The best low-cal diet plan isn't a diet so much as it is a method. CICO stands for "calories in, calories out" and is based on the mathematically sensible principle that as long as you're burning more calories than you're eating, you'll lose weight. All you need to get started is a way to track your calories—there are plenty of apps on the market although a pen and paper works great too—and a food scale to keep you honest about your portion sizes. (Also read this guide on how to safely cut calories to lose weight.) People love the simplicity and straightforwardness of the plan. And while it may not be the fastest way to lose weight, you're guaranteed to have success long term. (Just know that some weight-loss experts actually don't recommend calorie counting.)
While there are many vegetarian factions, all of them share the same basic dicta: no fish, meat, or poultry. But that’s where the similarities end for this eating plan/lifestyle practiced by 18% of the world population. Studies suggest that a vegetarian diet is good for reducing cancer risks, stabilizing blood sugar, and promoting heart health, while others raise a flag regarding nutritional deficiencies including Omega 3, vitamin B, calcium, and iron. Plans range from the most flexible to the most restrictive. Here are two of the most popular examples of each extreme:

"Your body begins to work differently. This study proves that small amounts of nourishment throughout the day are better than the same amount of food concentrated in three big sittings. If we feed the body at regular intervals we send a signal to the body that it doesn't have to store calories. Conversely, when we skip meals we send just the opposite signal for the body to store calories, creating a negative effect on the metabolism." — Dr. Wayne Scott Andersen, co-founder and Medical Director at Take Shape For Life
"Eating directly out of a box or bag (almost always leads to overeating. Serve your food on a plate or in a bowl to keep portion sizes in check and to get used to what one serving looks like. Also, when we take the time to sit down during meals versus standing or driving, we tend to feel more satisfied with our meal. In fact, research shows that you will eat up to 30% more food at the next meal if you ate standing up! Serve yourself, sit down, and enjoy!" — Jennifer McDaniel, MS, RDN, CSSD, LD, food and nutrition expert
Some diet plans, such as the MIND diet and the DASH diet, are meant to focus on certain areas of health — and weight loss may be a bonus. Others are created with weight loss as a primary goal. “It is important to remember that we are all very unique individuals,” says Kyle. “We all have different states of health and different lifestyles, which could affect what diet plan is best for us. That means that you should not be considering what is working for your friends or family members — and instead should pay attention to what works for you individually.”

Protein is also important for preserving muscle mass as you lose weight. If you cut back dramatically on calories and drop weight too fast, your muscles can suffer. Your body starts pulling from lean tissue like muscles and organs to fuel itself, and your metabolism slows to conserve energy. That’s why super restrictive diets that have you dropping weight fast aren’t healthy over the long run.
Make sure that the diet has been studied extensively for safety — and discuss any changes with your physician or registered dietitian before beginning a new diet. (If you don’t have a dietitian, find one in your area at the Academy of Nutrition and Dietetics website.) And do a self-check to ensure the diet fits with your own values and preferences.
The best diet for losing weight is Weight Watchers, according to the experts who rated the diets below for U.S. News. Volumetrics came in second, and the Flexitarian Diet, Jenny Craig and the vegan diet were third on this overall weight loss ranking list, which takes into account short-term and long-term weight loss scores. Some other diets performed as well or better in our rankings for enabling fast weight loss, but long-term weight loss is more important for your health.
If you want to lose weight fast, your best bet is the HMR Program, according to the health experts who rated the diets below for U.S. News. While these diets enable quick weight loss for those with a short-term goal – there's a strong chance you'll drop significant weight within the first 12 months – keep in mind that this is markedly different from long-term weight loss, which is more important for your health.

With this eating style, you’re looking at a lot of menu planning and preparation. A review published in August 2017 in Nutrients suggests the diet could lead to weight loss, but the Academy of Nutrition and Dietetics warns the plan could also cause certain nutrient deficiencies, such as in calcium and vitamin D. (3,4) And, therefore, according to an article published in the January–February 2016 issue of the Royal Australian College of General Practitioners, anyone at risk for osteoporosis should avoid it. (5)
There are many ways to do intermittent fasting — ranging from fasting for a number of hours each day up to an entire 24-hour fasting period one or two times a week. “If you're trying to kick a habit like eating late into the night, then stopping eating earlier in the evening and fasting overnight could be beneficial for you,” says Hultin. “There are many types of intermittent fasting, so ensuring you pick one that works for you and your lifestyle is important.”
Many diets, including Atkins and the keto diet, fit into this umbrella. A typical low-carb diet limits carbs to less than 60 g daily, but this can vary, according to the Mayo Clinic. (15) In a September 2015 review published in PLoS One, people following low-carb diets saw modest weight loss — although study authors note that long-term effects of the diet require further research. (16)
In practice, this means salt is substituted with herbs and spices. There are two models: the Standard Model, which recommends less than 2,300 milligrams of sodium per day, and the Low Sodium Model, which recommends less than 1,500 milligrams of sodium per day. Studies suggest DASH is also good for preventing osteoporosis, cancer, heart disease, and diabetes.
Popularized by the documentary Forks Over Knives, the Ornish diet is a low-fat, plant-based diet plan based on whole grains, vegetables, fruits, and legumes. It's based on a lacto-ovo style of vegetarianism, allowing only egg whites and nonfat dairy products. It's packed with vitamins, fiber, and lots of filling plants to keep you satiated. Some studies have shown it can reverse heart disease and have beneficial effects on other chronic health conditions. (BTW, there is a difference between a vegan diet and a plant-based diet.)
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