The sardine diet: brilliant fish, pointless diet.
A few days of sardines, eggs and olive oil to "reset" your body. The tin is one of the best foods in the supermarket. The reset is a social-media invention with no evidence at all.
The short version
- What it is
- A short challenge, usually three to seven days, eating mostly sardines plus eggs, olive oil and some vegetables.
- Good for
- Nothing the diet itself has proven. Sardines as a food: protein, omega-3, calcium, vitamin D, B12.
- Bad at
- Lasting. Variety. Your breath. Anyone with gout.
- Evidence
- None for the diet. Good for eating fish regularly.
- Our take
- Skip the challenge, keep the tin. Sardines go on your plan twice a week, for life.
What the sardine diet actually is
It's a trend, not a diet anyone designed or tested. The versions you see online vary, but the idea is the same: for a few days, you eat sardines at most meals, with eggs, olive oil and a bit of salad or vegetables. Some versions allow lemon, avocado and coffee. Some ban everything else. It's sold as a "reset", a quick fat-loss kick or a cure for bloating.
We looked for trials of this as a diet and found none. No randomised trial, no cohort study, nothing. What we did find is plenty of good evidence about eating fish, and sardines in particular. So let's split it: the food, yes; the gimmick, no.
How it works in your body
There's no special sardine mechanism. If the diet makes you lose weight in a few days, it's for the same reason any short, very restrictive plan does: you eat fewer calories and fewer carbs. Some of the first drop on the scale is water, not fat, and it comes back when you eat normally.
Meanwhile the sardines themselves deliver a lot. A 100 g portion of sardines tinned in oil, eaten with the soft bones, has about 25 g of protein, 382 mg of calcium, 4.8 µg of vitamin D, 8.9 µg of vitamin B12 and close to 1 g of the long-chain omega-3 fats EPA and DHA.1 For comparison, the EU reference intake for adults is 15 µg of vitamin D a day,2 4 µg of B123 and 950 mg of calcium.4 100 g covers your B12 for two days and about 40% of your calcium. That's a seriously useful food.
What you eat, what you don't
Eat (the sane version)
- Sardines, tinned or fresh, two or three times a week
- Other oily fish: mackerel, herring, salmon, anchovies
- Eggs, beans, chicken on the other days
- Plenty of vegetables and salad
- Olive oil, lemon, herbs
- Rye bread or wholegrain toast, sometimes
Forget it
- Days of sardines and nothing else
- Sardines in sugary tomato sauce as the default
- Very salty tins every day without checking labels
- "Detox" claims of any kind
- Repeating the challenge every month
Alcohol on the sardine diet
OK, now and then
- A glass of dry white wine or Vinho Verde with grilled sardines
- A small dry cider or a light beer
- Spirits with soda water and lemon
Not during a "reset"
- Drinking on a near-empty stomach after a day of tiny meals
- Beer by the jug at the sardine festival
- Sweet cocktails and mixers
- Heavy drinking if you have gout
50 Club: one small glass of dry white with a sardine dinner.
Alcohol is a known risk factor for gout,6 and the WHO says no safe level of drinking has been shown.9 All the details are in our alcohol guide.
What it's good for, with proof
Not the diet. The fish.
Low mercury, high benefit
Big predatory fish like swordfish and shark collect a lot of mercury. Small fish like sardines don't. The US FDA puts sardines, anchovies, herring and mackerel on its list of "best choices".5 A large review in JAMA weighed benefits against contaminants and concluded that for most adults, eating fish once or twice a week does far more good than harm.7
Nutrients that are often low
Vitamin D, calcium and B12 are worth watching, especially in northern winters or on plant-heavy diets. Tinned sardines with bones deliver all three in one cheap tin.1 That's why we like them so much in our Atlantic diet and anti-inflammatory food lists.
The uncomfortable truth
"A sardine reset melts fat in a week." There are no studies of the sardine diet. Not one. A few days of very restricted eating can shift the scale, but early losses are mostly water, and they come back. A diet with no evidence and an end date isn't a reset. It's a break from your normal habits, which are still waiting for you on day eight.
