet for an entire year, inspired by Stefansson’s experiences with the Inuit in Canada, whom Stefansson claimed lived almost exclusively on fish and meat.

More recently, the diet was popularized by Canadian psychologist Jordan Peterson and his daughter, podcaster Mikhaila, after the two publicly discussed their use of the diet to treat long-running autoimmune disorders.

It was not until the Harvard study that the diet was subjected to systematic research.

The study found that, “contrary to common expectations”, “consuming a carnivore diet experienced few adverse effects and instead reported health benefits and high satisfaction. Cardiovascular risk factors were variably affected.”

Few participants (5.5% for the most prevalent reaction, gastrointestinal problems) reported adverse reactions to the diet, while most (95%) reported high levels of satisfaction and improvements in overall health.

Low-density-lipoprotein (LDL) cholesterol levels tended to be elevated among participants, but high-density-lipoproteins (HDL) and triglyceride levels were optimal. Overall, 56% saw improvements in their lipid panels, with 18% seeing no change, and 19% seeing a worsening of their lipid panels.

Participants with diabetes reported significant weight loss and reduction in their reliance on diabetes medication.

Among subjects who reported being overweight or obese, 93% saw their weight problem improve (41%) or completely resolve (52%) on the diet.

A similar percentage (93%) said the diet improved (32%) or resolved (61%) their hypertension, while 98% of those with diabetes said the diet improved (24%) or resolved (74%) their condition.

Large majorities of participants suffering from psychiatric, cardiovascular, and gastrointestinal ailments also said they improved or resolved their conditions on the diet.

However, the study relied upon a non-randomized sample of self-reporting participants, leading the authors themselves to caution that further study is required.

“The generalizability of these findings and the long-term effects of this dietary pattern require further study.”

Subjects were followed for between nine to 20 months (14 months on average), leaving questions of long-term effects unanswered by the study.

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