Nutrition Diet: What is an example of a PSMF?

November 11, 2025 •

4 min read

In a study of obese patients, those following a PSMF lost an average of 31 pounds of body fat in just six weeks while preserving muscle mass. To understand what is an example of a PSMF, you must recognize it as a very low-calorie, high-protein approach designed for rapid, medically-supervised weight reduction.

Quick Summary

The Protein-Sparing Modified Fast (PSMF) is a very low-calorie diet that emphasizes high protein intake to preserve lean muscle while promoting rapid fat loss. It requires medical supervision and consists of an intensive, low-calorie phase followed by a refeeding phase.

Key Points

Intensive PSMF is <800 calories: The core of a PSMF is a very low-calorie phase, typically under 800 calories, lasting up to six months.
Example meal plan emphasizes lean protein: A typical PSMF meal plan includes lean protein sources like chicken, fish, or egg whites paired with non-starchy vegetables.
Medical supervision is essential: Due to its restrictive nature and potential risks, a PSMF should only be followed under the guidance of a healthcare professional.
Ketosis drives fat loss: The diet's extremely low carbohydrate content forces the body into ketosis, where it burns fat for fuel, preserving muscle mass.
Requires supplementation: To mitigate nutritional deficiencies and electrolyte imbalances, supplementation with multivitamins and minerals is necessary.
Success depends on the refeeding phase: Long-term weight maintenance is determined by the gradual reintroduction of carbohydrates and fats in the refeeding phase, accompanied by behavioral changes.

Understanding the Protein-Sparing Modified Fast

The Protein-Sparing Modified Fast (PSMF) is a highly restrictive dietary protocol first introduced in the 1970s for severely obese patients. Its name perfectly describes its function: a 'modified fast' that uses high protein intake to 'spare' the body's precious muscle tissue while forcing it to burn stored fat for energy. The body enters a state of ketosis, where fat is converted into ketones for fuel, which also helps suppress appetite. This process is different from other ketogenic diets, as the calories primarily come from lean protein rather than dietary fat. The PSMF is divided into two distinct phases: an intensive phase and a refeeding phase, both requiring close medical guidance.

The PSMF Intensive Phase: A Strict Approach

The intensive phase of the PSMF is the most restrictive period, lasting up to six months under medical supervision. During this time, daily calorie intake is severely limited to fewer than 800 calories. The macronutrient breakdown is strictly controlled, focusing on very high protein and minimal carbohydrates and fats. Protein intake is calculated based on your goal body weight, typically 1.2–1.5 grams per kilogram. Carbohydrate intake is kept extremely low (often below 20–50 grams) and comes solely from non-starchy vegetables. Added fats, such as oils and dressings, are not allowed. Due to the severe caloric restriction and elimination of food groups, a medically-supervised PSMF protocol includes essential vitamin and mineral supplementation, along with a recommendation for high fluid intake (at least 64 ounces of water daily) to prevent electrolyte imbalances.

What is an example of a PSMF meal plan?

A sample day on a PSMF emphasizes lean protein sources and non-starchy vegetables. The exact plan can vary, but the principles remain consistent. Here is a typical daily example:

Breakfast: Egg white scramble made with spinach and bell peppers.
Lunch: Grilled chicken breast served with a large side of steamed broccoli.
Dinner: Broiled cod filet alongside roasted asparagus spears.
Snack (if needed): A small portion of low-fat cottage cheese.

This simple structure highlights the diet's reliance on whole, nutrient-dense protein and vegetables. Processed foods, sweets, fruits, grains, and added fats are strictly prohibited.

The Refeeding Phase: Maintaining Progress

After the intensive phase, the 6-to-8-week refeeding phase begins, during which carbohydrates and fats are gradually reintroduced. This is a critical period for preventing rapid weight regain and transitioning to a more sustainable, balanced eating pattern. A doctor or dietitian will supervise this process, slowly increasing carb and fat intake while adjusting protein levels. Following the refeeding phase is crucial for long-term weight management and is often coupled with behavioral modifications and regular exercise.

