The Sirtfood diet: a great shopping list wrapped in a very shaky theory.
Kale, buckwheat, walnuts, berries, olive oil, dark chocolate. Hard to argue with. The claim that they flip a “skinny gene” is another story, and the first week is mostly just a crash diet in a green glass.
The short version
- What it is
- A week of very low calories built on green juices and "sirtfoods", then a diet rich in those foods to "activate sirtuins".
- Good for
- Getting more plants, olive oil, nuts and berries into your week.
- Bad at
- Proving its own theory. The fast early loss is mostly water.
- Evidence
- Weak. No independent trials of the diet itself.
- Our take
- Keep the shopping list, bin the juice week and the red-wine permission slip.
What the Sirtfood diet actually is
Two British nutritionists published The Sirtfood Diet in 2016, and it went big when celebrities were linked to it.1 The idea: certain plant compounds activate sirtuins, a family of proteins involved in how cells handle stress and energy. Activate them, the book says, and you burn fat and keep muscle, like fasting but without the fasting.
The book's top 20 sirtfoods include kale, rocket, red onion, parsley, celery-like lovage, buckwheat, walnuts, strawberries, blueberries, capers, soy, extra virgin olive oil, turmeric, chilli, matcha green tea, coffee, dark chocolate and red wine.1
Phase one lasts a week. For three days you have three green juices and one meal, around 1,000 calories. For the next four days, two juices and two meals, around 1,500.1 Phase two is a two-week "maintenance" phase, and after that you're meant to keep eating plenty of sirtfoods.
How it works in your body
Sirtuins are real and they're fascinating. In yeast, worms and mice, boosting them has been linked to longer, healthier lives, and researchers are working on drugs to activate them.2 That's the solid part.
The wobbly part is everything after. The most famous "sirtuin activator", resveratrol from red wine, became controversial when a 2010 study found it and several drug candidates didn't directly activate the sirtuin protein at all; the effect in earlier experiments came from the lab test itself.3 The debate has gone back and forth since. Nobody has shown that eating kale and buckwheat switches on sirtuins in a human body enough to change fat loss.
What clearly happens in phase one: you eat about 1,000 calories a day. Your body uses up its stored carbohydrate (glycogen), which is held with water. When the glycogen goes, the water goes, and the scale drops fast.5 That's the famous "7 pounds in 7 days". It's not your skinny gene. It's your water.
What you eat, what you don't
Eat
- Kale, rocket, red onion, parsley, chicory
- Buckwheat (not wheat, gluten-free)
- Strawberries, blueberries
- Walnuts, extra virgin olive oil
- Soy, capers, turmeric, chilli
- Coffee, green tea, dark chocolate (85%)
Forget it
- Officially nothing is banned after week one
- In week one, almost everything except juice and one meal
- Sugar-heavy food (implied, not policed)
- Big portions of anything not on the list
A sirtfood day, without the juice
This is the version we'd actually recommend: the shopping list, normal portions, real protein, no green sludge.
- Breakfast: Greek or soy yoghurt with blueberries, strawberries and a few walnuts. Coffee or matcha.
- Lunch: buckwheat salad with rocket, red onion, parsley, capers, olive oil and a tin of tuna or a block of tofu.
- Dinner: salmon or chicken with kale fried in olive oil, a bit of chilli and turmeric, and potatoes or brown rice.
- After dinner: two squares of dark chocolate. Not the bar.
Nothing magic is happening to your genes here. It's just a very good day of eating.
In Singapore
Kale is pricey and often imported; kai lan (Chinese kale), spinach and other local greens do the same job on your plate. Buckwheat turns up as soba, but many soba noodles also contain wheat flour, so check the label if you avoid gluten. Matcha drinks in cafés are often more sugar than tea: ask for it unsweetened.
In Austria, Germany and Switzerland
You're in luck: Buchweizen is sold in most supermarkets and organic shops, Grünkohl is a winter staple, and walnuts and berries are local. Skip pricey "superfood" powders. A plate of Buchweizen with Grünkohl and a bit of fish costs less and has no marketing on it.
Alcohol on the Sirtfood diet
OK, now and then
- One glass of dry red wine with a meal
- A spritzer: dry wine with soda water
- A spirit with soda water and lime
Nope
- Red wine "for the resveratrol"
- Any alcohol during the 1,000-calorie days
- Cocktails, liqueurs, sweet wine
- Drinks mixed with juice, cola or tonic
50 Club: one glass of dry red, with food, because you like it. Not because it's medicine.
The diet sells red wine as a sirtfood. But in a study of 783 older Italians, the amount of resveratrol in their urine from diet wasn't linked to living longer or to less inflammation, heart disease or cancer.4 Alcohol, meanwhile, causes cancer, and WHO experts say no amount is safe for cancer risk.7 All the details are in our alcohol guide.
