The prevalence of obesity has increased rapidly worldwide in recent years, posing serious health risks such as metabolic syndrome, non-alcoholic fatty liver disease, type 2 diabetes, and cardiovascular diseases. To combat obesity, a negative energy balance is crucial, where energy expenditure exceeds energy intake. While energy-restricted diets can achieve this, they often lead to post-loss weight regain due to increased hunger and decreased fullness. Furthermore, weight loss through energy restriction reduces both fat mass and fat-free mass (FFM), hindering continuous negative energy balance. For many people, weight loss can be frustrating, with numerous diets promising great results but varying greatly in effectiveness due to individual differences.
One such diet is the liquid diet, which promises rapid weight loss, such as 10 pounds in 2 weeks. Liquid diets are among the most restrictive eating plans, primarily consisting of soups, smoothies, or shakes. The basis of these diets for weight loss is reducing calorie intake, prompting the body to burn stored fat.
Understanding Liquid Diets
Liquid diets involve obtaining most or all daily calories from liquids instead of solid foods. These diets are very restrictive eating plans. Liquid diets can be categorized into several types:
Clear Liquid Diet: This diet is often prescribed by doctors for short periods, typically before a medical procedure or for digestive issues. It includes only clear liquids like water, apple juice, tea, and broth. This type of diet does not provide sufficient calories and nutrients and should only be followed under medical supervision for a short duration.
Full Liquid Diet: This diet is less restrictive than the clear liquid diet, allowing most beverages and foods that become liquid at room temperature, such as yogurt, popsicles, Jell-O, pudding, syrups, and some shakes.
Read also: Bikini Competition Prep Guide
Meal Replacement Liquid Diet: This involves substituting some or all meals with protein shakes, either store-bought or homemade. This can simplify weight loss by reducing the need for meal planning.
Detox Diets and Cleanses: These diets involve consuming specific juices or drinks that claim to remove toxins from the body. These diets often rely on a few natural ingredients like fruit and vegetable juices and may not provide all the necessary nutrients.
Very Low-Calorie Diets (VLCDs): These diets provide less than 1000 kcal/day, often using liquid formulas. They have been shown to reduce visceral fat and liver volume prior to abdominal surgery.
Potential Benefits of a Liquid Protein Diet
Weight Loss and Body Composition
Reduced Calorie Intake: Liquid diets can help reduce calorie intake, leading to weight loss as the body burns stored fat for energy. For weight loss, the basis of these diets is reducing your calorie intake. Unless you consume fewer calories than those you burn every day, the scale won’t move the way you want it to.
Increased Protein Intake: Several clinical trials have found that consuming more protein than the recommended dietary allowance not only reduces body weight (BW), but also enhances body composition by decreasing fat mass while preserving fat-free mass (FFM) in both low-calorie and standard-calorie diets. Protein is a component of the human body, a source of energy, and an essential nutrient that facilitates growth and development.
Read also: Transformations with Ozempic
Enhanced Satiety: High-protein diets (HPD) increase anorexigenic hormone levels (glucagon-like peptide-1, cholecystokinin, and peptide tyrosine-tyrosine) while decreasing orexigenic hormone levels (ghrelin), resulting in increased satiety signaling and, eventually, reduced food intake. One of the important mechanisms of HPD-induced satiety involves elevation of the anorexigenic hormones glucagon-like peptide- 1 (GLP-1), cholecystokinin (CCK), and peptide tyrosine-tyrosine (PYY). Release of GLP-1, CCK, and PYY is stimulated by proteins that also stimulate the vagus nerve, thus reducing food intake. Ghrelin is an orexigenic hormone that induces food intake by increasing hunger, and its plasma concentration is decreased by protein intake.
Increased Energy Expenditure: HPD increases energy expenditure through elevated diet-induced thermogenesis (DIT). The mechanism by which HPD increases energy expenditure involves two aspects: first, proteins have a markedly higher DIT than carbohydrates and fats. Second, protein intake prevents a decrease in FFM, which helps maintain resting energy expenditure despite weight loss.
Clinical Trial Evidence
Meta-Analysis Results: A meta-analysis of 24 randomized controlled trials (RCTs) comparing HPD and standard-protein diet (SPD) with isocaloric, energy-restricted diets showed that the HPD group had a significant reduction in BW, fat mass, and blood triglycerides, as well as a significant increase in FFM and resting energy expenditure (REE).
Long-Term Weight Loss: Fairly long-term clinical trials of 6-12 months reported that a high-protein diet (HPD) provides weight-loss effects and can prevent weight regain after weight loss. Westerterp-Plantenga et al. induced weight loss through a 4-week, very low-energy diet in 148 mildly obese participants, after which protein was additionally administered at 48.2 g/day for 3 months. The participants in the group given additional protein showed 50% less weight regain compared with control-group participants. Weight regain constituted FFM in the protein-group participants and fat mass in the controlgroup participants.
Additional Benefits
Reduced Liver Volume and Fat Content: Preoperative very low-calorie diets (VLCDs) have been shown to reduce liver volume and improve bariatric surgery safety. A study found that a 2-week VLCD led to a significant reduction in liver volume and liver fat content.
