Karen Foreman-Brown ate very few carbs for nearly a year. She and her husband, who were following the keto diet, filled their bellies with fat- and protein-rich items like brisket and brie, and their shopping carts with non-starchy vegetables like cauliflower and kale. They didn't consume cupcakes at parties, corn cobs at fairs or Coronas at pubs. And, contrary to what most health experts might expect, they weren't exhausted. In fact, they wanted more.

"My energy levels were good; I felt great, but I had stalled a bit on the weight-loss front," says Foreman-Brown, a 54-year-old digital marketer in Nelson, New Zealand, who'd lost about 30 kilograms (or 66 pounds) on keto in 2017.

So she and her husband decided to take it a step further and try the carnivore diet, an eating regimen that includes only animal products, mostly – if not entirely – red meat. No plant foods, including non-starchy vegetables, nuts and seeds, are allowed. One theory is that since ancient humans presumably lived entirely off the buffalo and woolly mammoths they killed, humans are designed to be nourished by animals only. Many followers also believe that plants are toxic to human health, in part because they contain mechanisms to fend off bugs and other animals. Eating only animal products, proponents claim, can lead to a host of positive health outcomes, from weight loss to addiction recovery to joint pain relief to sexual prowess.

"I thought it was worth a try to further optimize my health," says Foreman-Brown, who'd heard about the diet in late 2017 through podcasts and Facebook groups devoted to the keto lifestyle. If after a month she didn't like it or feel better, she'd return to keto. That didn't happen.

Instead, Foreman-Brown lost 11 more pounds during the first couple weeks and has maintained a stable weight since. Now, about a year later, she and her husband remain "carnivores," typically eating two meals a day – perhaps steak and fried eggs at breakfast, chicken skin chips for a snack and another steak or two (each) for dinner. Some carnivores, including Foreman-Brown on occasion, also eat fish and some dairy products, but no sides, sauces – or, Foreman-Brown says – hassle.

"One of the biggest benefits is how simple it is to eat this way," Foreman-Brown says. She and her husband don't waste vegetables that have gone bad, enjoy more kitchen space (so long, blenders and measuring cups and vegetable slicers) and avoid decision fatigue at restaurants. They'll have the steak, period. "We just have to explain to the waitstaff that we don't want any sides or plants," she says. They've gotten to know their local butcher and stay within their budget by taking advantage of specials.

Foreman-Brown and her husband are part of an increasingly robust (online, at least) community of carnivores whose meat-only diets fly in the face of all conventional wisdom and decades of dietary research that supports varied, plant-based diets for disease prevention and longevity. Where health professionals say fruits and vegetables are hallmarks of health, carnivores say they're toxic. Where nutrition guidance links excess red meat consumption to heart disease and cancer risk, carnivores credit eating multiple ribeyes a day for their stellar cholesterol and superhuman endurance. Where dietitians advise moderation, carnivores revel in elimination.

The eating regimen is making headlines because "the more extreme (the diet), the more sexy and compelling," finds Brian St. Pierre, a registered dietitian in Scarborough, Maine, and director of performance nutrition at Precision Nutrition. "It feels very rebellious and anti-establishment."

But carnivores aren't as rare a breed as one might imagine. The Carnivore/Keto Diet Facebook group, for instance, has about 20,000 members who are presumably following – or interested in following – one of the plans. The Women Carnivore Tribe group has more than 8,000 members, including Foreman-Brown. Google searches for "the carnivore diet" peaked in summer 2018 after being near nonexistent in years' prior. And the website Meat Heals has published hundreds of first-person accounts of the positive health outcomes achieved – from diabetes reversal to eating disorder recovery – experienced after switching to an exclusively animal-product diet, often from a vegan pattern.

"You can't ignore all of this or say they're lying or genetic freaks," says Shawn Baker, an orthopedic surgeon by training who's behind the Meat Heals site and authored the 2018 book, "The Carnivore Diet." He's followed the plan for several years – and, he believes, achieved optimal health and broken world rowing records in middle age because of it. Baker surrendered his medical license in 2017 after the New Mexico Medical Board found him "incompetent to practice" along with another allegation, but Baker stands by his performance and says he expects he'll have a medical license again soon. "Maybe there's some things we don't know" about what's really good for human health, Baker adds. "That's the whole point of the diet."

While there's no research (yet) on the carnivore diet, some health experts are willing to find upsides for some people. For one, St. Pierre, who's not an advocate for the diet but willing to throw it some bones, reasons it is short on rules: eat meat, drink water, eat when hungry, stop when full. It's also reasonable that it would lead to weight loss since followers are likely slashing calories. Meat is filling, slow to digest and can get old fast. There's even a nutritional principle describing that the less varied your food choices are, the less you want to eat, St. Pierre says. (The opposite of that is "the dessert effect" – you feel full, but once dessert comes along, you find room. If your only dessert option is another steak, you don't.)

The diet can also make people feel better in the short term if they're accustomed to a diet high in processed foods and sugar, says Robin Foroutan, a registered dietitian nutritionist in New York City who specializes in integrative medicine and serves as a spokesperson for the Academy of Nutrition and Dietetics. Plus, going carnivore is certainly one way – albeit an extreme one – for people to eliminate foods they didn't know they were sensitive too. "Now that they've pared down their diet, they're not getting those foods anymore, so it's possible they feel better in the short term," Foroutan says.

But such potential perks don't hold a candle to what health experts have long known is critical for the vast majority of people when it comes to chronic disease prevention, longevity, environmental sustainability and, frankly, sanity: a flexible diet rich in fruit and vegetables; nuts, seeds and legumes, seafood and lean meat and whole grains. A panel of 23 esteemed doctors, nutritionists and weight-loss specialists, for instance, considered the keto diet – the closest to the carnivore diet – among the worst of 41 diets overall in U.S. News' annual rankings, and plant-based diets like the Mediterranean at the top.

They and other health professionals cite research like a 2017 study of nearly 19,000 Italians finding that the more closely people followed a Mediterranean diet, the lower their risk of heart disease. Or, this review of reviews concluding that "red meat and processed meat convincingly increases colorectal cancer risk by 20 to 30 percent." Plus, research on the so-called "blue zones," or parts of the world where people are most likely to live beyond 100, finds that one of the traits they have in common is a diet rich in beans and scarce in meat. Baker and other carnivores contend that such studies don't mean much in part because they're population-based associations – not cause-and-effect proof – involving small amounts of meat, on average.

There's also concern in the medical community about what might happen, especially long term, without most vitamins, minerals, fiber and other anti-inflammatory compounds found in plants. "To cut out vegetables and herbs and spices, you're taking out all antioxidants and phytochemicals," Foroutan says. "You're not getting very many vitamins and not a lot of omega-3 fatty acids," she adds. "There's nothing coming from the diet to help manage inflammation."

Foroutan also points out that a diet void of plant foods can negatively affect the composition of gut bacteria as well as tilt the body's acid-alkaline balance toward potentially dangerous levels of acidity. "If the diet is very acid-forming and the body has to work to buffer the effects of that to keep the blood neutral, those other cells (like brain cells) tend to suffer," she says.

Even the carnivore-centric program and website Meat Health cautions followers about the inevitable "trough of despair," or the "adjustment" period the body experiences when switching to a carnivorous pattern. For some people, it's so bad they experience "a certainty (they) are going to die," due to side effects including brain fog, headache, chills, sore throat, digestive issues, dizziness, irritability, bad breath, dry mouth, muscle soreness, nausea, diarrhea, rapid heart rate, insomnia, night sweats and decreased performance, energy and drive, the site reports.