Fad diets are the fitness world’s equivalent to get-rich-quick schemes—they’re often too good to be true. But that doesn’t mean it’s not worth examining the principles behind these popular diets, and separating fact from fiction.
We spoke to Lilly Nhan, R.D., a clinical dietitian and current Master of Public Health candidate at the UC-Berkeley School of Public Health, about some of the top dieting trends on the market. We wanted to know: Do they work? Are they safe? And what practical information can we learn from them?
Here’s a close examination of seven popular weight-loss and diet methods, with Nhan’s analysis of what works—and what might be a waste of time.
1. Juice diets
The idea of “detoxifying” juice “cleanses” became big in 2007 when celebrities started crediting the Master Cleanse for massive weight loss. The restrictive and potentially dangerous fad has fallen out of favor since then, but it did pave the way for the current juice craze.
Juice diets can vary from substituting one meal with a juice (usually made from a combination of fresh fruits and vegetables, so put down that carton of OJ) to subsisting entirely on juices for a period of usually three to 10 days.
While there are nutritional benefits to juice—it’s a fast way to get vitamins and minerals—you’re better off eating fruits and vegetables in their whole form. “There’s more fiber in whole fruits and vegetables, so when you’re juicing, you’re throwing away all that nutritious fiber,” Nhan says.
And while juicing is a legitimate way to quickly reduce calorie intake, it’s not ideal long-term. “Fiber takes longer for your body to process, so when you have more fiber and complex carbohydrates, you feel more full,” she explains. “In contrast, when you’re drinking juice, it has a lot of sugar that’s going to get processed very quickly, and your body’s not going to register that as fullness. Your body has ways of compensating. You may drink that juice for breakfast, but at lunch and dinner you’ll wind up overeating to make up that calorie deficit.”
Recommendation: A juice fast or diet is a good way to “reset” your body in preparation for a more sustainable weight-loss regimen. Longer-term, it’s perfectly safe and healthy to replace a meal with juice, but instead of extracting juice, try blending whole fruits and vegetables into a smoothie or supplementing with fiber-rich foods to help stave off hunger.
2. Intermittent fasting
Intermittent fasting is hugely popular right now, thanks to a growing body of research backing its benefits. There are several types of intermittent fasting programs, ranging from 16-hour fasting periods followed by eight hours of “feeding” to alternating a full day of fasting with a day of normal eating. Preliminary research has shown that intermittent fasting is beneficial, although some programs require significantly more willpower than others.
“It’s a very promising area of research, although it’s a relatively new topic,” Nhan says. “The thing I would be wary of—and this is typical of any diet this restrictive—is that when you’re restricting yourself to an extreme degree, you can get into a cycle where you’re overcompensating by binging. That’s just not a healthy behavior around food.” Not all intermittent fasting programs are that extreme, Nhan points out, and many people who practice intermittent fasting can incorporate it well.
On a more practical level, intermittent fasting (and any highly restrictive diet) can disrupt social life, too: “If you’re on a fasting day and it’s a special occasion or your friends want to go out for dinner, it can adversely affect your lifestyle.”
Recommendation: Intermittent fasting is a safe and legitimate way to lose weight, according to current research. If you choose to start an intermittent fasting regimen, ease your way in with a less restrictive program like the 16/8 method before you graduate to a more extreme variation such as alternate-day fasting. Some even allow for fasting as your lifestyle permits. Be cautious about regulating your relationship with food, though. If at any point you begin to develop dangerous habits like binging and purging or restricting food for longer periods than the program dictates, stop the diet immediately, and seek help from a professional.
3. Paleo and keto diets
The Paleolithic diet (often the diet of choice for CrossFit athletes) and the ketogenic diet share similar principles, with some basic differences. The Paleo diet restricts legumes, grains, sugar, and most dairy. Carbs are allowed in the form of root vegetables and squash. The ketogenic diet shares a similar restriction list, with allowances for dairy and more stringent restrictions on carb intake. This high-fat, low-carb plan is meant to put the body into a metabolic, fat-burning state known as ketosis.
“People really latch on to these two diets in particular because you can see fast results if you adhere to them strictly,” Nhan says. “People achieve significant weight loss and report feeling better in general on them.”
But the biggest hurdle comes in terms of sustainability. “Most people are able to do the diet short-term, but it’s difficult to translate that really strict adherence into a lifestyle overall. They’re pretty expensive, and if you follow the diet exactly, being able to eat out and sharing food with others can also be difficult.”
Nhan has worked with patients to adopt ketogenic diets, which has been shown to help treat epilepsy, Alzheimer’s, and type-2 diabetes in a medical capacity. In those situations, she closely monitored their micro- and macronutrient intake and health status. “It can be dangerous to restrict your carbohydrate intake to such an extreme degree,” Nhan says. “Our bodies do need at baseline a certain amount of carbs and glucose, so when you’re restricting yourself, you can be at risk for certain adverse health events.”
Recommendations: Several tenets of the Paleo and keto diets are universally beneficial. Everyone should consider opting for high-quality carbs, limiting or eliminating all refined sugar, cutting out processed foods and refined grains, and eating more leafy vegetables. Replace carbs like pasta and white rice with spaghetti squash, sweet potatoes, riced cauliflower, and brown rice. If you do choose to fully adopt these diets, be aware that once you stop the weight will come back. If you’re an avid lifter, then you should read this before attempting the keto diet.
