The one thing that is sure to make you lose weight is this simple equation: CICO, short for “Calories In, Calories Out.” In short, it means: a) if you eat more calories than your body spends, you’ll gain weight; b) if you eat less calories than you spend, you’ll lose weight. In spite of all their differences, all diet plans that aim to help you lose weight must adhere to this seemingly simple equation. However, most experts agree that, by itself, CICO is an incomplete and flawed approach due mainly to its focus on quantity over quality, and the fact that it doesn't take nutrients into account.
When you drink liquid carbs, like the sugar in soda, your body doesn't register them the same way as, say, a piece of bread, according to a review of studies published in Current Opinion in Clinical Nutrition & Metabolic Care. That means, even though you're taking in calories, your fullness cues aren't likely to signal that you're satisfied once you finish off a can. And that can lead to consuming more overall.
Also some research shows that the human body is primed to consume most of its calories during daylight hours. But the lifestyle is problematic for many: Because family meals and dinners with friends often are scheduled for after sunset, "people who try to stop eating after 7pm can’t do it every day for the rest of their lives," says Dr. Seltzer, who supports an alternative strategy: Eating a hearty meal at your regular dinnertime.
On average, the daily caloric intake on Nutrisystem is 1,500 calories for men and 1,200 for women (low enough to lose weight but high enough to prevent “hangryness”). The daily menus are high in fiber to help you feel full, and are divided as follows: 50% carbs, 25% fat, 25% protein. According to a 2015 study by the American College of Physicians, people on Nutrisystem lose 3.8% more bodyweight than dieters who only receive guidance and counseling. Plus, thousands of positive customer reviews attest to Nutrisystem’s effectiveness, as long as you follow the program faithfully.
When you drink liquid carbs, like the sugar in soda, your body doesn't register them the same way as, say, a piece of bread, according to a review of studies published in Current Opinion in Clinical Nutrition & Metabolic Care. That means, even though you're taking in calories, your fullness cues aren't likely to signal that you're satisfied once you finish off a can. And that can lead to consuming more overall.
Phase 1: This is the “metabolism reboot” phase, and the most restrictive part of the plan (but it only lasts two weeks, so that’s good news). You’ll basically cut all carbs from your diet, as this phase allows for no more than 40 grams of net carbs per day. The purpose of this first phase is to reset your metabolism and help your body burn fat instead of carbs. Carb lovers beware! You will not be able to eat bread, pasta, rice, and some fruit, which might be too restrictive for some. Because of this strict approach, you’ll most definitely see weight loss results at the end of the plan’s first seven days.
"It's no big surprise, but my go-to weight loss tip is to eat more vegetables. They are the most low-calorie food you can consume, and they're filled with health-boosting, satiating nutrients. From smoothies and eggs to soups, main and side dishes, they can fit in anywhere and boost volume and nutrition. If you want to eat more while still losing weight, veggies are your answer. —Laura Burak, RD, CDN

While the jury is still out on carbs and saturated fats, one thing is clear: added sugars are no good. They contain what are called “empty calories,” and their overuse has been linked to an increased risk of obesity, diabetes, heart problems, and tooth decay. In fact, the USDA says no more than 10% of your daily calories should come from added sugars. 


Right now, this is the trendiest of all diet theories. It prioritizes the consumption of foods high in protein and fat while limiting the number of carbs per day to less than 20%. This means abstaining from grains, starchy vegetables, and fruits, and filling up on protein and fat. The most famous of all low-carb plans is the Keto Diet, an approach based on the metabolic process of ketosis, which happens when you restrict your carb intake to less than 0.7 grams per day and your body starts using fat, and not carbs, as its main fuel. 
There’s a large spectrum of where people can fall on a vegetarian diet: For example, vegans consume no animal products, whereas ovo-lacto vegetarians eat both dairy and eggs. The eating style may help with weight loss, suggests a review published in August 2017 in Nutrients, but some vegans and vegetarians may become deficient in specific nutrients, such as calcium, iron, zinc, and vitamin B12, according to an article published in December 2017 in Nutrition, Metabolism and Cardiovascular Diseases. (23,24)

