There are many kinds of diets out there, and many claim to be great for weight loss. These diets focus on reducing your appetite, while others restrict calories, carbs or fats. So, let's get on to what these diets are and what is the science behind them.The Paleo DietThe paleo diet claims that you should eat the same food that your ancestors ate when they were hunters and gatherers. The word "paleo" comes from the Paleolithic era, when there were in fact, hunters and gatherers. The theory is that most modern diseases are linked with Western diet and it happens because of the consumption of processed foods, dairy and grains. While it is debatable if you can actually eat the food our ancestors ate, the diet does emphasizes on whole foods. It focuses on lean protein, vegetables, fruits, nuts, and seeds, while discourages processed foods, sugar, diary, and grains.In terms of weight loss, a 2007 study, A Palaeolithic diet improves glucose tolerance more than a Mediterranean-like diet in individuals with ischaemic heart disease, has shown that the paleo diet can actually lead to significant weight loss and reduced waist size.The Vegan DietLike the name suggests, the vegan diet is all things vegetarian and taking nothing from animals. So the dairy, the milk, the cheese, the honey, none of that is allowed. This is often known as the strictest form of vegetarianism. It seems to be very effective for weight loss, as the food is very low fat and high fiber. It makes you feel full for longer.As per a 2014 study, Low glycemic index vegan or low-calorie weight loss diets for women with polycystic ovary syndrome: a randomized controlled feasibility study, and many more such studies, vegan diets are linked to lower body weight and body mass index (BMI).Another 2013 study, titled: A multicenter randomized controlled trial of a plant-based nutrition program to reduce body weight and cardiovascular risk in the corporate setting: the GEICO study, which went on for 18 weeks showed that people on a vegan diet lost 9.3 pounds more than those on a control diet.Low-Carb DietsThese diets have been popular for decades and it involves limiting carb intake to 20 to 150 grams per day. The main aim of this diet is to force your body to use more fats for fuel than to using carbs as a main source of energy.Studies have indicated that low-carb diets are extremely helpful for weight loss, especially in overweight and obese people. As per a 2014 study, titled: A lower-carbohydrate, higher-fat diet reduces abdominal and intermuscular fat and increases insulin sensitivity in adults at risk of type 2 diabetes, these diets were effective at reducing dangerous belly fat, which can become lodged around your organs.People on very low-carb diets reach a state called ketosis, which leads to more than twice the weight loss than low-fat, calorie-restricted diet.The Dukan DietIt is a high-protein, low carb weight loss diet, which is split into four phases. The phases has two weight loss periods and two maintenance phases.In a 2015 study, titled: Assessment of food intakes for women adopting the high protein Dukan diet, women who followed the Dukan diet ate around 1,000 calories and 100 grams of protein per day and lost an average of 33 pounds in 8 to 10 weeks.Ultra Low-Fat DietThis diet restricts your consumption of fat to under 10% of daily calories. A generic low fat diet provides around 30% of its calories for fat, whereas in an ultra low-fat diet, it lowers down to 10% of total calories.The diet has been proven very successful for weight loss journey. In fact, an old study from 1975, titled: Treatment of massive obesity with rice/reduction diet program. An analysis of 106 patients with at least a 45-kg weight loss, found that obese people lost around 140 pounds on an ultra-low-fat diet. While another 8-week long study, titled: Culturally-sensitive weight loss program produces significant reduction in weight, blood pressure, and cholesterol in eight weeks, found that a diet that contained 7-14% of fat showed an average weight loss of 14.8 pounds.The Atkins DietThis is the most well-known low-carb weight loss diet and it helps you lose weight by eating as much protein and fat as you like, as long as your avoid carbs. It is also split in four phases, namely: induction phase where you eat under 20grams of carbs, then phases where you reintroduce healthy carbs back into your life.Studies show that this diet is a faster way to lose weight.The HCG DietThis is an extreme diet that is meant to cause very fast weight loss. It makes you lose 1 to 2 pounds per day. It also boosts your metabolism. It targets the HCG or the human chorionic gonadotropin hormone, which is present in high levels during pregnancy.The diet is split into three phases. During the first phase, you begin taking HCG supplements.During the second phase, you follow an ultra-low-calorie diet of only 500 calories per day, along with HCG supplement drops, pellets, injections, or sprays. The weight loss phase is prescribed for 3–6 weeks at a time.In the third phase, you stop taking HCG and slowly increase your food intake.While studies have shown that it causes weight loss, research found that more than HCG, the diet has to do a lot more with ultra-low-calorie diet.The Zone DietIt is a low-glycemic load diet that limits your carbs to 35 to 45%. The GI of a food is an estimate of how much it raises your blood glucose levels after consumption. It also helps reduce the risk of developing any chronic diseases. However, studies show that this diet is rather inconsistent.Intermittent FastingThis is one of the most popular words in the weight loss industry. It cycles your body between periods of fasting and eating. Instead of restricting the foods you eat, it controls when you eat it.There are several ways to follow intermittent fasting:The 16/8 Method: Skip breakfast and eat only within an 8-hour window, fasting for the remaining 16 hours.The Eat-Stop-Eat Method: Fast for 24 hours once or twice a week on non-consecutive days.The 5:2 Diet: Eat 500–600 calories on two non-consecutive days, with no restrictions on the other five days.The Warrior Diet: Consume small portions of raw fruits and vegetables during the day, followed by one large meal at night.In terms of weight loss, a 2015 study, titled: Fasting for weight loss: an effective strategy or latest dieting trend? intermittent fasting is very successful for weight loss. It has been shown to cause weight loss of 3 to 8% over a period of 3 to 24 weeks. It is a lot compared to most weight loss diets.