Adele has reportedly tried the Sirtfood diet, which promises to help you lose seven pounds in seven days.
The calorie-restrictive nature of the diet means it's likely not sustainable long term for weight loss. Jordan Strauss/Invision/AP
The Sirtfood diet, which Adele was first reported trying in 2017, requires you eat lots of "sirtfoods" to regulate the body's metabolism, inflammation levels, and aging. Sirtfoods, a "food group" not actually considered such by nutrition professionals, include green tea, citrus fruit, parsley, kale, capers, blueberries, apples, and even red wine.
At the start of the diet, you're supposed to restrict yourself to just 1,000 calories a day for three days straight. On days four through seven, you can eat 1,500 calories.
The calorie-restrictive nature of the diet means it's likely not sustainable long term for weight loss, and the short list of foods it provides could be limiting nutrient intake.
Adele has also credited pilates and cutting out tea, alcohol, and cigarettes for her current figure. "I used to cry but now I sweat," she wrote on Instagram.
Mariah Carey has said she eats nothing but Norwegian salmon and capers every day.
Carey said she tries to eat as much protein as possible. David Becker/Getty
"It's really hard," Carey said during an E! News interview in 2016. "My diet — you would hate it. All you eat is Norwegian salmon and capers every day — that's it."
She further clarified saying she tries to "stick to the proteins" and that it's "the worst."
Although eating protein can help keep you satiated, eating nothing but salmon means you won't get critical nutrients found foods like vegetables, fruits, and grains. It should go without saying that Carey's diet isn't sustainable for the long term.
Chris Pratt did a fast called the Daniel Diet, which is inspired by the Bible.
Pratt talked about the diet plan on his Instagram stories and challenged fans to join in with him. Frazer Harrison/Getty Images
Daniel dieters only eat fruits, vegetables, and unleavened bread for 21 days straight, with the overall goal of regaining focus on Christ-centered teachings, according to the Daniel Diet website.
Like other restrictive diets, the diet relies on the idea that the body needs to detoxify itself. But a special eating plan isn't necessary to make this happen.
"Diets that severely restrict calories or the types of food you eat usually don't lead to lasting weight loss and may not provide all the nutrients you need," the U.S. Department of Health and Human Services (HHS) explained on its website.
Actress Shailene Woodley eats clay regularly for its supposed detoxifying attributes.
"Clay is one of the best things you can put in your body," Shailene Woodley told a beauty blog. Experts disagree. Rodin Eckenroth/Getty Images
Known for her roles in "Divergent," "The Fault in Our Stars," and most recently, "Big Little Lies," Shailene Woodley has said she swallows a half teaspoon of clay in 8 ounces of water each morning.
"Clay is one of the best things you can put in your body," she told a beauty blog. Woodley allegedly heard about it from a taxi driver ,and says it "binds to other materials in your body" to help you get rid of "negative isotopes."
This is a bogus medical claim; your kidneys and liver don't need help processing toxins.
Clay might have trace amounts of some beneficial minerals, like iron and calcium, but there are better ways to obtain them (for instance, by eating foods rich in those minerals like spinach, broccoli, kale, and nuts).
Marilyn Monroe ate lots of raw eggs, steak, and hot fudge sundaes.
Monroe's diet could up your risk of salmonella poisoning. Getty Images/Stringer/Baron
In an 1952 interview, Monroe described her dieting choices as "absolutely bizarre," and she's not wrong. Eating raw eggs whipped into milk can lead to salmonella poisoning, and skipping lunch before a dinner of steak and five carrots could easily cause a dieter to lose out on essential nutrients. Monroe would also eat a hot fudge sundae for dessert, if you were wondering about her nightcap.
The late actress's diet appears to be an attempt at calorie restriction and a high-protein diet, but eating so little fiber and fresh produce could lead to nutrient deficiencies, heart problems, and a feeling of sluggishness.
Psychologist Jordan Peterson believes a meat-only diet can cure depression and give you more energy.
Following the meat-only diet endorsed by Jordan Peterson is likely to give you scurvy, since it lacks many essential nutrients. It's also expensive. Carlos Osorio/Getty Images
Jordan Peterson, the controversial University of Toronto psychologist, and his doctor Mikhaila have credited a diet of meat (and only meat) for curing a host of ailments, from arthritis to depression to gum disease. Peterson also said he lost 50 pounds since abstaining from other food groups.