4. Carb cutting
“In general, most people over-consume carbohydrates—particularly refined carbs—so reducing your carbohydrate intake is generally a good idea,” Nhan says. Cutting carbohydrates can be a healthy move (although it can be problematic for people with hypoglycemia). But some people turn to extreme carb-cutting to lose fat, which has the potential for adverse effects (remember the Atkins Diet?) and the results are negated as soon as you stop.
Instead, Nhan recommends adopting some carb-cutting tricks without completely eliminating carbs. “Swap your carbs for vegetables—a lot of people are getting into cauliflower rice or spiralizing vegetables like zucchini into ‘zoodles,’” she says. “Across the board, most people do not consume enough vegetables, so I personally advocate for these techniques.”
Recommendation: Before you cut out carbs, focus on getting the best carbs possible. Refined carbohydrates strip out all the nutritional benefits of carbs, like fiber and vitamins. Opt instead for whole-wheat pasta and bread. If you’re willing to take the next step, start substituting rice and pasta with vegetables like spiralized zucchini, butternut squash, sweet potato, and riced broccoli and cauliflower. When you do eat carbs, go complex—farro, bulgur, quinoa, millet, and brown rice—which are absorbed much more slowly than refined grains.
5. The raw diet
The raw diet upside: It’ll undoubtedly help you lose weight by significantly reducing your calorie intake and increasing your fiber intake.
The downside of the raw diet: It’s incredibly restrictive, and requires superhuman amounts of willpower to maintain. Worse yet, there’s a point at which it can become very dangerous. Steve Jobs was famously a raw-foodist, and some speculate that it was a contributing factor in the pancreatic cancer that eventually killed him. Ashton Kutcher, who portrayed Jobs in his biopic, attempted the same diet for one month and it landed him in the hospital.
“My biggest concern about raw diets is getting enough protein and fats,” Nhan says. “People consume most protein in cooked form, whether it’s meat or vegetarian protein like beans. Fat is an essential macronutrient, and if you’re not preparing your foods with additional fats, you’re at risk for deficiency.”
On the flipside, raw foods do have their benefits. “A lot of times, during the cooking process, there’s the potential to have some of those vitamins or minerals leach out. By keeping them raw, there’s an opportunity to keep all the vitamins and nutrients contained within the food,” Nhan says. “But the caveat to that is that sometimes vitamins and minerals are activated by the cooking process, so there’s the other side of that coin.”
Recommendation: Choosing to do a raw diet can be beneficial in the short term, but we don’t recommend it long-term because of the stress on your liver and pancreas and the lack of protein. Of course, it’s beneficial to consume some vegetables raw, particularly nuts and seeds, berries, and onions. Meanwhile, carrots, tomatoes, spinach, and cruciferous vegetables benefit from being cooked.
6. Weight-loss teas
Diet teas? Hard pass, Nhan says.
While diet teas may help people achieve rapid weight loss, it’s definitely not a sustainable weight loss. “Usually diet teas are laxatives, and the weight that you’re losing is water weight. You’re not actually burning more calories,” she cautions. “Bodies are amazing and they do a lot of work to keep themselves in what’s called homeostasis, meaning keeping a balance in terms of hydration and electrolyte content. Eventually you’re going to—hopefully!—get that water back and that means gaining all that weight back.”
As with any aggressive weight-loss plan that revolves around an extreme water cut, be careful of going too far. “Abusing laxatives has serious health risks,” Nhan says. “Anyone committed to losing weight and keeping it off, I advise against diet teas.”
Recommendation: Unless you’re constipated and are using a diet tea sparingly for relief, we don’t recommend weight-loss teas.
7. The cabbage soup diet/grapefruit diet
These diets work on the philosophy that there are “negative-calorie foods,” which is to say that your body effectively burns calories digesting them.
But while the thermal effect of food (aka the energy your body expends to break down a food and absorb it) could theoretically offset the food item’s calorie content, the idea of “negative-calorie foods” is bogus, Nhan says.
“There is credence to the idea that some foods require more energy to absorb, but it doesn’t constitute a large portion of calories in your overall diet,” she explains. “Yes, if you’re eating cabbage and grapefruit and nothing else, of course you’re going to lose weight. But if you’re adding half a grapefruit or drinking cabbage soup every day with your normal diet, it’s not going to burn additional calories. That idea is totally false.”
Recommendation: Cabbage and grapefruit are both good for you. Eat as much of it as you like, but don’t expect it to magically singe off your love handles.
A final note about extreme diet plans
While most of these diets aren’t inherently bad for you, Nhan stresses that any form of extreme restriction can be difficult to maintain and create unhealthy mental hangups and behaviors around food. “The diets that work the best are the ones you can actually stick to,” she says. “You need to be able to incorporate the diet into your existing lifestyle, and that could mean a lot of learning and trial and error.” She emphasizes sustainable strategies like portion control, moderation, and smart substitution.
If you do need to lose weight fast, she recommends seeking the advice of a professional. “There are absolutely times when people want to lose weight fast. We hear about it all the time in celebrity culture when actors are losing weight for roles. The best way to do this is with the help of a professional like a registered dietitian, nutritionist, or personal trainer.” And brace yourself for some serious commitment. “If you want to lose weight that fast, it’ll require burning a lot of additional calories through exercise and high calorie restriction”—not to mention serious mental fortitude.