Read also: Dangers of the 800 Calorie Diet
Improved Metabolic Parameters: VLCDs lead to a significant decrease in body weight, reduction of liver volume, and improved parameters of inflammation, glucose, and lipid metabolism. In addition, hip/waist circumferences, body fat and fat-free mass decreased significantly. We found an increase of ALAT/ASAT and a significant decrease of triglycerides, LDL-cholesterol and HbA1c.
Potential Risks and Side Effects
Nutrient Deficiencies
Lack of Essential Nutrients: Restrictive liquid diets, especially clear liquid diets, may not provide all the necessary nutrients, leading to deficiencies if followed for too long. Liquid diets are low in protein and can make you lose a lot of lean muscle mass as you lose weight.
Fiber Deficiency: Liquid diets are often low in fiber, which can lead to constipation. A juice cleanse usually involves putting fruit and vegetables through a juicer and stripping them of their natural fiber. This fiber has many valuable and important functions such as removing LDL (low-density lipoprotein, aka the bad cholesterol) from your bloodstream, which helps in preventing high cholesterol, as well as aiding in digestion and preventing constipation.
Metabolic and Physical Side Effects
Slowed Metabolism: Drastically cutting calories can slow down metabolism as the body tries to conserve energy, potentially leading to weight regain after the diet. When you drastically cut calories, your metabolism slows to save energy.
Loss of Muscle Mass: Insufficient protein intake can lead to muscle loss. Liquid diets are low in protein and can make you lose a lot of lean muscle mass as you lose weight.
Side Effects of Water Fasting: Water fasts can cause headaches, fatigue, dizziness, bad breath, nausea, and constipation. If you’re going to do a water fast, you should be prepared for side effects such as headaches, fatigue, dizziness, bad breath, nausea, and constipation.
Dehydration: Drinking only water for a few days can lead to dehydration. About 20 to 30% of water is derived from foods you consume, as are most of your electrolytes.
Psychological and Behavioral Risks
Hunger and Deprivation: Liquids may not provide the same level of satiety as solid foods, leading to hunger pangs and difficulty sticking to the diet. It’s quite hard to ignore hunger pangs as liquids don’t fill you up as much as solid food does and it can be difficult to disregard the feeling of hunger.
Risk of Eating Disorders: Restrictive diets can trigger eating disorders such as anorexia, bulimia, and binge eating disorder (BED). Restrictive diets can trigger eating disorders such as anorexia, bulimia, and binge eating disorder (BED) (7).
Boredom and Fatigue: Consuming only liquids for days can lead to boredom and fatigue. You may feel tired or bored if you drink only liquids for days on end.
Concerns About Bone and Kidney Health
Bone Health: There have been concerns that HPD increases the resorption of bones by increasing the acid load in the body. However, a meta-analysis of 74 RCTs observed that subjects in the HPD group were not significantly different from low-protein-diet subjects with regard to bone mineral density of the lumbar spine and hips. Furthermore, low protein intake is generally considered a nutritional deficiency and has been described as a factor affecting osteoporosis development in older adults.
Kidney Health: There have also been concerns that HPD may deteriorate renal function by increasing the glomerular filtration rate (GFR) and inducing renal hypertrophy. However, studies have found no declining renal function in people with normal renal function. While HPD also does not affect renal function in healthy people, it can adversely affect renal function in people with kidney disease.
Factors to Consider Before Starting a Liquid Protein Diet
Individual Needs and Health Status
Consult a Healthcare Professional: It is essential to consult with a doctor or registered dietitian before starting a liquid diet, especially for individuals with chronic illnesses, pregnant or nursing women, and those taking insulin for diabetes. Before starting a liquid diet, speak with your doctor.
Nutritional Adequacy: Ensure that the liquid diet provides all the recommended vitamins and minerals. If you're considering one of the commercial diets, look at the daily values on the nutrition facts label. Be sure you're getting 100% of all the recommended vitamins and minerals.
Sustainability: Consider whether a liquid diet is a sustainable strategy for long-term weight management. Focusing on sustainable, long-term dietary changes is a better strategy.
Practical Considerations
Calorie and Macronutrient Balance: Calculate daily calorie needs based on individual factors such as weight, height, age, gender, and lifestyle.
Protein Intake: Aim for a protein intake of 1.07-1.60 g protein/kg BW/day (27%-35% of total energy intake consumed as protein) to preserve fat-free mass and enhance satiety.
Fiber Intake: Incorporate fiber sources to prevent constipation.
Pre-Bariatric Surgery
- Liver Volume Reduction: For individuals undergoing bariatric surgery, a 2-week liquid diet can reduce liver volume and improve surgical safety.
Guidelines for a 2-Week Liquid Protein Diet
Sample Meal Plan
- Breakfast: Protein shake (whey, casein, or plant-based) with added fruits and vegetables.
- Lunch: Blended soup with lean protein (chicken or fish) and vegetables.
- Dinner: Protein shake with healthy fats (avocado or nuts) and greens.
- Snacks: Small portions of yogurt, Jell-O, or clear broth.
Important Recommendations
Hydration: Drink at least 2 liters of calorie-free beverages daily. The patients have been instructed to drink 2 l calorie-free beverages daily.
Vegetable Intake: Consume 200-g low-starch vegetables per day. In addition to the diet products, an intake of 200-g low-starch vegetables per day was allowed in both groups.
Monitoring: Monitor for any adverse effects and adjust the diet as needed under medical supervision.