Which trendy diets actually work?

Diets are the new status symbol. Everyone's on one, and the one you choose says a lot more about you than how much you weigh. Still, in the end, what's the point of being fashionable if none of your clothes fit, you blow that promotion, and your kidneys are shot? Here, a panel of top nutrition and weight-loss experts explain which of today's trendiest diets you should try and which ones you should toss.

The Paleo Diet
"I've seen the most dramatic results from the Paleo Diet," Wesley Delbridge, R.D., a spokesperson for the Academy of Nutrition & Dietetics. "But I still wouldn't recommend it to anyone." That's because although it does a good job of cutting refined carbohydrates and processed foods—which is why people on it do tend to lose weight—it also bans healthy foods like whole grains, dairy, beans, and legumes. That puts you at risk for deficiencies in calcium and vitamin D, not to mention intense cravings, he says.

Still, the Paleo Diet loses most of its points for being so difficult to follow, says Despina Hyde, a registered dietitian at the Weight Management Program at NYU Langone Medical Center. With such a long list of taboo foods—ranging from canola oil and agave to all grains and coffee—eating out is difficult, and cooking is a complicated and pricey affair, he says. It's not full-Paleo, we know, but you'd probably be better off just eating fewer refined foods and calling it a day.

The Vegan Diet
"This one can either be really good or really bad, depending on how you do it," says Holly Herrington, R.D., L.D.N., a registered dietitian in the Center for Lifestyle Medicine at Northwestern Medicine. That's why, while research presented at the Obesity Society's 2013 meeting shows that people who follow a vegan diet lose more weight than do those who eat meat (even if they consume the same number of calories, mind you), a 2014 PLOS ONE study shows that people who cut out meat have higher incidences of cancer, allergies, and mental-health disorders than do the omnivores among us. After all, simply subtracting meat, eggs, and dairy from your plate isn't going to do much for you if you swap them out with junk.

The diet should be just as much about eating plants as it is about not eating anything animal-related, Delbridge says. However, even if you are loading up on fruits and veggies and not replacing your meat with processed faux meats or refined carbs, following a vegan diet still puts you at risk for nutritional deficiencies, most notably low B12, Herrington notes. According to a 2014 meta-analysis published in the European Journal of Clinical Nutrition, up to 86 percent of adults following a vegan diet are deficient in B12, which can cause poor energy levels, anemia, depression, cognitive decline, and rapid heartbeat.

The Gluten-Free Diet
If you have celiac disease or a gluten intolerance, this is the diet for you. Otherwise, you should move along. Eliminating foods that contain gluten, a protein found in wheat, barley, and rye, is an ineffective weight-loss strategy, says Hyde. After all, many GF foods are actually higher in fat, salt, sugar, and calories than their conventional counterparts. "When food manufacturers take out gluten, they have to replace it with something to preserve the taste and feel," she says. That's right, gluten-free cookies are even more fattening than regular ones.

Meanwhile, gluten-free flours, breads, and pastas contain less iron and B vitamins than do whole-wheat ones, Delbridge says. That sets dieters up for lackluster energy levels and possible anemia.

The Ketogenic Diet
What's with taking diets meant for people with disorders and slapping a "weight-loss" label on them? The Ketogenic Diet was developed for children suffering with epilepsy as a way to manage their seizures. Why it works, doctors aren't sure. But they do know that by cutting carbs drastically low, the body quickly burns through all of its stored carbs, called glycogen, which are housed in your liver and muscles. Since glycogen is attached to water molecules, you can lose a good five to 10 pounds of water weight in the first few days. It's a temporary fix, although it has long-term consequences," Delbridge says.

Your body has no choice but to run off of ketones, little carbon fragments created by the breakdown of fat, causing bad breath, dry mouth, tiredness, weakness, dizziness, insomnia, calcium loss, nausea, and potential liver and kidney damage, Hyde says. Also, since the brain is meant to run almost entirely on carbohydrates, brain fog during the diet is common, and research from Dartmouth Medical School states that even though it reduces the frequency of seizures in children, it may result in long-term memory trouble and shoddy brain growth.

The Mediterranean Diet
"If I had to support any diet in the world, it would be the Mediterranean Diet," Delbridge says. It's as balanced as "diets" get, according to Hyde, who notes that it's really not a diet but a lifestyle. "People like to say they are on a diet, though," she says. It prioritizes fresh fruits and vegetables, whole grains, beans, nuts, fish, olive oil, and even red wine. "It's really what we are designed to eat," Delbridge says. "It focuses on quality food and balanced meals of carbs, protein, fat, and fiber to aid in satiety and prevent insulin spikes, which can lead to cravings, insulin resistance, obesity, and type 2 diabetes. But it doesn't involve a huge restriction of calories."

That means you aren't going to lose weight fast on this diet, but that's actually a good thing if you want to lose weight without your body breaking down your muscles for fuel, Delbridge says. Plus, since it's incredibly doable, you can actually stick to the diet and keep off any weight you lose. For instance, a 2009 Harvard School of Public Health study found that nearly three times more Mediterranean dieters stick with their eating plans than do low-fat dieters. Meanwhile, according to a 2015 study from Harokopio University, adults who follow the diet are 47 percent less likely to develop heart disease. Did we mention heart disease is the No. 1 killer of men?

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