Rapid weight loss diets, characterized by losing more than 2 pounds (1 kg) per week, are often sought by individuals with obesity aiming for quick results. While these diets can offer certain benefits, they also pose significant risks. This article explores the various types of aggressive weight loss plans, their potential advantages, and the associated dangers, providing a comprehensive overview for those considering such approaches.
Understanding Rapid Weight Loss Diets
A rapid weight loss diet is a type of diet in which you lose more than 2 pounds (lb) or 1 kilogram (kg) a week over several weeks. To lose weight this quickly, you must eat very few calories. These diets are most often chosen by people with obesity who want to lose weight quickly. People on these diets should be followed closely by their 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.
Types of Rapid Weight Loss Diets
Several types of diets fall under the umbrella of rapid weight loss strategies, each with its own approach and level of intensity.
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 1,200 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.
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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.
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. For most people, it is safest to choose a diet in which you lose a 1/2 to 1 lb or 225 to 500 grams (g) a week.
Potential Benefits of Rapid Weight Loss
Rapid weight loss diet is usually for people who have health problems because of obesity. For these people, losing a lot of weight quickly can help improve:
- Diabetes
- High cholesterol
- High blood pressure
For those who have decided to undergo bariatric surgery, the gold standard protocol is to undergo a very low-calorie diet (VLCD) for 2-4 weeks prior to the surgery. The reason this is often performed is to reduce the size of the liver prior to surgery.
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Risks and Side Effects
You should only follow one of these diets with the help of your provider. Losing more than 1 or 2 lb (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
- 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.
Specific Diet Plans and Their Implications
Ketogenic Diet
The ketogenic diet, popularized in the 1920s, involves restricting carbohydrate intake to <50 g daily This diet is often used by individuals wishing to lose weight rapidly in the short term, with some reports of people losing up to 9.9 pounds (4.5 kg) in 2 weeks and up to 57.3 pounds (26 kg) if maintained over 2 years. Risks include vitamin and mineral deficiencies. For individuals undergoing a 12-week ketogenic diet, magnesium, calcium, iron, phosphorus, and potassium levels were found to be less than the recommended values. Although this was not evident in serum levels at the end of the study, it could indicate deficiencies if the ketogenic diet were extended beyond those 12 weeks. Hypercalciuria and renal stones have also been reported as long-term adverse effects of the diet. Short-term risks include gastrointestinal effects such as nausea, vomiting, and decreased energy.
Atkins Diet
The Atkins diet, created in the 1960s, is similar to the ketogenic diet, restricting carbohydrates and promoting increased fats and proteins. However, it differs in that it slowly increases carbohydrates through different program phases. The first 2 weeks of the diet constitute an induction phase, with <20 g of carbohydrates consumed daily (even less than the ketogenic diet).
Paleo Diet
The paleolithic diet, introduced in the 1980s, focuses on eliminating processed foods and only consuming lean meats, fruits, nonstarchy vegetables, nuts, and seeds while restricting dairy products. Individuals adhering to this diet over 12 weeks were found to have weight loss as high as 4% to 6% of their starting body weight. There is limited research regarding long-term adherence and sustainability.
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Intermittent Fasting
Intermittent fasting, thought to improve metabolic and glycemic control, is defined as abstinence from food for a given amount of time followed by a meal. Rapid weight loss, induced by intense dieting, extreme exercise, fluid restriction, medication use, or fasting without electrolyte supplementation, can lead to a series of adverse effects with electrolyte derangements, decreased athletic performance, hormone imbalance, and potential organ damage. Intermittent and long-term fasting can result in sodium, potassium, and uric acid imbalances due to fluid shifts, reduced electrolytes, and reduced water uptake. These shifts are typically transient, and electrolyte levels tend to normalize once the body reestablishes fluid balance.
The South Beach Diet
Like Dr. Atkins, Dr. Arthur Agatston was a cardiologist interested in helping his patients lose weight sustainably without feeling hungry. He liked certain aspects of the Atkins diet, but was concerned that unrestricted use of saturated fat might increase the risk of heart disease. Therefore, in the mid-1990s, he created a lower-carb, lower-fat, high protein diet called the South Beach Diet, named for the area in South Florida where he practiced medicine. Although Stage 1 of the diet is low in carbs and very low in fat, the diet becomes less restrictive in Phases 2 and 3, which allow limited quantities of all types of unprocessed foods while keeping protein intake high.
The 5:2 Diet
The 5:2 diet is a type of intermittent fasting, also known as alternate-day fasting. On this diet, you eat as you usually would for five days a week and restrict your calorie intake to 500 to 600 calories for two days each week, resulting in an overall calorie deficit that leads to weight loss. The 5:2 diet is considered a form of modified alternate-day fasting. By contrast, some types of alternate-day fasting involve going without food for a full 24 hours.