Proponents of the "carnivore diet" say you should chose fattier meats over leaner versions and drink plenty of water.
But eating only meat means missing major pieces of a healthy diet, including fiber and vitamin C. (A lack of vitamin C intake can cause scurvy.) Eating red meat, particularly when it's high in fat, has also been linked to heart disease and certain types of cancer.
And with no dietary fiber in the mix, constipation is likely.
Plus, unless you're paying for high-quality, ethically sourced food, meeting all your caloric needs via animal products is really bad for the planet.
Nicole 'Snooki' Polizzi of 'Jersey Shore' fame ate cookies as part of a weight-loss regimen.
The cookies contain a "secret amino acid protein blend," according to the Cookie Diet official website, but still taste like normal cookies. Craig Barritt/Getty
In an effort to lose weight, Snooki did the Cookie Diet, which involves eating nine 90-calorie cookies daily in addition to a small meal at dinnertime.
The late Dr. Sanford Siegal created the plan in 1975 to help his patient eat fewer calories. The cookies contain a "secret amino acid protein blend," according to the Cookie Diet official website, but still taste like normal cookies.
Although the exact ingredients of the cookies are kept secret, the basic concept of eating one food for nearly every meal is unhealthy. It would require dieters to ensure their one dinnertime meal is packed with fresh veggies, protein, and other essential nutrients, and even then, a person may fall short of their daily nutrient intake needs.
Many celebrities, including Victoria's Secret model Miranda Kerr and actresses Jessica Alba and Blake Lively, have also been on the juice cleanse wagon.
Proponents say the cleanses flush the body of toxins and act as a dietary "reset." Getty/Gotham
Juice cleanses have become synonymous with celebrity diet culture. These cleanses are meant to flush the body of toxins and act as a dietary "reset," even though they aren't science-backed weight-loss methods.
Whether the cleanse involves forgoing meals altogether or replacing select meals with juice, the concept of a juice cleanse doesn't match up with human biology. The body has a built-in detox system that gets rid of toxins sans pricey sugar water.
"When we breathe, when we go to the bathroom, when our liver is functioning — the body does all the cleansing and detoxifying itself. There's no need to follow a certain diet plan to do that," registered dietitian Rachael Hartley previously told INSIDER.
Restricting calories so severely could certainly result in weight loss, but at the cost of feeling perpetually tired, hangry (hungry and angry), and being unable to keep the diet up for more than a week's time. If you tried for longer, you'd likely become nutrient deficient, experts say.
Twitter founder and CEO Jack Dorsey eats just one meal daily and fasts all weekend.
Jack Dorsey said he likes to do intermittent fasting. Getty
When Dorsey appeared on fitness author Ben Greenfield's podcast, he detailed his controversial diet, which involves eating just dinner every weeknight.
For his one daily meal, Dorsey has a protein (either fish, chicken, or steak), vegetables (an arugula or spinach salad, asparagus, or Brussels sprouts), and a dessert of mixed berries or dark chocolate, all of which he eats after 6:30 p.m. and before 9 p.m.
On weekends, Dorsey fats for the duration, only breaking his fast on Sunday night with bone broth. He has said the diet makes him feel more focused.
On Twitter, people said Dorsey's highly restrictive diet — an extreme type of intermittent fasting — could be a form of disordered eating, and experts agree.
"Animals who are starved shouldn't feel playful," Dr. Jennifer Gaudiani, CEDS, FAED, an internal-medicine doctor who specializes in eating disorders, previously told Business Insider. "They should feel concerned and focused. They may interpret that initially as productive, but it's the brain saying, 'I don't have enough food.'"
Tracy Anderson has put celebrity clients on the baby food diet — up to 14 jars a day of baby food with a normal meal for dinner, totaling no more than 1,400 calories.
Anderson recommends eating baby food for every meal except dinner to slim down. Instagram/Tracy Anderson
Celebrity trainer Tracy Anderson has endorsed this diet for weight loss.
The rules are simple: baby food for every meal except dinner, which should be a low-calorie mix of lean meat and veggies.
The diet allows for 14 jars of baby food or about 1,000 calories per day (plus a measly 400 for dinner). Even if you're trying to lose weight, experts recommend burning off around 500 more calories per day than you take in, meaning this just isn't enough food for most people.
That means if you try the diet, you're probably going to be spending a lot of time with a tiny spoon while still feeling hungry.
