A 1,000-calorie diet plan is an eating strategy that drastically cuts the number of calories a person consumes each day. Extreme diets have undesirable effects and do not result in sustained weight loss. While a very low-calorie diet may result in a loss of 3 to 5 pounds per week, for an average total weight loss of 44 pounds over 12 weeks, drastically cutting calories does not typically result in sustained weight loss and may be harmful. Instead, it is better to reach a moderate weight gradually with a balanced diet that a person can follow long term.
Understanding Calorie Needs
The term calorie describes the amount of energy in foods or drinks. The human body requires this energy to fuel essential metabolic processes. The number of calories an individual needs each day varies based on biological sex, height, weight, activity level, and genetics. According to the Dietary Guidelines for Americans 2020-2025, the average female adult needs about 1,800-2,400 calories daily, while the average male adult needs about 2,400-3,200 calories. Some foods are very high in calories, and consuming too many of these types of food may mean that a person takes in more calories than they need. High calorie foods to avoid or limit when aiming to achieve a moderate weight include: butter, oil, syrup, cream, cheese, pizza, and desserts.
Being in a calorie deficit aids weight loss. A calorie deficit means using up more calories than you intake. However, research has not identified the optimal deficit, and it likely depends on the individual. Although some diet plans may recommend consuming 1,000 calories a day or less as an effective tool for weight loss, it is not safe and is an unsustainable way to try and lose weight.
What is a Rapid Weight Loss Diet?
Rapid weight loss diet is a type of diet in which you lose more than 2 pounds (1 kilogram, kg) a week over several weeks. To lose weight this quickly you eat very few calories. These diets are most often chosen by people with obesity who want to lose weight quickly. These diets are less commonly recommended by health care providers. People on these diets should be followed closely by a provider. Rapid weight loss may not be safe for some people to do on their own.
These diets are only to be used for a short time and are usually not recommended for more than several weeks.
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People who lose weight very quickly are much more likely to regain the weight over time than people who lose weight slowly through less drastic diet changes and physical activity. The weight loss is a bigger stress for the body, and the hormonal response to the weight loss is much stronger.
Types of Rapid Weight Loss Diets
Several types of diets severely restrict calories to achieve rapid weight loss. These include very low-calorie diets (VLCDs), low-calorie diets (LCDs), time-restricted eating, intermittent fasting, and fad diets. In some cases, these diets are not safe. In most cases, these diets are not sustainable for long enough to cause long-term weight loss. Once you stop the diet, you are at risk for regaining the weight if you return to your old eating habits.
Very Low-Calorie Diets (VLCDs)
Most VLCDs use meal replacements, such as formulas, soups, shakes, and bars instead of regular meals. This helps ensure that you get all of the nutrients you need each day. A VLCD is only recommended for adults who have obesity and need to lose weight for health reasons. These diets are often used before weight-loss surgery. You should only use a VLCD with the help of your provider. Most experts do not recommend using a VLCD for more than 12 weeks.
Low-Calorie Diets (LCDs)
These diets usually allow about 1,000 to 1,200 calories a day for women and 1,200 to 1,600 calories a day for men. An LCD is a better choice than a VLCD for most people who want to lose weight quickly. But you should still be supervised by a provider. You will not lose weight as fast with an LCD, but you can lose just as much weight with a VLCD. An LCD may use a mix of meal replacements and regular food. This makes it easier to follow than a VLCD.
Time-Restricted Eating
This diet strategy is becoming more popular. It is often compared to fasting, but the two strategies are slightly different. Time-restricted eating limits the number of hours per day that you can eat. A popular strategy is the 16:8. For this diet, you have to eat all of your meals during an 8 hour period, for example, 10 am to 6 pm. The rest of the time you cannot eat anything.
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Intermittent Fasting
Fasting is an ancient form of caloric restriction. It has become more popular recently. This is partly because some animal and human studies have shown benefits to fasting for people with diabetes and obesity. There are many different fasting regimens and it is unclear which may be the best. One of the most popular is the 5:2 system. This involves 2 days a week of fasting or VLCD and 5 days a week of eating your normal diet.
Fad Diets
Some fad diets also severely limit calories to achieve rapid weight loss. In some cases, these diets are not safe. In most cases, these diets are not sustainable for long enough to cause long-term weight loss. Once you stop the diet, you are at risk for regaining the weight if you return to your old eating habits. Others, such as the well-known grapefruit diet, rely on eating a lot of the same low-calorie food or foods.
Risks Associated with a 1,000 Calorie Diet
While some evidence shows that these diets can promote weight loss, most people cannot sustain it and often experience significant weight regain. The reasons include regaining lost muscle mass and increased appetite. Also worth noting is that the human body can adapt. Significantly decreasing caloric intake causes the body to decrease the energy it burns. Typically, when individuals increase their calorie intake, they regain the lost weight. They may even gain more weight because they are in a caloric surplus, which means they eat more calories than their body needs to function.
Extreme reductions in calorie intake can cause harmful side effects, such as: dizziness, extreme hunger, gallstones, nausea, fatigue, headaches, and nutrient deficiencies. These diets can also change specific metabolic pathways inside the body. For example, they can change hormones such as ghrelin and cortisol, which play a role in feelings of hunger. They can also decrease muscle mass and affect the number of calories the body uses each day. This increases the risk for weight regain once an individual no longer maintains the diet.
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. 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.
