The prevalence of adults with overweight or obesity represents an alarming public health challenge. Recent figures from the CDC show the majority of American society has become 'obesogenic,' characterized by environments that promote increased food intake, non-healthful foods, and low levels of physical inactivity. In light of these dieting trends, it is important to consider the risks of following a Kcal-restricted diet.
A very-low-calorie diet (VLCD), sometimes referred to as a semistarvation or crash diet, involves very low daily food energy consumption. Previous formulations of carbohydrate-free very low calorie diets provided 200-800 kcal/day and maintained protein intake but eliminated any carbohydrate intake and sometimes fat intake as well. Total diet replacement programs are the modern formulations regulated in Europe and Canada to ensure the recommended daily intake of necessary nutrients, vitamins, and electrolyte balance.
Understanding Very-Low-Calorie Diets (VLCDs)
Weight loss programs based on Kcalorie restriction are divided into two main categories: Low Calorie Diets (LCDs) and Very Low Kcalorie Diets (VLCDs). The primary difference is one of energy value, with VLCDs providing <800 Kcalories/d. VLCDs (i.e., Optifast and Medifast) have been used since the 1970s to induce rapid weight loss. They are often a treatment of choice for people who are more than 30% overweight with comorbidities and require the monitoring of a health professional. Many popular weight loss diets use 1,200 Kcal as the suggested Kcal minimum. This number derives from a scientific estimate of the lowest number of Kcalories required to deliver adequate nutrients.
What is a 500-Calorie Diet?
A 500-calorie diet is an extreme form of a very low-calorie diet (VLCD). The 500-calorie diet is an extremely strong and strict plan. It limits your daily calorie intake to an exceptionally low level, often replacing normal eating habits with liquid supplements, meal replacement products, or snack bars for a specific period. This method relies on meal replacements such as drinks, shakes, and pre-packaged foods to substitute at least two meals a day. This diet is also suitable for individuals who are severely overweight and have not succeeded in losing weight after trying multiple diet plans. With fewer calories, the body burns stored fat for energy, leading to fast weight loss. It is sometimes known as the 5:2 intermittent fasting plan, where calorie intake is restricted to 500 calories on two non-consecutive days each week while maintaining normal calorie consumption on the other five days. On fasting days, calorie intake typically covers only 20-25% of energy needs. Studies suggest that intermittent fasting may help overweight and obese individuals lose weight. However, findings remain inconclusive, and more research is needed to confirm these claims.
Potential Benefits of a 500-Calorie Diet
The benefit of the 500-calorie diet lies in its ability to promote rapid weight loss. Following this diet can enhance metabolism, accelerate fat oxidation, and support effective weight loss. This diet is often recommended for individuals who need to lose weight quickly to prevent potential health risks associated with excess weight. If you have a BMI over 30 (which your doctor will call “obese”), then 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. Losing as little as 5% of your body weight may improve medical conditions, including diabetes, high blood pressure, and high cholesterol.
Read also: Achieve Your Weight Loss Goals: 1700-Calorie Diet Explained
Comprehensive very-low-calorie diet (VLCD) programs are the preferred treatment for selected obese individuals. Typical VLCD patients have median body mass indexes of 36 kg/m2 and have median ages of 40 years. About 70% are female. Commonly associated medical problems include hypertension in 50%, hyperlipidemia in 41%, and diabetes mellitus or glucose intolerance in 14%. Typical weight loss with VLCD is around 21 kg in 16 wk. Reductions of 8-13% in blood pressure, 5-15% in serum total cholesterol, 5-20% in low-density lipoprotein-cholesterol, 15-50% in triglycerides, and decreases in blood glucose and glycohemoglobin in diabetic individuals accompany weight loss.
Risks and Side Effects
While the 500-calorie diet can aid in rapid weight loss, it is not suitable for everyone, as long-term adherence can lead to severe nutritional deficiencies.
Nutritional Deficiencies
The primary risk in taking in less than 1200 Kcal is nutrient deficiency. Theoretically, the delivery system for all nutrients (macro- and micro-) is food. When we decrease food intake below a certain amount, we are also decreasing all the nutrients that foods contain, risking deficiency. A study published in the Journal of Nutrition found that extremely low-calorie diets, such as the 500-calorie diet, can cause significant micronutrient deficiencies. The study revealed a significant decrease in levels of vitamin D, vitamin C, and zinc in obese individuals following the 500-calorie diet for more than 12 weeks. Most people cannot meet their nutritional needs with less than 1,200 calories daily. For example, according to the Mayo Clinic, a diet lacking zinc, found in pumpkin seeds and beef, may lead to hair loss. Low iron intake can cause anemia, while chronic deficiencies in calcium and vitamin D may result in osteoporosis later in life. Additionally, insufficient niacin, present in tuna and dates, could increase the risk of heart attacks due to arterial blockages. Therefore, it’s crucial to focus on the complete nutritional profile of the foods you eat, not just their calorie content.
Common Side Effects
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. Additionally, this diet may lead to side effects such as nausea, fatigue, diarrhea, increased sensitivity to temperature, menstrual irregularities, and hair loss. The lack of dietary fiber can also result in constipation. Furthermore, the immune system may be weakened, making the body more susceptible to various illnesses.
Muscle Loss
The 500-calorie diet can also put you at risk of muscle loss. Dr. Sharon Palmer, a nutritionist and author of Plant-Powered for Life, explains that "once your body has used up its fat reserves, it will also start burning healthy muscle." Initially, losing muscle may appear as rapid weight loss, but remember that not all body weight is bad. To maintain a healthy body, you need the ability to build and preserve muscle. A healthy diet burns fat, not muscle.