You can achieve the main benefit of this diet, the convenience of pre-portioned foods, with a little meal prep.
Late Chanel fashion designer Karl Lagerfeld drank up to 10 cans of Diet Coke daily and restricted his calories in the name of fashion.
Lagerfeld ate just 1,200 calories daily. FRANCOIS GUILLOT / Contributor
The story goes that Lagerfeld woke up one day and decided he no longer liked his body. He enlisted a doctor to help him lose 80 pounds, and then the duo wrote a book about it called "The Karl Lagerfeld Diet."
Lagerfeld, who died on February 19, 2019 at age 85, drank up to 10 cans of Diet Coke daily and ate small meals to restrict his calories. For breakfast, he'd have a piece of toast, one egg, juice, yogurt, and Diet Coke. For dinner, he'd have quail eggs, salmon and Brussels sprouts, or veal with plums.
The late Lagerfeld's diet is likely to make a person feel constantly hungry. He capped his calories at 1,200 per day, according to Vox, when men are recommended to eat 2,000 to 2,500 calories daily.
Plus, drinking lots of Diet Coke without eating enough could make you feel jittery. One study even found that drinking the beverage could increase the risk of stroke or heart disease.
Steve Jobs followed a strict "fruitarian" diet, at times limited to just apples and carrots.
Eating just fruits and some vegetables was part of Steve Jobs' eccentric reputation. YouTube/AllThingsD
The Apple founder named the corporation after one of his favorite foods following a visit to an orchard. But Jobs' passion for fruit goes further than that. He practiced a "fruitarian" diet, a stricter form of veganism limited to mainly fruits and some vegetables.
A bio of Jobs reports he would sometimes turn "a sunset-like orange hue" from his strange diet, and his obsession with fasting and extreme dietary restriction has been described as a full-blown eating disorder.
Ashton Kutcher ended up in the hospital after a month of this diet, which he followed in order to prepare to play Jobs in a biopic.
Fresh fruit and vegetables are both parts of a healthy, balanced diet. But alone, they lack adequate protein and fat, as well as necessary nutrients like vitamin B, calcium, and zinc. That much fructose can also strain your liver and heart.
Elizabeth Taylor wrote a diet book based on her own weight-loss recipes, including one for a hamburger and peanut butter sandwich.
Elizabeth Taylor had an eccentric list of recipes she created, and swore by, for weight loss, including some truly bizarre flavor combinations.
Around age 50, the actress once called "the most beautiful woman in the world" reportedly tried a diet plan to regain what she felt was her ideal body type by losing weight, but not too much. ("I began to lose my bust! Believe you me, I had to put on some flesh in a hurry," she once famously said of her weight loss.)
The diet was based on meals of her own creation including, most famously, the hamburger and peanut butter sandwich. Other Taylor-made recipes include tuna salad with grapefruit (served in the grapefruit rind for style points) and the Rock Hudson cocktail (Hershey's syrup, vodka, and Kahlua).
Some of Liz's tips are actually part of a healthy diet, like eating less red meat and more fish, fresh fruits, and vegetables. She was also an early champion of the cheat meal (her favorite was fried chicken and chocolate cake), which some research has been shown to help weight loss and promote sustainable dieting.
But her questionable flavor combinations – think steamed cucumbers and mashed potatoes with mint – presumably only "worked" because they were so unappealing to eat.
Madonna swears by a macrobiotic diet of soy, sea vegetables, and fermented foods.
This plan is not only very restrictive, it also makes it difficult to get enough major nutrients like calcium, iron, and B vitamins. Charles Sykes/Invision/AP
Macrobiotic foods including whole grains, soy, sea vegetables, and fermented stuff like sauerkraut and miso are the staples of Madonna's diet. She doesn't eat any wheat, eggs, meat, or dairy.
While fermented foods are well-regarded in the medical community for their ability to cultivate your gut flora, this plan is mostly full of downsides. It is not only very restrictive (and therefore probably not sustainable), it also makes it difficult to get enough major nutrients like calcium, iron, and B vitamins.
Victoria Beckham eats to optimize her PH level with the alkaline diet, which favors legumes and veggies and bans meat, grain, alcohol, and caffeine.
