Cutting calories is an important part of virtually any successful weight-loss plan. If you're motivated by quick results, it may be tempting to make drastic energy cuts and follow a very-low-calorie diet.
While there's no question that consuming just 700 calories a day will promote weight loss, the amount of weight you'd lose in a week depends on how many calories your body requires to maintain itself.
Unfortunately, following a very-low-calorie diet for quick weight loss can be unhealthy as well as counterproductive, and anyone attempting such a diet for more than a day or two should be monitored closely by a physician.
Calorie Balance Basics
Calories are a measure of the amount of energy supplied by food and beverages. Staying in caloric balance — or consuming just the level of calories your body needs to meet its basic metabolic requirements and sustain your overall activity level — plays a major role in your ability to maintain your body weight.
In much the same way, going into caloric excess — or routinely eating more calories than your body uses — can cause you to pack on pounds over time.
Shifting into caloric deficit — or eating fewer calories than your body requires, causing it to burn fat to meet its energy needs — is the basic principle behind weight loss.
Because a pound of fat stores 3,500 calories, creating a 3,500-calorie deficit generally results in a 1-pound weight loss. Though it may be tempting to create a major calorie deficit in an effort to speed up your loss, very-low-calorie diets generally do more harm than good.
Very-Low-Calorie Diet Dangers
The average adult needs somewhere in the range of 1,600 to 3,000 calories per day, according to the Center for Nutrition Policy and Promotion. Although the number of calories a person requires depends on gender, 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 his nutritional needs.
A moderately active 30-year-old woman needs about 2,000 calories a day to meet her body's nutritional requirements and stay healthy. If she were to go on a 700-calorie diet in an effort to lose weight – cutting 1,300 calories from her daily diet — she could conceivably lose about 2.5 pounds a week, or roughly 10 pounds in a month.
When dropping pounds quickly, however, it's likely some of the loss would be muscle tissue instead of fat. Strength training could offset some of the lean muscle loss, but dieters often lack energy for such activity when consuming 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.
Another health problem that can be brought on by rapid weight loss — defined by the National Institute of Diabetes and Digestive and Kidney Diseases as losing more than 3 pounds per week — is that it significantly increases your risk of developing gallstones.
A Safe Calorie Deficit for Weight Loss
A gradual weight-loss rate — which the Centers for Disease Control and Prevention defines as losing 1 to 2 pounds per week — is safer, easier to maintain and more likely to be successful than any rapid weight-loss effort.
This means that creating a calorie deficit of 500 to 1,000 calories per day, or eliminating 3,500 to 7,000 calories a week, promotes weight loss without depriving your body of the nutrients you need to stay healthy, provided you make healthy, nutrient-dense dietary choices.
To prevent a slowdown in metabolism, the recommended minimum daily calorie level for weight-loss diets is 1,200 calories for women and 1,800 for men, according to the American College of Sports Medicine.
Exercise is equally important as cutting calories when it comes to weight-loss success. 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 woman who needs about 2,000 calories a day, cutting her daily calories in half to lose 2 pounds per week can be challenging. Instead, burning 400 calories a day through exercise allows her to cut just 600 calories from her 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.
Benefits of Intermittent Fasting
Although drastically cutting your caloric intake isn't recommended as a safe or successful long-term weight-loss strategy, cutting your calories way back for short periods of time — with your doctor's approval — may help you lose weight and better control your body weight over the long haul.
The concept, known as intermittent fasting, typically involves eating a normal diet for several days or weeks, followed by one, two or several low-calorie days. Even though it's called "fasting," you do eat on those days, just in smaller amounts.
For example, an intermittent fasting plan that calls for fasting for five days a month might require you to consume 1,100 calories on the first day of your fast, then cut your intake down to 700 calories for the remaining four days, after which you go back to a normal calorie level for the rest of the month.
Other plans allow for two nonconsecutive "fasting" days a week when you eat 700 calories. In addition to recommending that you consume only whole, nutrient-dense foods, such plans generally spell out what percentage of your calories should come from fats, carbohydrates and protein, which is why it's wise to consult a dietitian before attempting intermittent fasting.
While weight loss can be a major benefit of intermittent fasting, it may provide other important health benefits, too. According to a study published in Cell Metabolism in 2015, intermittent fasting has been shown to extend longevity, boost immunity and improve cognitive performance in mice. In humans, the practice promotes beneficial changes in risk factors for age-related diseases such as diabetes, heart disease and cancer.
- Centers for Disease Control and Prevention: Finding a Balance
- Center for Nutrition Policy and Promotion: Estimated Calorie Needs per Day by Age, Gender, and Physical Activity Level
- Centers for Disease Control and Prevention: Losing Weight
- American Council on Exercise: Trimming Off the Fat
- NHS Choices: Should You Lose Weight Fast?
- National Institute of Diabetes and Digestive and Kidney Diseases: Dieting and Gallstones
- Cleveland Clinic: Intermittent Fasting Has Benefits Beyond Weight Loss
- Cell Metabolism: A Periodic Diet That Mimics Fasting Promotes Multi-System Regeneration, Enhanced Cognitive Performance, and Healthspan
- American College of Sports Medicine: Metabolism Is Modifiable With the Right Lifestyle Changes