While it's likely that eating just 700 calories a day may cause some initial weight loss, the exact number of pounds will vary from person to person.
But keep in mind that following a very-low-calorie diet for quick weight loss can be unhealthy as well as counterproductive.
The Dangers of Low-Calorie Diets
The average adult needs somewhere in the range of 1,600 to 3,000 calories per day, per the National Institutes of Health (NIH). Although the exact number of calories a person requires depends on factors like age and physical activity, a 700-calorie diet is considered a very-low-calorie diet by any standard; even a sedentary 2-year-old requires at least 1,000 calories per day to meet their nutritional needs.
A moderately active 30-year-old needs anywhere from 2,000 to 2,800 calories a day to meet their body's nutritional requirements and stay healthy. If this person were to go from eating a 2,000-calorie diet to a 700-calorie diet in an effort to lose weight — cutting 1,300 calories a day — they could conceivably lose about 2.5 pounds a week, or roughly 10 pounds in a month.
When you drop pounds that quickly, though, it's likely at least some of the weight lost would be from muscle tissue instead of fat. Strength training could offset some of the lean muscle loss, but dieters often lack energy for such activity when eating so few calories.
Unfortunately, following a very-low-calorie diet makes it extremely difficult — if not impossible — to meet your body's nutritional needs. That's one reason why such rapid weight-loss efforts can lead to malnutrition, fatigue and generally feeling unwell.
Consuming too few calories can put your health at risk, per Harvard Health Publishing. Your body relies on a variety of foods for nutrients and health benefits, but a diet too low in calories would require cutting out a lot of those important foods, per the Academy of Nutrition and Dietetics.
You shouldn't overlook fiber, vitamins, minerals and other nutrients to reach a specific calorie target, as this could be detrimental to your immune system, bones, heart and other vital organs.
Rapid weight loss, which the NIH defines as losing more than 3 pounds per week, also significantly increases your risk of developing gallstones.
Aim for a Safe Calorie Deficit for Weight Loss
A gradual weight-loss rate is safer, easier to maintain and more likely to be successful than any rapid weight-loss effort. Losing 1 to 2 pounds per week is considered gradual, according to the Centers for Disease Control and Prevention (CDC).
This means cutting 500 to 1,000 calories per day, or 3,500 to 7,000 calories a week. This calorie range promotes weight loss without depriving your body of the nutrients you need to stay healthy, provided you make healthy, nutrient-dense dietary choices.
As for these nutrient-dense dietary choices? Most experts recommend prioritizing foods at the center of the Mediterranean diet, as they tend to be whole foods composed of a smart balance of protein, healthy fats and slow-burning carbohydrates.
Better yet, the Mediterranean diet appears to be more sustainable than other eating plans, including paleo and intermittent fasting, according to a December 2019 study in The American Journal of Clinical Nutrition.
To avoid slowing down your metabolism, the recommended minimum daily calorie level for weight-loss diets ranges from 1,200 to 1,800, depending on factors like your current weight, age and activity level, according to a September 2018 study in Healthcare.
Still, eating just 1,200 calories a day is considered a low-calorie diet for most people and can lead to unwanted changes in the body, like the increase of hormones that make you hungry, per October 2011 research in The New England Journal of Medicine.
Exercise is important when it comes to weight-loss success too. Not only does it rev up your metabolism, but it also helps you preserve the nutritional quality of your diet by allowing you to burn, rather than cut, some of your calories.
For the moderately active 30-year-old person who needs 2,000 calories a day, cutting those calories in half to lose 2 pounds per week can be challenging. Instead, burning 400 calories a day through exercise allows them to cut just 600 calories from their diet while achieving the same goal.
Cutting a few hundred calories a day can be as simple as serving yourself smaller portions at every meal, savoring your food as you eat so you're satisfied with less and drinking mostly calorie-free beverages such as water or unsweetened tea.
- National Institutes of Health: "Calories Needed Each Day"
- National Institutes of Health: "Gallstones"
- Centers for Disease Control and Prevention: "Losing Weight"
- Healthcare: "Defining the Optimal Dietary Approach for Safe, Effective and Sustainable Weight Loss in Overweight and Obese Adults"
- The New England Journal of Medicine: "Long-term persistence of hormonal adaptations to weight loss"
- The American Journal of Clinical Nutrition: "Intermittent fasting, Paleolithic, or Mediterranean diets in the real world: exploratory secondary analyses of a weight-loss trial that included choice of diet and exercise"
- Harvard Health Publishing: "Calorie counting made easy"
- Academy of Nutrition and Dietetics: "4 Ways Low-Calorie Diets Can Sabotage Your Health"