A low-calorie diet (LCD) is a tried-and-true approach to weight management for people who are overweight or have obesity, but it's important not to take it to extremes.
An LCD involves eating 1,200 to 1,500 calories per day for females and 1,500 to 1,800 calories per day for males. It can help you lose weight quickly.
LCDs are generally safe to maintain until reaching your goal weight, so long as you choose nutritious foods and don’t feel too hungry all the time.
So, does that mean you’ll lose weight even faster by reducing to 1,000 calories per day? Technically, you may quicken your results by following a very-low-calorie diet (VLCD), but it can cause adverse effects. Moreover, rapid weight loss may be unsafe and unsustainable over the long term.
Effects of Reducing Calories to 1,000 per Day
People who follow LCDs and VLCDs often eat meal replacement shakes, soups, and bars in place of regular meals. Others use juice diets or fasting for set periods to keep their calories low.
Whichever method you use, consuming only 1,000 calories per day presents several health risks.
Malnutrition
One of the risks of eating fewer calories is missing out on the protein, fat, carbohydrates, vitamins, and minerals that accompany those calories. If your body doesn’t get nutrients in the amounts it needs to function, malnutrition can occur.
“The standard 2,000-calories-per-day diet that lines up with U.S. Food and Drug Administration recommendations essentially provides the general recommended nutrient needs,” says Sarah Koszyk, RDN, a registered dietitian-nutritionist in San Francisco.
If you’re cutting that diet in half, your micronutrient intake will likely be cut in half, too. “A low-calorie diet can result in vitamin A, B, C, D, E, and K deficiencies, in addition to minerals like calcium, magnesium, iron, potassium, and zinc,” Koszyk says.
The symptoms and risks of malnutrition vary depending on the nutrient in which you have a deficiency and how long it lasts. But malnutrition can cause:
Bone and muscle loss
Weakness
Fatigue
Hair loss
Low heart rate and blood pressure
Frequent infections
“Your body can shut down over time if it’s not getting the nutrients it needs to sustain itself,” Koszyk adds.
Slower Metabolism
Following an LCD or VLCD can lead to dramatic weight loss — at least in the beginning.
But the rapid weight loss often seen with a 1,000-calorie diet can slow your resting metabolic rate, or how many calories you burn at rest. This can contribute to weight regain and sabotage your weight loss efforts over time.
“When people lose weight, their resting metabolic rate slows down to adjust to the body’s reduced energy needs,” Koszyk says. Eventually, your body stops responding to the calorie deficit.
Rapid and extreme weight loss also disrupts the hormones that regulate appetite. Your body produces less of a hormone that tells your brain when you’re full, called leptin, and more of a hormone that tells you when to eat, called ghrelin. This combination increases your urge to eat, which can make maintaining your rigid diet more challenging.
All of these factors make weight regain more likely after a drastic calorie deficit.
Reduced Mental Edge
Your brain needs a constant supply of glucose, or blood sugar, to function at its best. If you’re trying to get through the day on very little food, your brain won’t work as well as it should.
A review of 33 studies on calorie restriction and cognitive performance focused on which parts of cognition calorie restriction may affect. Researchers found that although continuous calorie restriction benefited participants on tests measuring self-control, speed of thought, and short-term memory, it affected their ability to switch between tasks or adapt to new situations.
Gallstones
Rapid weight loss can lead to gallstones. These are hard deposits of a digestive fluid called bile that the liver produces. Gallstones can develop in the gallbladder and cause sudden, intense, upper right or central abdominal pain as well as back or right shoulder pain, nausea, or vomiting.
When you lose weight quickly, your body breaks down fat for energy, causing the liver to secrete more cholesterol into the bile. This causes the bile to become saturated, which is harder for the gallbladder to release. Over time, gallstones may then develop.
Many people don’t develop symptoms from gallstones and won’t require treatment. However, if gallstones cause blockage or inflammation, you might need surgery to remove the gallbladder or medications to break down the gallstones.
Safety During Exercise on a 1,000-Calorie Diet
Regular exercise is important for overall health. Physical activity improves mood, blood pressure, and sleep. It also lowers your risk of heart disease, type 2 diabetes, and cancer. It can also help you reach and maintain a healthy weight by contributing to your daily calorie deficit.
But if your calorie deficit is already significant, exercising while following a VLCD can be risky unless you’re working with a healthcare professional who can keep tabs on you.