"The omega-3 in sardines is the magic." Omega-3 in capsule form has disappointed in large trials: a Cochrane review of 86 trials found little or no effect on deaths from any cause.8 The benefit of fish seems to come from the whole food, eaten regularly, replacing worse options. Not from a seven-day binge.
The risks
- Gout. Foods rich in purines, mostly from animal sources, are a known risk factor for gout.6 Sardines and anchovies are among the higher-purine fish. If you've ever had gout or kidney stones, a sardine-heavy week is a bad idea.
- Salt. Tinned sardines carry about 300 mg of sodium per 100 g.1 Several tins a day add up. Rinse them, or pick lower-salt brands.
- Too narrow. Days of the same food means missing fibre, vitamin C and many other nutrients. Short-term, not dangerous. As a habit, a problem.
- Pregnancy. The NHS says to keep oily fish, sardines included, to two portions a week when pregnant.10 A sardine week blows straight through that.
- Diet cycling. Monthly "resets" teach you that eating normally is the problem and punishment is the fix. It isn't.
Allergies: watch the staples
| Staple | Allergen (EU list of 14)11 | Swap |
|---|---|---|
| Sardines, anchovies, mackerel | Fish | Eggs, chicken, beans; walnuts, flax and chia for plant omega-3 |
| Eggs | Eggs | Beans, tofu, chicken |
| Rye or wholegrain toast | Cereals containing gluten | Potatoes, rice cakes, buckwheat |
| Sardines in mustard sauce | Mustard | Sardines in olive oil or water |
| Some tinned fish in sauces | Celery, sulphites (check label) | Plain tins: olive oil, water, lemon |
Don't do the sardine diet if you…
- have gout or have had kidney stones
- are pregnant or breastfeeding
- have been told to restrict salt
- have a fish allergy (obviously)
- have ever had an eating disorder: "resets" and challenges are a classic trigger
Healthen me asks about all of these and gives you a different plan if any apply.
How we use the sardine diet in your plan
We don't use the diet. It's an information article, because there's no evidence for it and a one-food challenge doesn't fit a plan for life.
We do use sardines, a lot. They're one of our favourite foods for breaking a fast: protein, healthy fat, almost no carbs, and they keep you full. Sardines on greens with olive oil and lemon, or on a slice of rye in the 50 Club. They count towards your two-a-week fish target, and if you're pescatarian they're one of your best friends.
Cheap, long-life, no cooking. Keep a few tins in the cupboard. That's the real sardine diet.
This article is general information, not medical advice. If you have a medical condition or take medication, talk to your doctor before changing how you eat.
Sources
- US Department of Agriculture, FoodData Central. Fish, sardine, Atlantic, canned in oil, drained solids with bone (FDC ID 175139). fdc.nal.usda.gov/fdc-app.html#/food-details/175139/nutrients
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Dietary reference values for vitamin D. EFSA Journal 2016;14(10):4547. doi.org/10.2903/j.efsa.2016.4547
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on dietary reference values for cobalamin (vitamin B12). EFSA Journal 2015;13(7):4150. doi.org/10.2903/j.efsa.2015.4150
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on dietary reference values for calcium. EFSA Journal 2015;13(5):4101. doi.org/10.2903/j.efsa.2015.4101
- US Food and Drug Administration. Advice about eating fish (revised October 2021). fda.gov/food/consumers/advice-about-eating-fish
- National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIH). Gout: symptoms, causes and risk factors. niams.nih.gov/health-topics/gout
- Mozaffarian D, Rimm EB. Fish intake, contaminants, and human health: evaluating the risks and the benefits. JAMA 2006;296(15):1885–1899. doi.org/10.1001/jama.296.15.1885
- Abdelhamid AS et al. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews 2020;3:CD003177. doi.org/10.1002/14651858.CD003177.pub5
- WHO Regional Office for Europe. No level of alcohol consumption is safe for our health. News release, 4 January 2023. who.int/europe/news/item/04-01-2023-no-level-of-alcohol-consumption-is-safe-for-our-health
- NHS. Foods to avoid in pregnancy. nhs.uk/pregnancy/keeping-well/foods-to-avoid
- Regulation (EU) No 1169/2011 on food information to consumers, Annex II (the 14 allergens). eur-lex.europa.eu/eli/reg/2011/1169/oj