PSMF Calculator
Calculate your Protein Sparing Modified Fast macros for rapid fat loss
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Medical Disclaimer: This calculator provides estimates for educational purposes only and does not constitute medical advice. Intermittent fasting is not appropriate for everyone. Do not fast if you are pregnant or breastfeeding, under 18 years of age, have a history of eating disorders, or have been diagnosed with Type 1 diabetes. If you take medications (especially insulin or blood pressure medication), have any chronic health conditions, or are recovering from surgery, consult your physician before beginning any fasting protocol. If you experience chest pain, fainting, persistent dizziness, or heart palpitations during a fast, stop immediately and seek medical attention.
How to Use the PSMF Calculator
- Enter your body composition — Input your weight, body fat percentage, and lean body mass. PSMF macros are calculated from lean mass to preserve muscle tissue.
- Set your deficit category — The calculator classifies you based on body fat percentage, as leaner individuals require shorter PSMF durations and different macro ratios.
- Review your macros — Get your daily protein target (typically 1.0 to 1.5 grams per pound of lean mass), minimal fat allowance, and near-zero carbohydrate limit.
- Check duration guidelines — The calculator recommends maximum PSMF duration based on your category, along with refeed frequency and diet break schedules.
Understanding Protein Sparing Modified Fasts
A Protein Sparing Modified Fast (PSMF) is an aggressive short-term dieting strategy that minimizes calorie intake while maintaining high protein consumption to preserve lean body mass. Originally developed in clinical settings for obese patients, the protocol typically provides 800 to 1,200 calories per day, almost entirely from protein sources like lean meat, fish, egg whites, and protein supplements.
The “protein sparing” component is critical. During severe calorie restriction, the body increases protein breakdown for gluconeogenesis (producing glucose from non-carbohydrate sources). By supplying adequate dietary protein, the PSMF reduces the body’s need to catabolize muscle tissue. Research by Dr. Lyle McDonald and clinical studies have demonstrated that well-constructed PSMFs can produce rapid fat loss of 4 to 7 pounds per week while preserving a significant portion of lean mass.
PSMFs are not appropriate for everyone and should be time-limited. Individuals with higher body fat can sustain the protocol longer (up to 12 weeks) because they have greater energy reserves. Leaner individuals (under 15% body fat for men, under 24% for women) should limit PSMF to 2 to 3 weeks with scheduled refeeds to prevent metabolic adaptation and hormonal disruption. Supplementation with a multivitamin, fish oil, and electrolytes is considered essential during PSMF.
Key Takeaways
- PSMF is a short-term rapid fat loss strategy, not a long-term diet. Duration should be limited based on starting body fat percentage.
- Protein intake is set high (1.0 to 1.5 g per pound of lean body mass) to minimize muscle loss during the aggressive deficit.
- Structured refeeds (planned high-carb days) are essential for leaner individuals to support thyroid function and leptin levels.
- Supplementation with electrolytes, a multivitamin, and omega-3 fatty acids is necessary to prevent nutrient deficiencies.
- Resistance training should continue during PSMF to provide a muscle-preservation stimulus, though volume may need to be reduced.
Frequently Asked Questions
How much weight can I expect to lose on a PSMF?
Fat loss typically ranges from 3 to 7 pounds per week depending on starting body fat and activity level. Initial weight loss may be higher due to water and glycogen depletion. Individuals with more body fat generally lose faster.
Is PSMF safe?
When properly structured with adequate protein, supplementation, and appropriate duration limits, PSMF has been used safely in clinical settings for decades. It is not recommended for individuals with eating disorder history, pregnant or nursing women, or those with kidney disease. Consulting a healthcare provider before starting is advisable.
Can I exercise during a PSMF?
Resistance training is recommended to preserve muscle mass, though you may need to reduce volume by 30 to 50 percent. High-intensity cardio should be minimized as energy levels will be low. Walking and light activity are appropriate for additional calorie expenditure.
What foods are allowed on a PSMF?
Primary food sources include chicken breast, white fish, lean turkey, egg whites, and low-fat cottage cheese. Non-starchy vegetables (spinach, broccoli, lettuce) are included for fiber and micronutrients. Cooking fats, oils, and caloric beverages are avoided.
How often should I do refeeds on a PSMF?
Refeed frequency depends on body fat category. Individuals above 25% body fat may not need refeeds for several weeks. Those between 15 and 25% should refeed every 1 to 2 weeks. Leaner individuals (under 15%) should include refeeds every 5 to 7 days to support hormonal balance.
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