PSMF vs. Traditional Ketogenic Diets

While the PSMF is a form of ketogenic diet, its macronutrient ratio is distinct. This comparison table highlights the key differences:


Feature	Protein-Sparing Modified Fast (PSMF)	Traditional Ketogenic Diet
Primary Calorie Source	Lean protein	Dietary fat
Calories	Very low, typically under 800 calories per day	Moderate, varies by individual needs
Carbohydrates	Very low, often under 20-50g per day from non-starchy vegetables	Very low, typically under 50g per day
Dietary Fat	Minimal, restricted to what is naturally in lean protein	High, comprising 70-80% of daily calories
Duration	Short-term (intensive phase up to 6 months)	Can be followed for longer periods
Medical Supervision	Required for safety due to low-calorie intake	Not always required, but often recommended
Primary Goal	Rapid weight loss with muscle preservation	Ketosis for various health or weight goals

Benefits and Risks of a PSMF Diet

Potential Benefits

Rapid Weight Loss: The PSMF is highly effective for quick, significant weight loss in obese individuals.
Muscle Mass Preservation: The high protein intake helps protect against the loss of lean muscle tissue, which is a common problem with traditional low-calorie diets.
Improved Health Markers: Studies show potential improvements in blood sugar control, blood pressure, and cholesterol levels, particularly in individuals with type 2 diabetes or hypertension.

Potential Risks and Side Effects

Nutritional Deficiencies: Due to its restrictive nature, the diet lacks many essential nutrients, necessitating supplementation.
Side Effects: Common side effects include fatigue, dizziness, headaches, constipation, and bad breath (known as 'keto flu' symptoms).
Electrolyte Imbalances: The combination of low calories and high fluid output can lead to serious electrolyte imbalances if not carefully managed with supplements and medical oversight.
Sustainability Issues: Many people find the diet difficult to maintain for extended periods, increasing the risk of weight regain after the intensive phase.
Risk for Certain Conditions: It is not suitable for individuals with certain health conditions, including severe kidney disease, liver failure, a history of eating disorders, or those who are pregnant or nursing.

Conclusion: A Tool for Supervised Weight Loss

The Protein-Sparing Modified Fast is a potent, short-term tool for rapid weight loss, primarily intended for obese individuals under strict medical supervision. What is an example of a PSMF is a diet consisting primarily of lean protein and non-starchy vegetables, designed to preserve muscle while burning fat stores. While it can deliver impressive initial results and improve certain health markers, it carries significant risks if not properly managed. Long-term success is highly dependent on adhering to the refeeding phase and adopting sustainable lifestyle changes, including diet and exercise. For anyone considering this path, the most important first step is consulting a doctor or registered dietitian to ensure it is a safe and appropriate option for their health needs.

Visit the Cleveland Clinic for more on medically supervised weight loss programs.

Frequently Asked Questions

On a PSMF, you can eat lean protein sources such as skinless chicken breast, fish (like cod and tilapia), egg whites, tofu, and very lean red meat. Non-starchy vegetables like leafy greens, broccoli, and asparagus are also allowed. All added fats, sugars, and starchy foods are typically avoided.

The intensive, very low-calorie phase of a PSMF is generally short-term, lasting up to six months. Following this is a crucial 6-to-8-week refeeding phase to transition back to a balanced diet and maintain weight loss.

No, while a PSMF does induce ketosis, it is different from a standard ketogenic diet. PSMF focuses on high protein intake as the primary calorie source, whereas a traditional keto diet is high in dietary fat.

The main risks include potential nutritional deficiencies, side effects like fatigue and headaches, and serious electrolyte imbalances if not medically supervised. It is also difficult to sustain long-term and carries a risk of weight regain.

Protein intake is high on a PSMF to protect against muscle loss during rapid weight reduction. In a very low-calorie state, the body needs protein to preserve lean muscle tissue rather than breaking it down for energy.

Yes, due to the extreme calorie and nutrient restriction, supplements are essential. A multivitamin, as well as potassium, calcium, magnesium, and sodium supplements, are typically recommended under medical supervision to prevent deficiencies and electrolyte issues.

No, PSMF is not safe for everyone. It is typically intended for obese adults and should be avoided by individuals who are pregnant, nursing, over 65, have certain health conditions, or have a BMI under 27.