Calculate your Protein-Sparing Modified Fast macros based on lean body mass. Get your daily protein target, minimal fat and carb allowances, total calories, and exact portions of the best lean protein foods.
Essential fatty acids minimum
Fibrous vegetables only, aim for 0 net carbs
Hitting precise macros on PSMF is critical. BiteKit lets you log meals by speaking or typing — AI calculates the nutrition instantly.
A Protein-Sparing Modified Fast (PSMF) is one of the most aggressive fat-loss protocols in existence. It was originally developed in clinical settings in the 1970s to help severely obese patients lose fat rapidly while minimizing muscle loss. The core idea is elegantly simple: eat only the minimum calories needed to supply your muscles with amino acids, and let your body burn stored fat for almost all of its energy needs.
A PSMF day typically looks like this:
On a traditional deficit, protein needs are calculated relative to total body weight. On PSMF, protein is calculated relative to lean body mass (LBM) — because fat mass does not require protein to be maintained. Setting protein based on LBM ensures you are protecting every pound of metabolically active tissue without overshooting.
LBM (lbs) = Total Weight × (1 − Body Fat %)
Daily Protein (g) = LBM (lbs) × 1.5
Example: 180 lb person at 20% body fat → LBM = 144 lbs → Protein target = 216 g/day
The key criterion for PSMF-approved protein sources is the protein-to-fat ratio. You want foods that are almost entirely protein with trace amounts of fat, so the bulk of your calories comes from protein rather than fat.
~11 g protein per 100 g (liquid). Nearly zero fat. Versatile — scramble, make omelettes, or use as a binder. Avoid whole eggs; the yolk adds significant fat.
~18–20 g protein per 100 g cooked. Extremely low fat (under 2 g per 100 g). Bake, steam, or poach without added oil. Cod and tilapia are the leanest widely available options.
~24 g protein per 100 g cooked. Very low fat. Easy to prepare in large batches. Use without butter or oil — season with herbs and spices only.
~29 g protein per 100 g cooked. Exceptionally lean ground or sliced. Look for the "99% lean" label specifically — regular ground turkey is too high in fat for strict PSMF.
~12 g protein per 100 g. Look for 0% fat varieties. Easy to eat in large quantities and works well as a snack between meals. Contains some lactose, so count the carbs.
Because PSMF creates a deficit that can exceed 60–70% of TDEE, it is not sustainable long-term. The standard approach used in practice is:
2–6
Weeks maximum
Strict PSMF phase
1–2
Refeed days/week
For longer protocols
MD
Supervision required
Physician-guided only
During PSMF, electrolyte supplementation (sodium, potassium, magnesium) is critical because the rapid loss of glycogen and water also flushes minerals. Many practitioners also recommend a daily multivitamin. Monitor for symptoms of electrolyte imbalance — muscle cramps, heart palpitations, or extreme fatigue — and stop immediately if they occur.
| Approach | Protein | Fat | Carbs | Deficit |
|---|---|---|---|---|
| Standard deficit | Moderate | Moderate | Moderate | 300–500 kcal |
| Keto | Moderate | High | Very low | Varies |
| PSMF | Very high | Minimal | Near zero | 1000+ kcal |
PSMF is not a lifestyle diet. It is a short-term tool used strategically to accelerate fat loss before returning to a sustainable approach such as a standard calorie deficit or modified keto protocol.
A PSMF is an extreme low-calorie protocol that supplies only very lean protein, minimal fat (10–20 g/day), and near-zero carbohydrates. It is designed to maximize fat loss over a short period while preserving lean muscle mass.
The standard target is 1.5 g of protein per pound of lean body mass. This is higher than typical high-protein diets because it accounts for the extreme deficit and the need to provide all energy from protein rather than fat or carbohydrates.
LBM = Body Weight × (1 − Body Fat Fraction). For example, if you weigh 180 lbs at 20% body fat, your LBM is 144 lbs. You can enter your body fat percentage directly or use the Navy method estimation built into this calculator.
Only extremely lean protein sources: egg whites, cod, tilapia, shrimp, 99% lean turkey breast, and fat-free cottage cheese. Small amounts of fibrous, non-starchy vegetables are allowed. No oil, butter, nuts, seeds, or fatty cuts of meat.
PSMF should be limited to 2–6 weeks at a time under physician supervision. Longer periods increase the risk of electrolyte imbalances, micronutrient deficiencies, and other complications. A structured refeed period is required after each PSMF phase.
PSMF is not appropriate for people under 18, those with kidney or liver disease, insulin-dependent diabetics, people with heart conditions, anyone with a history of eating disorders, or pregnant/ breastfeeding women. Always consult a healthcare provider first.
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