Once you subscribe and place your order, each week you’ll receive fully prepared breakfasts, lunches, and dinners, (and also snacks or protein shakes, depending on the plan you choose). The items will come in a box that keeps food frozen for 6 to 8 hours, and each food packet is individually labeled and complete with its nutritional information. Also, all the 4-week plans allow for free shipping.
Safety: The history of dieting is filled with dangerous and downright life-threatening practices, from the fad of ingesting cotton balls to the infamous tapeworm diet. That's why, when looking for the best diet plan, nutritional balance and reduced caloric intake (usually 1,200 for women and 1,500 for men) are a must. After all, a diet is supposed to make you healthier, not make you sick.
If you’re only getting a minimal amount of sleep each night, that leaves more time for you to snack and make otherwise unhealthy decisions that could affect your weight loss. Although it will vary from person to person on how much sleep you actually need to be most effective (and therefore make progress toward your weight loss goals), the ideal number is typically 7 or 8 hours, says Dr. Cheskin. 

Ketosis is the metabolic basis for all “keto” or “ketogenic” diets. On a normal diet that includes carbohydrates (sugar and starchy foods), the body transforms these carbs into glucose, which is used as the body’s main source of energy. But, when we consume a minimum amount of carbs, the body will look elsewhere for that much-needed energy, and that “elsewhere” is fat. In short, when the body goes into ketosis, it is burning fat instead of carbs.
This may explain why the fat-burning effects of eating more protein were confirmed in a study published in the American Journal of Physiology. One group was fed a high-protein diet (just over 1 gram per pound of body weight per day) while the second group consumed an amount closer to the lower recommendation of the RDA (recommended dietary allowance). The group eating the higher-protein diet burned the most fat.
After a free diet analysis based on your Body Mass Index and submitting your ideal weight, Nutrisystem will recommend a plan to help you reach your goal. This plan is designed by nutritionists and allows for six meals a day (4 of them delivered by Nutrisystem and 2 to be prepared by you, following Nutrisystem’s guidance and recipes). This way you won’t be hungry for long, making it easier to stick to the diet plan until its completion.
Flexitarian: A mix between the words “flexible” and “vegetarian”, the Flexitarian diet can be described as a vegetarian going on a short carnivore vacation. It is a mostly vegetarian diet that sometimes incorporates meat, fish, and poultry, and it is ideal for people who want to benefit from vegetarianism but cannot resist the temptation of animal products.  Also, a recent study suggests that, by going meatless from time to time, you may actually help in the fight against climate change. 
The fad military diet consists of low-calorie, odd food pairings such as bun-less hot dogs with banana, carrots, and broccoli. “Any diet like the military diet that severely limits the amount of calories you consume or eliminates one or more entire food groups puts any individual at risk for nutrient deficiencies,” says Kyle. “This can be more harmful than holding onto those 10 extra lb you’re trying to lose.” (32)
A 2015 study from the Annals of Internal Medicine showed that for those who have a hard time following a strict diet, simplifying the weight loss approach by just increasing fiber intake can still lead to weight loss. Women should aim for at least 25 grams of fiber per day (based on a 2,000-calorie) diet, according to the most recent U.S. Dietary Guidelines. Start with our high-fiber diet plan.
Based on the concept of caloric density, which states that some foods have few calories in proportion to their size (say, a lettuce), while others have lots of calories packed in small portions (a regular chocolate chip cookie comes to mind), Volumetrics divides foods into 4 categories based on their calorie/volume ratio, and is perfect for people looking to binge on some foods while still shedding pounds. However, as with the calorie counting approach, Volumetrics does not take into account the quality of the calories, prioritizing quantity instead. The app Noom and Weight Watchers (both reviewed above) share similarities with this diet theory. 
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