Read also: The Power of 100 Calories
Metabolic Changes
Another health risk to consider with the 500-calorie diet is how it affects the body’s metabolism. Prolonged calorie restriction significantly slows down the metabolism, causing the body to burn fewer calories over time. Additionally, as weight is lost, the body may require fewer calories to maintain the new weight compared to the original weight. Dr. Mindy Haar from the New York Institute of Technology’s School of Health said, "Many people believe they can stick to a restrictive diet for a short time, lose weight, and then return to their usual eating habits. However, doing so often results in regaining the weight until reaching the original level." Typically, weight loss includes both fat and lean mass, but when they regain weight is primarily fat, which can lead to increased long-term fat accumulation.
Gallstones
Gallstones are the most common serious side effect of very low-calorie diets. 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.
Cardiovascular Complications
Previous formulations (medical or commercial) of carbohydrate-free very low calorie diets provided 200-800 kcal/day and maintained protein intake, but eliminated any carbohydrate intake and sometimes fat intake as well. These diets subject the body to starvation and produce an average weekly weight loss of 1.5-2.5 kilograms (3.3-5.5 lb). However, the total lack of carbohydrates avoids protein sparing and thus produce a loss of lean muscle mass, as well as other adverse side effects such as increased risks of gout and electrolyte imbalances, and are thus disadvised.
Is Calorie Restriction Safe?
A low-calorie diet can be a safe, straightforward, research-confirmed path to weight loss. However, this slash-and-burn approach to calories may come with downsides. Meticulous tracking of numbers and portion sizes can create disordered eating behavior in some people. If you have a history of an eating disorder or a problematic relationship with food, it’s best to approach calorie counting with caution; enlist the help of a therapist or registered dietitian, if possible.
Regardless of your mental health history, a super-low-calorie diet may not be sustainable in the long term. We all need calories for survival. If your body senses it’s not getting enough, it will fight the process with a mechanism known as “starvation mode.” “Starvation mode is a defense mechanism that the body uses to prevent fat loss and starvation. The idea is, your body wants to use your fat to keep you alive, so you don’t burn as many calories,” says Felix Spiegel, MD, a bariatric surgeon at Memorial Hermann Medical Group in Houston. “This lowers your metabolic rate, which means you’re using less calories. If you cut back your calories too much, it hinders weight loss.” To prevent weight loss plateaus, Dr. Spiegel recommends a goal of 1 to 2 pounds lost per week.
Read also: Metabolism and Weight Loss
Who Should Avoid a 500-Calorie Diet?
Very low-calorie diets are not OK for everyone. Most people on very low calorie diets need vitamin and mineral supplements to ensure they are getting proper nutrition. Talk to your doctor to see if this kind of diet is appropriate for you. 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.
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.
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.
Important Considerations
Medical Supervision
Doctors may prescribe the 500-calorie diet if they determine that weight loss is necessary for your health. The decision whether to use it is based on the concern of the patient against the potential risks and complications. If a doctor doesn’t recommend this diet, you should not attempt it on your own. It requires close medical supervision. If your doctor hasn’t recommended a 500-calorie diet, you should not try this diet. A diet like this has risks and precautions associated with it. A doctor should supervise you while on this diet. VLCD-associated side effects can be managed medically without discontinuing treatment.
Long-Term Sustainability
While considerable short term success is reported with low- and very low-energy diets, the inescapable conclusion is that the programs that are effective in producing weight loss are not necessarily successful in producing long-term weight-loss maintenance. Additionally, for most people who are obese, obesity is a long-term condition that requires a lifetime of attention even after formal weight-loss treatment ends. Once you go off a diet, you need to change your lifestyle, committing to healthy eating and regular physical activity. Regaining weight is common following restrictive weight loss programs and most evidence suggests that the vast majority of people who lose weight regain it during the subsequent months or years.
Balanced Diet
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. One of the problems with a 500-calorie diet is that it places no limits on the fats and carbohydrates you consume. A serving of chocolate pound cake and a glass of milk adds up to about 500 calories. However, that so-called meal doesn’t even come close to giving you the nutrients you need, even if you’re just sitting in a meeting. Regardless of calorie count, a well-rounded diet includes fruits and vegetables, lean proteins, and whole grains. Being healthy is about a lot more than just a number.
Realistic Goals
Instead of basing your weight loss expectations on the 3500-calorie rule, use the National Institutes of Health’s free, online Body Weight Simulator to set more realistic goals. The simulator uses your height, current weight, sex and goal weight to estimate how much you should eat and how much weight loss you can expect over time. Reducing your usual calorie intake by about 500 calories a day is still a recommended strategy for many people. Find ways to do it that you can sustain long term. And the key message now is not to be discouraged or think it’s “not working” if your weight loss does not meet the now-outdated one-pound-per-week expectation.
Alternatives to a 500-Calorie Diet
Lifestyle Education
Lifestyle education promotes long-term weight maintenance of approximately 56% 2 yr after VLCD treatment.
Low Calorie Diets (LCDs)
These diets usually allow about 1,200 to 1,500 calories a day for women and 1,500 to 1,800 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 your 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. There are some studies that this method can cause rapid weight loss, but there is little information so far about whether the weight loss is sustained.
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. Diets that incorporate fasting can cause rapid weight loss.
Sustainable Changes
For cancer prevention and overall health, AICR promotes making small, everyday changes in diet and exercise as an effective way to lose weight. However, the extra physical activity and/or decrease in calories has to be permanent and it may take at least a year or more to reach your target weight. So choose changes you can stick with long-term (and be patient) rather than looking for quick fixes.