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Malnutrition
One of the risks of eating fewer calories is missing out on the protein, fat, carbohydrates, vitamins, and minerals that accompany those calories. “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 and frequent infections. “Your body can shut down over time if it’s not getting the nutrients it needs to sustain itself,” Koszyk adds. To be healthy, you need a balance of foods from different food groups. It's difficult to get good nutrition and feel satisfied on a very low-calorie diet. Most people on very low calorie diets need vitamin and mineral supplements to ensure they are getting proper nutrition.
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. Gallstones are more common during rapid weight loss. When the body experiences a calorie deficit, it starts to break down fat for energy. The liver then secretes more cholesterol and when combined with bile, can form gallstones. However, if gallstones cause blockage or inflammation, you might need surgery to remove the gallbladder or medications to break down the gallstones.
Other Potential Health Concerns
You should only follow one of these diets with the help of your provider. Losing more than 1 or 2 pounds (0.5 to 1 kg) a week is not safe for most people. It can cause you to lose muscle, water, and bone density. Rapid weight loss can also cause some side effects including: Gallstones, gout, fatigue, constipation, diarrhea, and nausea. People who lose weight quickly are also more likely to gain back the weight quickly. This can lead to other health problems. In general, a rapid weight loss diet is not safe for children. It may also not be safe for teens, pregnant women or older adults unless a provider recommends it. People on a very low-calorie diet for 4 to 16 weeks report minor side effects such as fatigue, constipation, nausea, and diarrhea. These conditions usually improve within a few weeks and rarely prevent people from completing the program. Very low-calorie-diets are not recommended for pregnant or breastfeeding women, and are not appropriate for children or teens except in specialized treatment programs. They also may not be OK for people over age 50, either, depending on the potential need for medications for pre-existing conditions, as well as the possibility of side effects.
The Role of Exercise
Rapid weight loss is more about cutting calories than exercising. Talk with your provider about what type of exercise you should do while you are on this type of 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.
Who Might Benefit from a Very Low-Calorie Diet?
Very low-calorie diets are not OK for everyone. If your BMI is greater than 30, then very low-calorie diets are generally safe when used under proper medical supervision. For people who are overweight but not obese (BMI of 27-30), very low-calorie diets should be reserved for those who have weight-related medical problems and are under medical supervision. Losing as little as 5% of your body weight may improve medical conditions, including diabetes, high blood pressure, and high cholesterol.
A Study on Calorie Restriction
Published in final edited form as: Obesity (Silver Spring). 2013 Jun 13;21(12):2481-2487, a randomized trial examined the effects of prescribing 1,000 versus 1,500 kcal/day on 6- and 12- month weight losses in obese adults participating in lifestyle treatment for obesity. The primary aim was to determine whether assigning participants daily intake goals of 1,000 versus 1,500 kcal would result in differential weight reductions after 6 and 12 months of treatment. As body weight reductions of 5% or more decrease risk for diabetes and heart disease, their second aim was to assess whether assigning participants to 1,000 versus 1,500 kcal/day would result in differential percentages of participants achieving body weight reductions of 5% or more after 6 and 12 months of treatment. A final aim was to explore whether pretreatment caloric intake moderated the effects of prescribing 1,000 versus 1,500 kcal/day goals.
Participants were 125 obese women between the ages of 25 and 75 years who weighed between 91 and 136 kg and had BMIs between 30 and 45 kg/m2. Eligible participants were randomly assigned to intake goals of 1,000 or 1,500 kcal/day, respectively. Both dietary prescriptions were implemented within a standard behavioral lifestyle intervention for weight management that included two phases: Months 0-6 involved an initial treatment period of 24 weekly group sessions; Months 7-12 entailed an extended-care phase with six monthly group sessions.
From months 0 to 6, participants prescribed 1,000 kcal/day lost more weight than those prescribed 1,500 kcal/day (mean ± SE = −10.03 ± 0.92g vs. −6.23 ± 0.94 kg, P = 0.045); however, from months 7 through 12, only the 1,000 kcal/day condition experienced a significant weight regain (1.51 ± 0.77 kg, P ¼ 0.025). Baseline caloric consumption moderated the effect of treatment on regain; participants with baseline intakes ≥2,000 kcal/day who were assigned 1,000 kcal/day were significantly more susceptible to weight regain than those assigned 1,500 kcal/day (P = 0.049).
This randomized trial demonstrated four key findings. First, obese participants prescribed 1,000 kcal/day achieved significantly greater weight losses after 6 months of lifestyle treatment than those prescribed 1,500 kcal/day. Second, during extended-care treatment (months 7-12), the 1,000 kcal/day condition experienced significant weight regain, whereas the 1,500 kcal/day condition demonstrated no significant weight change. Third, baseline caloric consumption moderated the effect of treatment condition on weight regain.
Safe and Sustainable Weight Loss Strategies
People who want to reduce calories to lose weight should do so in small increments and avoid drastic changes. The best way to lose weight safely and successfully is by adopting healthy eating habits. Start with small, realistic goals, and then, as these become a habit, increase the goals. For example, make it a goal to start each dinner with a side salad or serve vegetables as a side dish. Once this becomes standard practice, introduce a second goal, such as having fruit with breakfast. Also, think about setting some exercise goals. A good example is setting a goal to walk for 15 minutes 3 times a week. Once this becomes routine, increase the time or number of sessions each week. Setting small goals and increasing them over time sets people up for success. Also, small goals are easy to implement and sustain.
Once you go off a diet, you need to change your lifestyle, committing to healthy eating and regular physical activity. Remember that it takes time to gain weight, so it may take even more time to lose weight safely. Quick weight-loss plans have little scientific support and can lead to individuals regaining all the weight they lost and more.