Carnivore diet sardine fast: I was not prepared for what this fad diet did to my body.
By: Luke Winkie (Slate Magazine)
Who are these people and why do they exist?
I don't often wander into the tinned fish section at my grocery store. Growing up, our family only kept a stock of canned tuna around for our three cats, who savored the banquet of preservative-drenched meat like dessert after a sad meal of chalky dry food. For me (and many other Americans), the idea that humans can find dinner behind an aluminum flap runs counter to the primary axiom of seafood—that it's best served fresh. So, I can't say I was excited to return home from the market last Monday with a stack of sardines tins, each marinating in a unique flavor like coconut curry, spicy marinara, or olive oil and black pepper. The lot of these teensy, decapitated fish were going to be my breakfast, lunch, and dinner for the next 24 hours, and according to the sardine fanatics around the world, my life would never be the same.
This stunt is called a "sardine fast." It's become one of the hot fad diets of the health internet in recent years, and the rules are absurdly simple. You eliminate all sources of nutrition from your table other than the saline tang of tinned sardines, served without bread, saltines, or any other accoutrements that might make the fish go down easier. Water, tea, and black coffee are to be your only beverages throughout the fast, and to complete the gauntlet, you supposedly need to do this for three whole days. The sardine fast was originally popularized in 2023 by Annette Bosworth, better known as Dr. Boz on YouTube, an internist and a strong proponent of the low-carb, high-protein ketosis diet. Bosworth sells beef liver capsules on her website, and she was also stripped of her medical license in 2015 after violating a bevy of election laws during an ill-fated run for Senate in South Dakota. With that in mind, it isn't shocking that Dr. Boz did not respond to my repeated interview requests.
Scandals aside, roughly 652,000 people have watched Bosworth's video detailing the benefits of a sardine fast. She asserts that the fish is high in omega-3s, vitamin E, and calcium, and when eaten en masse over a three-day span, they can "surge your ketones"—referring to a physical state called ketosis, where someone's body sources its energy from fat, rather than glucose, boosting weight loss. (Ketosis is where the low-sugar ketogenic diet gets its name from.) Bosworth uploaded that video last May, and since then, fitness bloggers, keto adherents, and curious civilians all over the world have experimented with a sardine plunge, to the point that social media is now littered with people puckering their faces in disgust as they struggle through a third or fourth helping of the reeking, lukewarm fish. Some of them endorse the process wholeheartedly. Others highlight the pitfalls that come with such a prohibitive palette. For instance, YouTuber Kendra Von Esh said, in no uncertain terms, that by the second day of eating exclusively sardines, she was stricken with "the runs."
Meanwhile, Courtney Luna, a vlogger and former chef who recently documented her week-long sardine fast on her channel, had to cut her 10-day sardine fast short by three days because her body was "saying I should stop." Still, she found it worthwhile. "There's just something magical about these fish," she told me. "They really helped me understand my hunger cues. It's easy to overeat bacon and steak because they're so delicious. But I don't love sardines, so I was truly eating because I was hungry."
Luna told me that all of the promises Bosworth made about her sardine fast came true. Her glucose dropped, her ketones spiked, and by the end of the seven-day period, Luna had shed six pounds. (She did not , however, develop a fondness for sardines.) Luna was especially prepared for such a drastic shift in her eating habits. She lives by the dictums of the "carnivore diet"—an extreme lifestyle endorsed by Jordan Peterson that asks its participants to exclusively consume animal products. Adherents of the diet claim that this can regulate blood pressure and stabilize mood swings, but as Healthline notes, "no controlled studies support [those] claims." Generally speaking, you should also be getting plant compounds in your diet, and Healthline further explains that an all-meat diet contains no fiber, which could lead to some terrible constipation, as well as osteoporosis, gout, and impaired kidney function.
Nevertheless, the sardine fast has become a fixture within the carnivore community, and medically speaking, they aren't wrong that the fish is strikingly beneficial to human biology. "The American Heart Association recommends consuming fish at least twice a week," Beth Czerwony, a dietician at the Cleveland Clinic, told me. She cited studies showing that a routine dose of oily sardines can improve cholesterol levels, regulate the digestive tract, and even decrease the chance of developing dementia. Czerwony was less eager to give her approval to a militant, all-day sardine binge, noting that the fish is notoriously high in mercury. But all things considered, there are certainly worse fad diets to test drive.
"The first two days, I didn't feel good. I was irritable. But on day three, I felt great. I didn't crave any other food," said Alex Monsen, an insurance agent in Utah, who is not a carnivore, but recently completed his own 72-hour sardine circuit. He learned to love the fish, and claims that sardines have assisted in everything from his energy levels to his joint pain.
