Adele’s weight loss success on the Sirtfood Diet came with lots of media attention for the diet. But does it really work?
If you had access to the internet back in May of last year, odds are you saw that picture of Adele. You know, the one where she is standing outside in a black dress and showing off her significant weight loss.
Immediately, millions of eager followers looking to lose weight themselves had to know: how did she do it?? Maybe you had a similar thought yourself, hoping that just maybe Adele had discovered a magic bullet to help accelerate weight loss.
Following the picture, multiple reports came out from popular news outlets that she was following an eating plan called the “Sirtfood Diet”, which became touted as the latest diet miracle, claiming to offer fast weight loss (we’re talking 7lbs in 7 days), while maintaining muscle mass and protecting against chronic disease (1).
Doesn’t that sound great!?
Well, let’s take a dive into the research and the popular discussion around the diet to see if it’s really worth your time, money, and effort.
Today we’re going to chat about what the Sirtfood Diet is, the scientific support for the diet (spoiler alert: it’s weak at best), and answer the key question in your mind when you saw Adele’s transformation: is it beneficial for fat loss?
In a nutshell, the Sirtfood Diet involves: extreme caloric restriction, green juices, and a list special “sirtfoods” that the creators of the diet claim increase the ability to burn fat.
But let’s break it down a bit further.
The Sirtfood Diet has a two-phased approach that lasts three weeks. During the first phase, your calories are limited to 1000 a day for three days. During this time, you’re only allowed to have three green juices and one meal that consists of the sirtfoods outlined in the book (2,3,4). Here is a list of some of the foods the authors classify as sirtfoods:
At first glance, there isn’t too much to critique about this list! A lot of these foods can be found easily and inexpensively at your local grocery store and most are highly nutrient dense, containing beneficial plant compounds known as phytochemicals. Plus, any plan that lets you eat coffee, chocolate, and red wine can’t be that bad right?
But let’s get back to these diet phases.
From day 4-7 of the diet, the final part of Phase 1, you move to a 1500 calorie limit, with two meals rich in sirtfoods and two green juices per day.
The green juice consumed throughout the diet is a powerhouse combination that includes many nutrient-dense ingredients. However, the book emphasizes that these vegetables should be juiced, not blended, meaning that the beneficial fiber found in these fruits and vegetables is removed. Here’s a rundown of what the green juice includes:
After the first week, you move on to Phase 2 of the plan, 14 days during which you should consume three meals daily that are high in sirtfoods and one green juice per day using the recipe above.
After the initial three week plan, the guidelines are less specific. There is no calorie recommendation, and you are encouraged to include as many sirtfoods in your meals as possible. You should also continue drinking one green juice per day. Additionally, you should aim for 30 minutes of exercise 5 days a week throughout the diet.
The authors note that after the first three weeks, Phases 1 and 2 can be repeated as many times as desired, to achieve additional weight loss results (2,3,4).
The Sirtfood Diet was developed by two celebrity nutritionists, both with Master’s degrees in Nutritional Medicine.
The creators of the diet wrote a book on the subject that includes the guidelines for following the diet, plus the recipes you need to adhere to it.
The book also describes a “pilot study” the authors conducted with participants at a fitness centre where they work. This study is the origin of the “7 pounds in 7 days” claim. It sounds magical, but unfortunately a Master’s degree and a pilot study don’t guarantee an evidence-based diet (2,3,4)
The pilot study that the authors claim they conducted has not been published anywhere besides in the authors’ own book, and therefore has not had to go through any kind of review process to examine whether the methods were sound and the results valid (2,3,4).
As a side note for those of you unfamiliar with the term “pilot study”, this is a small-scale study that is performed before a full-scale study in order to determine whether the researchers should proceed with a line of research (5).
But just because it’s small, doesn’t mean the researchers can throw away sound scientific practice.
Unsurprisingly, there are a couple points about this study that are…concerning. Maybe you spotted these issues yourself if you’ve taken an introductory statistics class at some point.
First, a single pilot study consisting of 39 participants is too low to draw any conclusive results about the effectiveness of a diet. A pilot study is supposed to be the basis for further research, not the basis for a book that draws readers in with unsubstantiated claims.
Additionally, we have no idea what the participants’ characteristics were at baseline. There is no indication of athletic background, lifestyle factors, and whether a random sample was used.
If you suddenly restrict the calories of a population of overweight individuals and have them exercise 5 days a week, is it any wonder they lose a significant amount of weight initially?
This raises another significant problem: the participants were not followed after completing the diet, so there is no way to know whether they regained the weight.
Despite many issues with the way this diet was tested, let’s now take a look at the research on sirtfoods and see whether the specific foods included in the diet have any scientific basis.
The Sirtfood Diet is based on the claim that certain foods activate a class of proteins in the body called sirtuins, which turn on a “skinny gene” that will accelerate weight loss (2,3,4).
Let’s get this out of the way immediately: there is no “skinny gene” that can be suddenly switched on to make you a fat-burning machine, so things are not looking good for the Sirtfood Diet right out of the gate.
However, there is some promising research coming out on sirtuins and their connection to longevity.
