The Volumetrics Diet is a numbers game. With guidance from The Original Volumetrics Diet, a book by Penn State nutritional sciences professor Barbara Rolls, you'll learn to eat foods with fewer calories per gram aka "lower-density" foods. That means you'll eat fewer calories and still feel full. Volumetrics contains four food groups ranked by density in Categories 1 through 4. Category 1 contains the lowest-density foods, like non-starchy fruits and veggies and broth-based soup. The scale goes up to Category 4, which includes carb-heavy, fatty foods like crackers, oils, and cookies. You're encouraged to binge on the Category 1's, steer clear of the 4's, and focus mostly on the middle items like grains, fruits, and veggies. Foods high in water, like soup, fruits and veggies, and yogurt are encouraged, since water adds density without the expense of calories. You'll also lose weight: One study of 97 obese women on a low-energy-dense diet found they lost an average of 11 pounds over a year. In further good news, the fad diet has no restrictions and allows you to eat out as long as you stick to staple foods. Just make sure you like soup.

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It's no wonder MIND landed on our list -- it pulls brain foods from the Mediterranean and DASH diets for a plan that's geared towards cognitive health. Named the Mediterranean-DASH Intervention for Neurodegenerative Delay, the focus here is to lower your risk of Alzheimer's by eating from 10 brain-healthy food groups and avoiding unhealthy and processed food. You'll eat three servings of whole grains daily, along with a salad, veggie, and glass of wine. For protein, you'll eat chicken, fish, and nuts and snack on berries. Studies on MIND aren't geared towards weight loss, instead focusing on possible brain-healthy effects. But keep in mind that you'll be cutting out the fried food, dessert, and dairy that is typically tied to a higher calorie count. Bonus: Studies indicate you could also be reducing your chances of Alzheimer's by sticking with this popular diet.

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Despite its good word of mouth, the paleo diet scores poorly when it comes to weight loss, convenience factor, and long-term sustainability. The fad diet's popularity may come from the simplicity: The idea is to simply cut out any foods that wouldn't be available in the Paleolithic era. That leaves no room for processed foods, refined sugar, dairy, legumes, or grains. You're left with meats, fish, poultry and fruits and veggies. Critics claim that wiping out entire food groups is unsustainable in the long term, making the diet a difficult lifestyle choice. That's not to say it's impossible to lose weight. If you calculate calories to burn more than you eat, like with any other meal plan, you'll drop weight. But study results are slim. One "underpowered" study found that 14 participants lost an average of five pounds after three weeks. If you're a carnivore, however, there are plenty of recipes to choose from.

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Despite being one of the top searched diets of 2016, the ketogenic diet wasn't one of U.S. News' best 38 diets of the year. It's an extremely low-carb diet, high-fat diet that was originally developed to treat epilepsy. You'll also limit proteins. The fad diet is a "sustainable form of fasting," Gary Yellen, a Harvard Medical School professor, told TIME. Since your body typically relies on carbs for fuel and you won't be taking any in, you'll be eating healthy fats for energy. Research does suggest that it works to treat obesity. According to Today, a sample menu for the popular diet might include eggs with olive oil and avocado for breakfast, leafy greens, salmons, nuts and olive oil for lunch, and steak, greens and more oil for dinner. Ask a doctor or dietician before taking this one on.

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Whole30 was on everyone's mind this year, but popularity doesn't necessarily yield good results: The fad diet was last on U.S. News' report for the second year in a row. It's meant to be a lifestyle transformation, changing the way you think about food and even claiming to help with medical conditions. You'll restrict yourself to no sugar, alcohol, grains, legumes, or dairy, for 30 days. It's a difficult plan to maintain if you're not accustomed to cooking all your meals yourself or shopping for very specific ingredients. There are also no "cheat" snacks: No hemp cookies or chia pudding, because the plan hopes to change the way you think about food. On the bright side, plenty who have attempted Whole30 agreed that the month was a challenge, and are still thrilled to have survived those 30 days. There isn't much independent research on Whole30 specifically, but a survey by the company claims that 96 percent of dieters lost between 6 and 15 pounds. The plan does have sample grocery lists and plenty of online support groups, so if nothing else, you'll be in it with a team.

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