What it's good for, with proof
The food list is genuinely good
Take away the sirtuin story and you have leafy greens, berries, nuts, olive oil, onions, soy, buckwheat and herbs. That's basically the Mediterranean diet with a kale habit, and that pattern has decades of evidence behind it. No sirtuins required.
Weight loss, from calories
You will lose weight in week one, because 1,000 calories a day is a lot less than most people need. After that, any weight loss comes from eating less overall. A meta-analysis of named diets found weight loss was similar across very different programmes, and what mattered was sticking with them.6 Sirtfood has no published independent trial to say it does better.
The uncomfortable truth
"It activates your skinny gene." Sirtuins aren't a skinny gene, and no human study has shown sirtfoods switch them on enough to change body fat. The book's own early results came from a small pilot at a private gym, run by the authors, not a controlled trial in a journal. That's marketing, not evidence.
"You keep all your muscle." Any 1,000-calorie week with little protein risks muscle. There's no published data showing sirtfoods protect it.
The risks
- Low protein in week one. Juices have almost none. You'll be hungry, tired and short of protein.
- Juice, not fruit. Juicing strips out fibre. Green juices with apple can still spike blood sugar.
- Green tea extracts. Matcha as a drink is fine. Concentrated green tea catechin supplements at high doses have been linked to liver damage.8
- Medication interactions. Very large amounts of kale and parsley (vitamin K) can interfere with warfarin. Ask your doctor if you take blood thinners.
- Diabetes medication. 1,000 calories a day with insulin or sulfonylureas can cause low blood sugar.
Allergies: watch the staples
| Sirtfood staple | Allergen (EU list of 14)9 | Swap |
|---|---|---|
| Walnuts | Tree nuts | Pumpkin and sunflower seeds |
| Soy, tofu, miso | Soy | Lentils, chickpeas |
| Celery and lovage in the green juice | Celery | Cucumber, more kale |
| Dark chocolate | Often milk, soy, tree nuts (check label) | Allergen-free dark chocolate, berries |
| Buckwheat | Not on the EU list (gluten-free); buckwheat allergy exists but is rare | Quinoa, brown rice |
| Prawns in the recipes | Crustaceans | Chicken, tofu |
Don't do Sirtfood if you…
- are pregnant or breastfeeding
- have diabetes and take insulin or sulfonylureas
- take warfarin or other blood thinners
- have ever had an eating disorder
- are under 18
Healthen me asks about all of these and gives you a different plan if any apply.
How we use Sirtfood in your plan
We don't. Sirtfood is information only, not part of the plan.
The good bits are already in there: leafy greens, berries, walnuts, olive oil, onions and buckwheat show up all the time, because they're the backbone of the Mediterranean and anti-inflammatory patterns we use. The juice week isn't, and neither is red wine as medicine. If you want fast early results, read about crash diets first.
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
- Goggins A, Matten G. The Sirtfood Diet. London: Yellow Kite / Hodder & Stoughton, 2016.
- Bonkowski MS, Sinclair DA. Slowing ageing by design: the rise of NAD+ and sirtuin-activating compounds. Nature Reviews Molecular Cell Biology 2016;17(11):679–690. doi.org/10.1038/nrm.2016.93
- Pacholec M et al. SRT1720, SRT2183, SRT1460, and resveratrol are not direct activators of SIRT1. Journal of Biological Chemistry 2010;285(11):8340–8351. doi.org/10.1074/jbc.M109.088682
- Semba RD et al. Resveratrol levels and all-cause mortality in older community-dwelling adults. JAMA Internal Medicine 2014;174(7):1077–1084. doi.org/10.1001/jamainternmed.2014.1582
- Kreitzman SN, Coxon AY, Szaz KF. Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. American Journal of Clinical Nutrition 1992;56(1 Suppl):292S–293S. doi.org/10.1093/ajcn/56.1.292S
- Johnston BC et al. Comparison of weight loss among named diet programs in overweight and obese adults: a meta-analysis. JAMA 2014;312(9):923–933. doi.org/10.1001/jama.2014.10397
- Anderson BO et al. Health and cancer risks associated with low levels of alcohol consumption. Lancet Public Health 2023;8(1):e6–e7. doi.org/10.1016/S2468-2667(22)00317-6
- EFSA Panel on Food Additives and Nutrient Sources added to Food. Scientific opinion on the safety of green tea catechins. EFSA Journal 2018;16(4):5239. doi.org/10.2903/j.efsa.2018.5239
- Regulation (EU) No 1169/2011 on food information to consumers, Annex II (the 14 allergens). eur-lex.europa.eu/eli/reg/2011/1169/oj