A calorie deficit (also known as caloric restriction) occurs when someone consumes fewer calories than they burn. Research has shown that a moderate calorie deficit, while ensuring all essential nutrients are still consumed, can increase longevity and health in lab animals (6). Caloric restriction is also associated with decreased risk of many age-related diseases, including diabetes, kidney disease, atherosclerosis, and cancer (7).
The beneficial effects of caloric restriction on extending lifespan and promoting health are largely due to the actions of sirtuins, and in particular one member of this family of enzymes called SIRT1.
SIRT1 senses caloric restriction, and in response more of this enzyme is produced in the body. The exact mechanisms of its beneficial effects on the body that lead to improved health are still being investigated (7).
One promising aspect of this research is the connection between diet and the activation of SIRT1. Phytochemicals, which are antioxidant-packed chemicals found in plants, have been shown to increase the amount of SIRT1 in the body in a similar way to caloric restriction. Foods that are significant sources of these phytochemicals can be considered sirtuin-activating, leading them to be termed “sirtfoods” (8).
In humans, caloric restriction can be difficult to sustain over a long period of time. Therefore, the possibility that the same result of increased longevity could be achieved with polyphenol consumption, without restricting calories, is an exciting concept (7).
While most of the research on sirtuins is related to longevity, the fat loss claims made by the creators of the Sirtfood Diet likely come from research done in cells and mice.
It’s been found that increased SIRT1 results in loss of fat from fat cells. Other research found that mice without the gene that produces the SIRT1 protein do not break down fatty acids in fat cells when in a fasted state, as is typically seen (9).
While the research above is interesting, it is important to note that none of it took place in humans. Additionally, very little was on fat loss, and while longevity is a better-studied outcome of consuming sirtfoods, the applicability of the research in humans has yet to be determined.
The short answer is yes, but before you throw your money at a diet book and a juicer, make sure to read on.
The truth is, you can lose weight on the Sirtfood Diet because you can lose weight on any diet that results in a calorie deficit. But losing fat is only part of the battle – the more significant concern is keeping that weight off, and this is where the Sirtfood Diet falls short.
Consuming 1000 calories a day is an extreme restriction that is well below the body’s energy needs and is highly unsustainable. Even when the daily caloric allowance is increased to 1500 calories, this is still too few calories for the majority of the adult population.
In the first week of the diet, significant weight loss may be seen due to the extreme calorie restriction, but much of this initial weight will be water weight, which will be regained when the individual begins eating normally again.
More problems arise if someone on the Sirtfood Diet follows the recommendation of repeating Phase 1 and 2 for further weight loss results, because this means an even longer period of caloric restriction. And honestly, most people on this diet probably have more weight to lose than can be achieved in 3 weeks, so continued restriction is very likely, and can have harmful effects.
Several research studies show that when obese patients are treated with low calorie diets, the maximum weight loss observed tends to be very small, primarily because of poor adherence. The body is not meant to subsist in a calorie-deprived state, and low calorie diets may result in overeating and binging (10).
Additionally, significant caloric restriction in the long term can cause fatigue, low mood, hormonal and reproductive issues, light-headedness, anemia, and slowed metabolism , as well as many other health concerns that increase in severity the longer caloric restriction goes on (11, 12, 13).
The issues with the Sirtfood Diet lie in the caloric restriction, not in the specific foods it recommends.
The research on sirtuin-activating foods does not say “severely restrict your calories and chug green juice all day,” and it definitely doesn’t mention a “skinny gene”. These were methods and claims developed by nutritionists trying to make money.
However, we can take the promising results found in the research on sirtuins and apply them in a non-restrictive way to our diets; the so called sirtfoods are high in antioxidants, they will help you meet your micronutrients needs, and many are high in fiber.
And if the research done in animals is transferable to humans, they might just help you live longer!
If you removed the significant calorie restriction component, this style of eating could contribute to sustainable weight loss, due to more home-cooked meals, more nutrient dense foods, and greater awareness of food choices.
However, it’s important to keep in mind that the answer when it comes to weight loss doesn’t lie only in food. You can change anything you want about your nutrition, but if you don’t reduce stress, get more sleep, and address other lifestyle factors, then weight loss is going to be an uphill battle.
When we pursue fat loss, there is often a tendency to eliminate groups of foods or adhere strictly to the rules of a fad diet, with the belief that there must be some secret to fat loss just waiting to be unlocked.
Unfortunately for those trying to lose weight, there is no secret. It’s not about the specific magic foods, or activating a “skinny gene”. Fat loss results come from the calorie restriction created by whatever recommendations the diet makes.
You can choose to create a calorie deficit with a restrictive diet that you will eventually go off and regain all the weight, or you can create one in a sustainable manner, such as by tracking macros.
Finally, having a dietitian on your team can help you sort out the nonsense from the advice that will actually help you get to the results you’re looking for. Save yourself the money you might spend on buying a diet book and focus on making long term changes and investments in your nutrition, without forgetting sleep, stress management, and movement that you enjoy.
And remember, if you need more support on making lifestyle changes, we are always here to support you! Don’t forget to join our Planos Nutrition Club Facebook Group, and consider applying to join our coaching programs.