This eating plan is considered a fad diet. Fad diets often promote quick weight loss that is unsustainable and may severely restrict what you eat. They may be harmful and generally do not have long-lasting health benefits. Talk to your healthcare provider before making any major changes to how you eat.
Other people have also claimed that following a sardine-only diet helped them lose weight and improve their health.
Could eating nothing but sardines help you lose weight? Here’s what experts say.
How Does the Sardine Diet Claim to Work?
In 2023, keto diet advocate Annette “Dr. Boz” Bosworth, MD, popularized the sardine diet, also known as the sardine challenge or sardine fast.
On her website, Dr. Bosworth calls the sardine challenge “a short-term dietary strategy designed to reset your metabolism by focusing on sardines as a nutrient-dense, low-carb food.” She suggests starting with eating as many sardines as you want for three days straight.
Bosworth recommends sardines in oil and sticking to water and black coffee on the sardine diet, according to a 2023 interview. She said you can add “carb-free hot sauce” or seasonings to the sardines if you don’t like how they taste.
Can the Sardine Diet Help You Lose Weight?
It’s likely possible to lose weight eating only sardines, says Bonnie Taub-Dix, RDN, creator of BetterThanDieting.com and author of Read It Before You Eat It.
“But, not because they’re magical,” she says. “It’s because you’re severely limiting calories and variety that would otherwise come from a bounty of other foods you could be eating.”
Meridan Zerner, RDN, a dietitian at the Cooper Clinic in Dallas, says eating a few cans of sardines a day would result in a daily net calorie intake of about 1,200 calories, which is considered a low-calorie diet. Sardines just provide fat and protein, which support a ketogenic diet.
“People can lose weight pretty quickly on a ketogenic diet, but suffer with the initial symptoms that come with it, such as nausea, low energy, bad breath, and diarrhea,” she says.
Single-food fad diets are also restrictive, unsustainable, and not healthy, as they usually lack key nutrients, Taub-Dix says.
Potential Risks of the Sardine Diet
A sardine-only diet would create a number of nutrient deficiencies, including in fiber, vitamin C, and many phytonutrients that come from fruits, vegetables, and whole grains, Taub-Dix says.
These nutrients are “critical for immune functions, energy production, and overall well-being,” says Lina Begdache, PhD, RDN, an associate professor of health and wellness studies at Binghamton University SUNY in New York.
Some canned sardines are high in salt, and eating too much could mean excess sodium, says Kaytee Hadley, RDN, a functional medicine dietitian and founder of Holistic Health and Wellness in Richmond, Virginia.
Regularly overdoing it on salt could raise your risk for high blood pressure and heart disease.
Sardines are also high in purines, a chemical found in fish and other foods that can raise your uric acid levels and increase your risk for gout, Hadley adds.
Following a strict high-protein diet without fiber could alter the gut microbiome, which could affect your gut health long term, Begdache says.
Overall, Zerner says, “This is a very restrictive plan that, over time, could be problematic.”
For instance, the monotony and rigidity of eating one thing could lead to binging on other foods, and it’s also likely not a sustainable way to eat, she adds.
Are Sardines Healthy in Moderation?
Sardines are “a nutritional powerhouse in moderate amounts,” says Begdache. “They are one of the best animal proteins you can eat.”
She says sardines are rich in many nutrients, including:
- Omega-3 fatty acids, which are good for your heart and brain and can also reduce inflammation
- High-quality protein, which supports muscle maintenance and feeling full
- Calcium, especially in canned sardines with bones, which supports bone density and your nervous system
- Vitamin D, which is important for bones and immunity
- Vitamin B12 and selenium, which are key for metabolism and thyroid function
“You don’t need to eat only sardines to get these benefits. But they can easily be part of a balanced diet,” says Hadley.
Sardines are also low in mercury compared with many other fish, she says.
Zerner recommends eating a 3-ounce serving of fatty fish, like sardines, twice a week. Pair the fish with vegetables and whole grains for a more balanced meal, Hadley adds.
Taub-Dix also suggests incorporating a variety of protein sources, such as other types of lean meat, tofu, or beans.
When purchasing sardines, Dr. Begdache suggests looking for low-sodium products (or rinsing the sardines to minimize salt) or choosing sardines packed in water, which tend to be lower in calories than those packed in oil.
Also, eat the bones and skin to get the most nutritional value, she says.
Is the Sardine Diet Right for You?
It’s important to talk to your doctor before trying a diet like this.
People with kidney disease, high blood pressure, or gout should be cautious about adding sardines to their diets, Taub-Dix says. Pregnant women should also limit their intake, Begdache says.
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