Another restrictive eating plan, the alkaline diet claims to balance your body's pH level by banning things like coffee. Evan Agostini/Getty Images
Victoria Beckham follows a diet plan designed to optimize pH balance with alkaline foods like fruits and vegetables, soy, legumes and nuts. The plan avoids meats, dairy, grains, eggs, meat, processed foods, caffeine, and alcohol.
pH refers to the scale from 0 (acidic, such as battery acid) to 15 (basic, like lye or bleach), with pure water in the middle. But your body naturally works to keep your levels stable, regardless of what you eat, according to the Columbia University's Irving Medical Center, so there's no proof this actually does anything.
The diet is also needlessly restrictive and, to do it properly, you're supposed to test the pH level of your urine regularly. While there are some benefits of the eating plan, they're mostly common-sense, like eating more vegetables and less red meat and junk food. Also coffee has plenty of benefits, so ditching it is not only needlessly hard but not that helpful for most people.
Elvis Presley was an early proponent of the "Sleeping Beauty Diet," or going to bed for 10 hours or more a day to avoid eating.
Elvis Presley, in his later years, resorted to sleeping long periods of time to lose weight, a trend now called the "Sleeping Beauty Diet." AP
The King of Rock and Roll was well known to have some eccentric eating habits. During his later years, when he struggled with obesity and associated health problems, his doctor recommended he use extra sleep as a means of weight loss. This unknown doctor of ill-repute was even rumored to have gone as far as using a medically-induced coma to help Presley shed some pounds.
The Sleeping Beauty Diet has experienced a resurgence in recent years, according to VICE.
At its most innocuous, this is a version of intermittent fasting. But at its worst, especially cases where drugs like Valium and Xanax are used to stay asleep, sleeping to avoid eating veers into serious eating disorder territory.
Research shows having enough sleep is important for a healthy metabolism, but overdoing it can have the opposite effect and reduce muscle mass.
Brooke Shields made the "grapefruit diet" famous. It includes 800 calories a day and lots of the pink citrus fruit.
The grapefruit diet used by Brooke Shields includes a severe calorie deficit. Getty/Cindy Ord
The grapefruit diet may help you lose weight, but only because of severe calorie restriction, not because of any magical enzyme the fruits contain.
The diet plan limits calories to just 800 a day, comprised of eggs in the morning, grapefruit all day, and a small piece of meat with veggies for dinner.
That kind of undereating can cause you to shed muscle mass, slow your metabolism, and, in severe cases, lead to serious problems due to malnutrition. It can also be dangerous to people already at risk of eating disorders.
That said, grapefruit does have some benefits, like vitamin C and potassium. But it blocks a specific enzyme related to breaking down some drugs, which can mean your body gets a higher dose, so be cautious about mixing it with your meds.
Gwyneth Paltrow's wellness brand Goop has written about numerous iffy diet practices, including a goat milk cleanse.
Gwyneth Paltrow created the controversial wellness brand Goop. Todd Williamson/Invision for Roadside Attractions/AP
In a 2017 Q&A on Goop.com, a "naturopathic physician" named Linda Lancaster suggested readers drink goat milk and nothing else for eight days straight to get rid of any parasites that might be in the body.
"In those days [biblical times], when a healer learned of a worm infestation, they would put the patient in a tub of milk until the worms would come out to drink—parasites love milk!" Lancaster said.
Not only is this advice lacking evidence, but drinking raw dairy could also lead to foodborne illness and subsequent hospitalization.
Christina Aguilera has done the 7-Day Color Diet, which involves eating foods of a different color each day of the week.
The same effects can be achieved if a person eats colorful, nutrient-dense meals every day of the week. Jerod Harris/Getty Images
Aguilera's diet was based off the 2003 book "7-Day Color Diet" by Jessica Weisel Courtney and Mindy Weisel.
Dieters are told to eat foods in only one color group each day, consuming items that are white, red, green, orange, purple, yellow, and rainbow, in that order. The thinking is that this way of grouping foods ensures dieters get all of their nutrients because different colored foods offer different ones, INSIDER previously reported.
Although limiting yourself to one color each day isn't unhealthy (so long as you eat mainly unprocessed, fresh foods), the same effects can be achieved if a person eats colorful, nutrient-dense meals every day of the week. The diet may be difficult to follow or unsustainable for some people, so eating a simple balanced and rainbow-colored diet daily is fine too.
Katy Perry's "M Plan" calls for replacing one meal a day with mushrooms, which offer a variety of health benefits.
