Mediterranean-area countries like Greece, Italy, and Spain are already known for their delicious food, but studies suggest that similarities amongst the local diets may also lead to heart health, weight loss, and diabetes and cancer prevention. A food pyramid crafted by the Harvard School of Public Health suggests adherents eat seafood weekly, skip red wine and red meat, and limit poultry and dairy. Suggested foods include fruits and veggies, beans, whole grains and, of course, olive oil. As U.S. News points out, the Mediterranean diet is "an eating pattern, and not a structured diet," so if you're focused on weight loss, speak with your doctor about a calorie target and fitness plan. But the popular diet has been proven to help with weight loss; a study following 259 overweight diabetics on the diet found that they lost an average of about 16 pounds over a year. There are plenty of recipe options that will please the dieter and the dieter's friend who loves Italian food.

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The flexitarian diet does away with what is often the most difficult part of dieting -- restriction. Coined by registered dietitian Dawn Jackson Blatner, the term combines "flexible" and "vegetarian" for a mostly vegetarian diet with room to grab a burger when you crave meat. You'll add five food groups -- fruits and veggies, whole grains, dairy, sugar and spice, and new "meats" like tofu and lentils -- to your diet, and snack twice daily. As a vegetarian, you'll likely eat fewer calories and still feel full. Add physical activity to your regimen, and the fad diet typically leads to weight loss. Data shows that vegetarians typically weight about 15 percent less than carnivores, with a lower Body Mass Index. Let Dr. Blatner's book be your guide for recipes, advice, and shopping lists.

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The Mayo Clinic Diet will walk you through two phases, intended to jumpstart weight loss then set up a new healthy lifestyle for long-term success. In the "Lose It" phase, which lasts only two weeks, you'll work out for 30 minutes daily, cut all sugar besides fruit, and stop eating in front of the TV. You'll eat lots of healthy fats and whole grains and start your day with a healthy breakfast. "Bonus habits" include cutting out processed food. The goal is to lose 6 to 10 pounds in this diet phase. After two weeks, the "Live It" phase is more lax on the rules, and gives you a calorie count to follow to either lose more weight or maintain what you lost during phase one. This popular diet ranks higher than some others on the "challenging" scale: You'll have difficulty eating out and largely won't be encouraged to drink alcohol. But while you're reaching for the carrot sticks for the tenth time in a day, take a small comfort in the fact that the Mayo Clinic medical center is highly qualified to develop a healthy diet that works.

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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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