"I'd recommend them to everyone," continued Monsen. "I try to convert people. I have a guy interested at work, because he sees me eating sardines regularly. He's always talking about how he wants more protein and I grab a tin and say, '22 grams of protein, no carbs, Vitamin B12. You're gonna feel good afterwards.' Everyone thinks I'm weird, but once they try it, they'll get it."
Personally, I was not prepared to sacrifice three whole days of my mortal existence on the altar of sardines, mainly because I hadn't yet discovered whether or not I even liked the fish. But 24 hours? That I could do. So, at 9 a.m., I peeled off the tin cover of my breakfast. I chose the cheapest, and most neutral brand in my cobbled-together sardine collection. The container encompassed six sardines, gutted, descaled, and luxuriating in a bath of olive oil. I wanted to gain a decent understanding of the fish's essential flavor profile, and I suspected that the numerous other marinades available mostly existed to smother the rankness—in the same way you feed a dog its medicine by embedding it in a mound of Purina. I retrieved a fork, but the filets slipped off its prongs, so I dug in with my fingers instead. Bottoms up!
It turns out I don't hate sardines. Thank god. It was not the most satisfying breakfast I've ever had, but I was able to get the fish down with relative ease, occasionally pausing to savor the unanticipated meatiness of each bite. The oiliness was intense, but not overwhelming, and I've endured far more putrid blasts of fishiness in other dishes. Suddenly, it made sense why America is in the midst of a millennial-driven tinned fish boom—according to Fortune, the industry's total sales jumped from $2.3 billion in 2018 to more than $2.7 billion in 2023. Much of this, I suspect, can be chalked up to the pleasingly nautical art-deco exteriors on the cans, which certainly play well on Instagram-ish picnic spreads. But the seafood inside isn't bad, either. Maybe those Europeans are onto something.
I sucked down another can a half-hour later, and reached a gastrointestinal cruising altitude shortly thereafter. My biggest fear about this fast was that I'd spend all day in a starved, ornery haze while all of my familiar carbs and sugars batted eyelashes at me from the kitchen. But that didn't happen. Instead, I slipped into a rhythm at work, free of hunger and fully satiated. Maybe this would be easy! Maybe I'm more than capable of pulling off a sudden nutritional pivot than I thought! Maybe I can choose to be healthy whenever I want!
The first tin of sardines I tried were pleasantly neutral. Luke Winkie
That is, of course, until lunchtime rolled around. That's when I flatlined. I live in New York City, which means I am always a half-block away from a bodega and its bounty of deliciously processed snacks. On most weekday mornings, I make a trip downstairs for a quick treat. Usually I'm on the hunt for something salty or sweet that's covered in artificial sour dust or a blast of traffic-cone-orange cheese. I would never consider this habit to be a dependency, because that feels like an insult to those in the throes of much heavier contraband. But it's hard to describe what happened to me in the afternoon of my sardine fast with language that doesn't evoke withdrawal. I suddenly grew lightheaded, groggy, and unable to focus. My stomach growled. My whole body felt askew. I wasn't hungry , exactly—the sardines amounted to a solid 400 calories or so—but I found myself desperate for a hit of carbs and sugar. The ketogenic community speaks of the "keto flu," a sense of sickness that settles in during the beginning of your purge, usually in the first day or two. I doubt I was in the full throes of the destabilization, but clearly, my body was beginning to reject something.
I cracked open two more cans of sardines—one packed with coconut curry, the other with a hot pepper kick—and I hoped the diversity of flavors would shock my body back towards equilibrium. It didn't work. I was still out of sorts. A few more hours went by, where I employed all of the tactics I've learned to defeat momentary spells of nausea or dizziness. I drank water. I took deep breaths. I slowly paced around the living room, until eventually, I gave up. A plastic bag of 99-cent corn chips was retrieved from my bodega. I stuffed a handful in my mouth, and the blast of carbs returned me to earth, like morphine hitting the bloodstream.
The coconut curry sardines that did not even kind of mitigate my bodily chaos. Luke Winkie
Afterwards, I was pretty much fine. The emergency corn chip maneuver was the perfect sin to break up a long day of sardines. I cracked open two more cans for dinner and went to bed hungry, but no longer unhinged. The next morning, my scale informed me that I was lighter than I've been in four years. Had I achieved the fabled ketosis? Probably not, but on my most recent trip to the grocery store, I did pull my cart back to that place it has rarely been—the everlasting mystery of the tinned fish aisle, which is still brimming with flavors I have yet to try. Maybe I am something of a convert. Perhaps there are many more sardine lunches in my future. Just don't be surprised if they're served with a pack of Skittles on the side.
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Ketosis won't solve the problem of overeating.