Eating mushrooms like Katy Perry might not make you lose weight in problem areas, but it could still be good for you. Rich Fury/Stringer/Getty Images
Pop star Katy Perry reportedly turned to the M-Plan in 2013. Also called the "mushroom diet," it calls for substituting mushrooms for one meal each day — portobellos instead of a burger, for instance.
No one knows who came up with the idea, so you're relying on the collective internet wisdom with this one. Its main claim to fame, that you'll lose weight from so-called "problem areas" of the body, is unproven (experts generally agree it's impossible to spot reduce fat).
However, mushrooms are healthy and swapping them for a meat or pasta can help cut calories and add nutrients like zinc. They might even be good for your brain — some research suggests eating mushrooms can help keep your mind sharp later in life.
Magician Penn Jillette made 100 pounds vanish; his diet plan included two weeks of eating only potatoes.
Penn Jillette's most impressive magic trick may be his unique diet strategy. Getty/Ethan Miller
Jillette decided he need to lose weight and completely overhaul his lifestyle several years ago after doctors found a 90% blockage in his heart, according to Good Housekeeping.
The choice of potatoes was arbitrary, a sort of mental boot camp for restricting eating habits. "I picked potatoes because it's the funniest word," the 6-foot 7-inch magician told ABC.
Again, a mono diet — eating just one kind of food — doesn't provide the wide range of nutrients your body needs. Jillette said in the ABC interview that he "doesn't respect moderation," but that's exactly what's important in a healthy, balanced diet.
Jillette eventually did transition to a more sustainable, less restrictive diet still based mainly on veggies and whole foods. His weight loss "secret" may be the only one this magician reveals.
Kate Middleton reportedly did the high-protein Dukan diet to lose weight after having her first child.
Middleton used the diet to lose weight. Max Mumby/ Indigo/ Getty Images
The Duchess of Sussex reportedly went on the Dukan diet in order to lose weight quickly after giving birth to her first child. (Buckingham Palace denies this rumor.) The diet is a high-protein and low-carbohydrate plan.
Like the Atkins and ketogenic diets, two other high-protein plans, the Dukan Diet is known for helping dieters lose weight quickly. But the diet is difficult to maintain over time because of its restrictive nature. There are "phases" in place to prevent re-gaining weight after the diet, but it still was ranked 2019's worst diet, according to U.S. News & World Report.
"While the restrictive phases are short, they are very restrictive, so don't underestimate the willpower you'll need," concluded the outlet's analysis of the diet.
English poet Lord Byron added vinegar to everything because he was obsessed with being thin.
Romantic Lord Byron used vinegar to help curb his appetite as he underwent strenuous calorie-cutting episodes and lost an unhealthy amount of weight. Hulton Archive/Getty Images
The author of "Don Juan" was well known for his flamboyant excess, particularly in his love life. But Lord George Gordon Byron was also fanatic about his appearance, going to great lengths to cultivate the slim, pale look he considered fashionable.
One of those lengths was putting vinegar on everything.
Some people today swear by the health benefits of apple cider vinegar, and a small 2009 study did find consuming vinegar daily led to a small amount of weight loss.
But it's been theorized that Byron was anorexic — he was obsessed losing weight and severely limited his caloric intake.
When he did eat, it was reportedly just hard biscuits, soda water, and vinegar (sometimes with potatoes) to curb his appetite. He died at age 36 from a fever some suspect was the result of his severe weight fluctuations.
Robert Rhinehart's LA company has bought out version 2.0 of Soylent, which comes in the bottled liquid form and can be stored up to a year. The drink fulfills 20 percent of the daily requirement of essential minerals and vitamins and has 400 calories. Photo: Reuters/Mike Blake
© Avery Feinstein Avery Feinstein with her horse Rudy before she underwent bariatric surgery. Rudy has been by Feinstein's side during her weight loss journey. 
© Avery Feinstein Avery Feinstein lost 70% of her excess body weight and resolved her other health issues after surgery at age 18. 
© Avery Feinstein Avery Feinstein, 19, is now a student at the University of Missouri and "having the best time of my life," she says. 
© Avery Feinstein Avery Feinstein has maintained a healthy lifestyle since her weight loss surgery: "You have to do most of the work and the surgery is just a little bit of help," she says. 
© Provided by Cable News Network, Inc. Weightloss Surgery_00010706.jpg
Alternate day fasting may lead to successful weight loss. Photo: Image by PublicDomainPictures from Pixabay
A study in 2018 found that 31 percent of the U.S. population is at risk for one vitamin deficiency. Pixabay
