Does the Sirtfood Diet Work? What a Dietitian Wants You to Know

Written by Robbie Clark, BExSc (Nutrition), M (Nutr+Diet), Accredited Practising Dietitian (APD) and Exercise Scientist · Last updated 28 October 2026 · 5 references

The Sirtfood Diet promises to "switch on" your body's fat-burning genes with foods like kale, dark chocolate and red wine. As a dietitian, I like that it encourages plant foods, but I have real concerns about its very low-energy start and its big claims. Here's what the evidence actually says.

What is the Sirtfood Diet?

The Sirtfood Diet is a commercial weight-loss plan built around "sirtfoods". It has two phases:

• Phase 1 (one week): for the first three days, about 4,200 kJ (1,000 calories) a day from three green juices and one meal. For the next four days, about 6,300 kJ (1,500 calories) from two juices and two meals.
• Phase 2 (two weeks): three sirtfood-rich meals and one green juice a day, without a set kilojoule target.

After that, you're encouraged to keep eating plenty of sirtfoods.

What are sirtfoods?

Sirtuins are enzymes in your body involved in how cells use energy. "Sirtfoods" are foods rich in plant compounds called polyphenols, which the diet's creators claim activate sirtuins. They include kale, rocket, parsley, onions, buckwheat, walnuts, strawberries, blueberries, extra virgin olive oil, green tea, coffee, dark chocolate, turmeric and red wine.

Most of the research on sirtuins and polyphenols such as resveratrol has been done in cells and animals. In human trials, resveratrol supplements led to only small reductions in weight and waist size, and results varied a lot between studies.¹ Those trials used concentrated supplements; the amounts in food are much smaller.

Does the Sirtfood Diet work for weight loss?

You'll probably lose weight in the first week, but not because of the sirtfoods. At about 4,200 kJ a day, you're eating less than half of the 8,700 kJ average adult reference (see what 8,700 kJ looks like), so you'd lose weight on any diet this low. Part of the early loss on very low-energy diets is fluid rather than fat.⁵

The Sirtfood Diet itself hasn't been tested in published clinical trials, so there's no evidence it helps you keep weight off.

What are the concerns with the Sirtfood Diet?

It has many of the warning signs of a fad diet: promises of fast weight loss, claims that particular foods "burn fat", rigid rules and a short-term plan with an end date.⁴

• Very low energy. It's hard to meet all your nutrient needs on 4,200 kJ a day, and very low-energy diets can cause tiredness, headaches and dizziness.^4,5
• Weight regain. After weight loss, hunger hormones change in ways that encourage eating, and these changes can last at least a year.³
• Your relationship with food. Strict rules and "good" and "bad" foods can lead to yo-yo dieting and, for some people, disordered eating.⁴

What works better for lasting weight loss?

Whether you lose weight quickly or slowly matters less than people think. In a trial, people who lost weight on a fast 12-week program or a slower 36-week program regained about the same proportion – around three-quarters – over the next three years.² What matters most is what you do once the "diet" ends.

That's why Dietitians Australia recommends a balanced, sustainable eating pattern based on the Australian Dietary Guidelines, regular activity and small changes you can keep for life.⁴ Many sirtfoods – leafy greens, berries, onions, walnuts, olive oil and buckwheat – fit easily into that kind of eating pattern without a crash phase.

Frequently asked questions

How much weight can you lose on the Sirtfood Diet?

You may lose a few kilos in the first week, but much of the early loss is fluid, and it comes from eating very little rather than from sirtfoods.⁵

Are sirtfoods healthy?

Yes. Most are nutritious plant foods, but there's no good evidence they have special fat-burning effects.¹

Is the Sirtfood Diet safe?

The first phase is very low in energy and isn't suitable for everyone, including people who are pregnant, under 18 or have a history of disordered eating.⁴

Does red wine help you lose weight?

No. Resveratrol supplements had only small effects on weight in trials, at doses far higher than you'd get from wine.¹

Is losing weight quickly worse than losing it slowly?

Not necessarily. In a trial, people regained a similar proportion of weight whether they lost it quickly or slowly.²

References

Research (PubMed)

1. Tabrizi R, Tamtaji OR, Lankarani KB, et al. The effects of resveratrol intake on weight loss: a systematic review and meta-analysis of randomized controlled trials. Crit Rev Food Sci Nutr. 2020;60(3):375–390. PubMed 30421960
2. Purcell K, Sumithran P, Prendergast LA, et al. The effect of rate of weight loss on long-term weight management: a randomised controlled trial. Lancet Diabetes Endocrinol. 2014;2(12):954–962. PubMed 25459211
3. Sumithran P, Prendergast LA, Delbridge E, et al. Long-term persistence of hormonal adaptations to weight loss. N Engl J Med. 2011;365(17):1597–1604. PubMed 22029981

Australian guidelines

4. Dietitians Australia. Fad diets. View source
5. healthdirect. Diet reviews. View source

This article is general information, not medical advice. Speak with your practitioner before starting any restrictive diet.