“A common side effect of low-calorie diets is fatigue and low energy,” Koszyk says. Without enough calories to power your workouts, you can get lightheaded, dizzy, or nauseated.
In addition, exercise requires adequate nutrients for recovery. “With a very-low-calorie diet, you may not get the necessary protein and nutrients post-workout, which can result in injury, deficiencies, fatigue, and muscle loss,” Koszyk says.
Consult a healthcare professional before combining an LCD or VLCD with exercise.
How Fast Will You Lose Weight on 1,000 Calories per Day?
Experts generally recommend a calorie deficit of 500 to 750 calories per day to lose about 1 to 2 pounds per week.
You may lose about 2 pounds per week by reducing your intake to 1,000 calories per day. However, your speed of weight loss at this (or any) calorie intake can vary depending on your age, environment, genes, stress levels, hormone levels, medications, and medical conditions.
Work with a registered dietitian to calculate a calorie intake that creates the most effective deficit for you.
When Would People Use a Very-Low-Calorie Diet?
Some clinical circumstances may make a VLCD necessary. For example, physicians often recommend it to reach a specific weight before bariatric surgery, also known as weight loss surgery. A person should only follow this diet under strict supervision from a doctor or registered dietitian.
Most experts recommend following a VLCD for no more than 12 weeks. However, your doctor or registered dietitian will determine a safe and effective length for you if they deem a VLCD appropriate.
Who Shouldn’t Eat a 1,000-Calorie Diet?
A 1,000-calorie diet is generally not a good idea, but people in some groups need to be especially careful not to let their calories drop so low.
Pregnant people generally need 300 calories more per day than they did pre-pregnancy from nutrient-dense sources to support the growing fetus. Eating only 1,000 calories per day can increase the risk of nutrient deficiencies and cause harm to the growth and development of the fetus, Koszyk says.
Also, mothers who are breastfeeding need an additional 340 to 400 calories per day or may experience a reduction in their milk supply and nutrition deficiency if they’re not getting proper nutrition.
Older adults with frailty, meaning reduced function and health, should also avoid VLCDs, as nutrient deficiencies can worsen bone and muscle loss, says Koszyk.
“Even people with diabetes, chronic kidney disease, or cardiac arrhythmias shouldn’t follow a 1,000-calorie diet unless medically supervised because of the potential complications that can occur,” she says.
The Takeaway
Weight loss can yield many health benefits for people who are overweight or have obesity. However, trying to lose weight quickly by consuming only 1,000 calories per day can be risky.
Eating only 1,000 calories per day can lead to malnutrition, slow metabolism, impaired thinking, and an increased risk of gallstones.
Some people may need to follow a low-calorie or very-low-calorie diet to prepare for bariatric surgery, but only when supervised by a medical professional.
For others, it’s best to lose weight with slow, sustainable lifestyle habits rather than extreme, abrupt diet changes.
If you have concerns about body weight, discuss a steady, sustainable weight management plan with a registered dietitian or physician.
EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
Diet for Rapid Weight Loss. MedlinePlus. May 20, 2024.
O’Leary J et al. The impact of continuous calorie restriction and fasting on cognition in adults without eating disorders. Nutrition Reviews. January 23, 2024.
Tara Collingwood, RDN, is a board-certified specialist in sports dietetics, an American College of Sports Medicine–certified personal trainer, and a media spokesperson. As a sports dietitian, she has worked with the U.S. Tennis Association, the Orlando Magic, World Wrestling Entertainment, runDisney, the University of Central Florida, and numerous professional and amateur athletes. Collingwood is the author of Pregnancy Cooking and Nutrition for Dummies and a coauthor of the Flat Belly Cookbook for Dummies.
She appears regularly on national and local TV, and speaks around the world to business teams on how to manage energy physically, emotionally, mentally, and spiritually. She previously served as a national spokesperson for the Academy of Nutrition and Dietetics.
Collingwood double-majored in dietetics as well as nutrition, fitness, and health at Purdue University and earned a master's degree in health promotion from Purdue University.
Lauren Bedosky is an experienced health and fitness writer. She regularly contributes to top websites and publications like Men's Health, Women's Health, MyFitnessPal, SilverSneakers, Runner's World, Experience Life, Prevention, AARP, Blue Cross and Blue Shield, UnitedHealthcare, Livestrong, Fitness, Shape, Family Circle, Healthline, Self, Redbook, and Women's Running.
When she's not writing about health and fitness — her favorite topics being anything related to running and strength training — she's reading up on the latest and greatest news in the field and working on her own health goals.
