I won’t share my husband’s precise reaction when I told him I was embarking on a “sardine fast,” just know that it wasn’t positive. As someone with a major proclivity for tinned fish—anchovies, sprats, mackerel, you name it—the prospect of eating nothing but sardines for three days, as per the internet’s instructions, didn’t feel especially daunting to me. But I did pity anyone who might encounter me during this time, and as my significant other, he was directly in the firing (or should that be fishing?) line.
The viral dietary trend of the moment, the sardine fast, is currently racking up thousands of views on TikTok. Google reports that searches for both “sardines” and “Dr. Boz sardine fast” have risen by over 5,000% in recent months. So what’s going on? Why so much fuss over such a small and unassuming fish?
What is a sardine fast?
Lasting between one and three days (or more, if you fancy it), a sardine fast simply involves eating tinned sardines… and nothing else. The idea is that it can lower blood sugar, promote rapid fat loss (thanks to supposedly increasing ketone levels), and—most importantly—give you glowing skin. It was the latter side-effect that persuaded me to give it a shot.
This most specific of fasts has gained traction in recent months for two reasons. Dr. Annette Bosworth (also known as “Dr. Boz”), an American physician who specialises in metabolic health, has promoted it as a quick way to raise ketones on TikTok and in podcast appearances. Meanwhile, Dr. Dominic D’Agostino, a researcher in metabolic therapy, in conversation with biohacker Tim Ferriss, claimed his friend, “Dr Squat” went into remission from metastatic prostate cancer after week-long sardine fasts once a month.
While they are all convincing orators, I prefer to tread with caution when it comes to viral wellness trends. It also made me wonder if whether it was really beneficial for anyone to limit their diet to solely fish. The only way to really understand? By trying it myself.
Day 1 of my sardine fast
It’s a dangerous day to be a sardine: I am ready and raring to go with a selection of sardines in olive oil, spring water, and tomato sauce. I open a tin, place the contents in a small bowl and heat them up. I’ve seen some people eat them cold, but since I am not an actual cat, that’s a step too far for me.
It’s breakfast time and I love fish in the morning—often eat mackerel or herring first thing. They’re a great source of protein and rich in omega-3s, particularly EPA and DHA, which nutritionist Dr. Federica Amati tells me act like the body’s natural anti-inflammatories. “They support heart health, help balance cholesterol, and play an important role in brain function, mood, and the appearance of our skin,” she explains. “Add to that high-quality protein, vitamin D, B vitamins, calcium (especially when you eat the soft bones), selenium, and other trace minerals. They’re a complete package.”
They also taste good, and keep me satiated until at least midday, when I begin to ponder my next meal. Spoiler alert: it’s more fish.
I’m already starting to dread it a bit, honestly. Where are the vegetables? And I’d really like some carbs. Instead, I eat my sardines and stay super hydrated with ginger tea and water laced with electrolytes (I am not good at fasting).
Come evening, I’m cranky, low on energy and ravenous. I treat myself to sardines in tomato sauce—a nice departure from olive oil—sprinkle some salt on top, and soldier on. It’s hard to eat sardines while your husband is enjoying a delicious pho, but rules are rules.
Do I notice better skin or energy? No. I just feel tired.
Day 2 of my sardine fast
Another day, another tin of sardines. I begin as I did yesterday, while reminding myself that sardines are good for me. Lower cardiovascular risk, steadier metabolic health, and reduced inflammation are all realistic benefits of eating oily fish regularly, says Dr. Amati. “There is so much goodness in this little tin. I just need to remember it,” I write in my gratitude list, thoroughly unconvinced.
To get through the day, I chase my sardines with miso soup to boost satiety. By dinner, I’m low on energy and slightly grouchy. Nothing another tin won’t fix! I have a bath and go to bed, hoping the omegas are doing good things to my skin, which is actually looking quite good, if I do say so myself.
Day 3 of my sardine fast
As my recycling bin fills with tins, my optimism rises, too. Day three! I can do this!
I feel sick at the thought of more sardines, but I persist because—actually?—I don’t look too bad today. My skin is pretty glowy and clear. Still, I’m unconvinced it’s solely down to the fish. The past few days have seen me cut out bread and sugar, drastically increase my fluids (miso, water, herbal tea), and generally behave myself. I’d wager it’s more to do with this combination than the sardines alone.
“Mono diets, where you eat just one food for several days, aren’t supported by evidence,” Dr. Amati agrees. “We need diversity for our gut microbiome, nutrient intake, and overall resilience. Eating only sardines risks nutritional gaps, excess salt and unnecessary stress on the body. There’s also no credible research suggesting it will transform your skin. Quick fixes are seductive, but biology doesn’t really work that way.”
I nearly make it through the day. For dinner, I (whisper it) have my all-time favorite: anchovies on buttery toast. Still fishy, but an appropriate Friday reward after eating like a seal for most of the working week.
Sardine fasts: a conclusion
Well, I won’t be doing that again. I’m a huge fan of sardines as part of a varied diet, but eating them exclusively is an experience I have no desire to repeat. While, yes, I feel lighter and my skin looks glowy, this kind of approach feels more like a crash diet than anything truly beneficial for health or complexion.
To my mind, healthy skin is about variety: good-quality protein, healthy fats and plenty of fibre, all paired with colourful, antioxidant-rich plants—and Dr. Amati agrees.
So while it wasn’t quite as bad as my husband had feared, it’s not something I’ll be repeating. That said, given that they’re both nutritious and cheap, sardines are a superfood I’ll continue to add to my meals… just not three times a day.
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