Vegan Diet
A vegan diet does not include animal-based products like meat, poultry, fish, or foods derived from animals like dairy or eggs. Itâs important to note that vegan diets can vary widely and may be balanced or unbalanced, depending on the types of foods they contain. However, research suggests that whole plant-based vegan diets may support weight loss. They may also have additional benefits, including helping prevent and manage chronic diseases, such as type 2 diabetes and hypertension, supporting the gut microbiome (the healthy bacteria that live in the digestive tract), and improving blood glucose levels.
Weight Cycling and Metabolic Rate
Homeostasis occurs in each human body at a different level of weight. Each person has a resting metabolic rate, defined as the rate of energy production and expenditure needed to function while at rest. After weight loss, the resting metabolic rate slows, likely to counter weight loss and return to homeostasis. It is hypothesized that due to this phenomenon of "metabolic adaptation," weight regain is likely even after weight is lost.
Weight cycling, or yo-yo dieting, is a vicious cycle of weight loss and regain that permanently slows metabolic rate. The metabolic rate measures the number of calories needed for breathing, digestion, maintaining body temperature and other basic body functions. It accounts for 70% of calories needed per day.
Hormonal Imbalances
Alterations in body mass can cause a shift in homeostasis, influencing the delicate balance of anorexogenic and orexigenic hormones that regulate satiety and hunger. This can lead to changes in the body's ability to sense satiety. Anorexogenic hormones, such as leptin, peptide YY, and cholecystokinin, play a crucial role in signaling satiety, communicating to the brain that the body does not require additional calories. Orexigenic hormones, like ghrelin, stimulate hunger. During dieting and caloric restriction periods, orexigenic hormones increase, and anorexogenic hormone levels decrease. Even after weight loss, the drive to eat remains heightened, potentially indicating the risk of weight regain. Hormone levels may never revert to their pre-dieting states. These ongoing hormonal imbalances increase individuals' challenges in maintaining long-term weight loss. Thyroid hormones, T3 and T4, have been identified as contributors to weight loss, with medications and supplements targeting thyroid hormones becoming another method utilized.
The Role of Medications
Medications, including orlistat, phentermine and topiramate, naltrexone and bupropion, liraglutide, and semaglutide, have obtained FDA approval for weight loss in the United States, and all are effective for weight loss. FDA guidelines recommend that consideration for these medications include a body mass index (BMI) >30 or ranging from 27 to 30 with an obesity-related comorbidity (type 2 diabetes, hypertension, or any other disease secondary to obesity). When weight loss medications are considered, individuals should be educated that they will likely be on anti-obesity medicines for life, as obesity is a chronic disease, often relapsing if pharmacotherapy is ceased. Despite weight loss medications effectively causing >5% body weight loss in most individuals, undesirable adverse effects are common.
Bariatric Surgery
Bariatric surgery, coming into existence in the 1950s, has become a method for rapid weight reduction exceeding 20% of total body mass in some cases. The 2 most common bariatric surgeries performed worldwide are the sleeve gastrectomy and the gastric bypass. Aside from immediate postoperative complications, chronic long-term complications include nutrient deficiencies secondary to anatomical changes that can be present for life. Iron, vitamin B12, copper, and calcium malabsorption after gastric bypass likely occur due to bypassing the duodenum and proximal jejunum, where much of the absorption occurs. Dumping syndrome (accelerated gastric emptying after meals) has also been reported amongst bariatric patients, especially those with gastric bypass, with resolution usually by 2 years postsurgery.
Aggressive Dieting: Nuances and Considerations
Aggressive dieting does not really have a definition. The general concept just involves aiming for relatively quick weight loss. As a simplified rule, aiming for >1kg per week weight loss, for multiple weeks in a row, is aggressive dieting. It is worth acknowledging that the habits required to be in a moderate calorie deficit are different to the habits required at maintenance calories. Weight-loss maintenance has less to do with what you do during the weight loss phase, and more to do with what you do AFTER the weight loss.
Downsides
There are a lot of downsides to aggressive dieting, including:
- Increased hunger
- Increased restriction
- Increased risk of muscle loss
- Potential increased risk of disordered eating
- Difficulty adhering to the plan
- Harder to get a good amount of micronutrients from food
- Reduced enjoyment of food and social situations
- Decreased performance in training and competitions
- Low energy availability and downregulation of certain processes of the body
Potential Benefits
The benefits basically come down to two things:
- Time
- Adherence (in some cases)
Who Should Avoid Aggressive Diets?
People with a history of disordered eating should not do this approach. Even if the disordered eating was not recent, the risk is still quite high. The other group to highlight is those who have tried aggressive diets more than once without success.
The Importance of a Balanced Approach
Instead of resorting to extreme diets the key to successful weight management is a balanced lifestyle approach. Focus on improving your lifestyle with a healthy balanced dietary plan, regular physical activity, stress reduction and good sleep patterns along with a good support system.
Practical Summary
Aggressive diets should be used infrequently, and most people should not use them at all. If youâre considering an aggressive diet, it makes sense to first determine whether youâre a good fit for that approach. Itâs also important to ensure youâre in a strong starting position before beginning. It is helpful to have an end date for the diet as well as a plan to transition out of the approach.