Although the sardine-summer fad has faded, one researcher didn’t let that stop him. He dove in “full dolphin,” as he put it — eating 1,000 of the tinned fish in 30 days.
Nick Norwitz, M.D., Ph.D., a Harvard- and Oxford-trained metabolic health researcher and educator based in Boston, set out to test whether an extreme sardine-only diet could mimic fasting and provide benefits such as fat loss and longevity without sacrificing muscle.
“Sardines — skin, bone and all — they’re nature’s protein bar and multivitamin in one,” Norwitz said in a YouTube video earlier this month following 30 days of the diet. He compared the fish to “a metabolic Swiss Army knife.”
For a month in October, the 30-year-old ate roughly three tins a day — about three to five fish per tin — and tracked weight, ketones, omega-3 levels and workout performance.
“I wanted to see if they could deliver the benefits of fasting without the drawbacks,” he said in the video.
Norwitz started with just sardines, then added olive oil and MCT oil — a fast-burning fat made from coconut or palm oil often used to boost focus and metabolism — to counter initial feelings of low energy.
He also added salt for electrolytes to maintain hydration and replace sodium lost during ketosis, when the body burns fat for energy instead of carbs.
“Honestly, adding that fat made a world of difference,” he reported in the midst of the experiment. “It’s been four days since I started adding that olive oil to my diet, and I just feel like night and day more energetic.”
Throughout the diet, Norwitz said he felt unusually “light” and “strong.”
He reported “boundless” stamina, breezing through workouts, practicing inversions on monkey bars and climbing the 37 flights of stairs to his apartment.
By the final week, he’d lost six pounds and reached what he called “dolphin-like” omega-3 levels. His blood test results showed omega-3 readings so high that they “broke the scale.”
“My blood looked more dolphin than human,” he joked.
Overall, Norwitz found that, in his personal experience, the sardine diet delivered high-quality protein, omega-3s and nutrients such as creatine and CoQ10 that boosted energy, burned fat and still preserved muscle. It also triggered ketosis and the metabolism-boosting hormone FGF-21, leading to weight loss and sharper focus, he said.
The main downside, Norwitz said, was that he began to smell “like a fish market,” despite showering, brushing his teeth and spritzing cologne. Just a few days in, his girlfriend told him, “You smell like you’re sweating fish.”
He tracked “kiss frequency” from her before and after sardine meals.
“I tracked kisses as data points,” he said. “So, in a blinded fashion, at least blinded to her, I tracked kiss frequency with an emphasis on the window four hours after I had a meal of sardines. And yes, I did brush [my teeth and] put on cologne. And honestly, I stopped tracking for five days because, true to her word, that number plummeted to zero. … That was a big downside.”
Despite that, he stuck with the diet — occasionally swapping in a non-sardine dinner with friends, usually seafood-heavy and low-carb, to keep his metabolism consistent.
Norwitz said the sardine fast “might be worth experimenting with” for people curious about fasting or metabolic resets, but stressed it’s not for everyone, especially those who are already very lean or sensitive to carb restriction.
He noted that extremely high omega-3 levels haven’t been extensively studied in humans.
“If I had to eat only one food, it would be sardines,” he told Fox News Digital. “When eaten whole, they’re nearly complete nutrition: bioavailable protein, quality omega-3 and loads of micronutrients. They’re also among the lowest mercury fish. You’d need to eat 77 servings of sardines to equal the mercury in one serving of swordfish.”
The National Heart, Lung and Blood Institute notes that the effects of omega-3s are nuanced and depend on the specific type, dose and individual health factors. Research is ongoing to determine who benefits most and why.
A 2011 review in the British Journal of Nutrition found that while long-chain omega-3s are generally beneficial, excessive intake can carry risks, including exposure to contaminants, oxidation of fish oils and increased bleeding risk — prompting researchers to caution that more is not always better.
Others have tried shorter sardine-only runs as part of keto-style fasts or metabolic resets, aiming to boost ketones, control appetite or speed weight loss.
Online accounts claim brief sardine streaks increase satiety and simplify dieting.
“The only thing preventing me from eating them daily now is I’d end up single,” Norwitz said.
Before starting a food experiment, one should always consult a doctor or nutritionist.
