Quick answer: Eat 0.7–1g of protein per pound of body weight per day during intermittent fasting to preserve muscle mass. If you are resistance training, target 1–1.2g per pound. Split this across your eating window in 2–3 meals with 30–50g of protein each.

How Much Protein During Intermittent Fasting: Targets, Timing, and Sources

Intermittent fasting compresses your eating into 6–10 hours. What you choose to eat in that window determines whether you lose fat and preserve muscle — or lose both. Protein is the variable that separates those two outcomes.

Most people doing IF underestimate how much protein they need and overestimate how much they are getting. The consequences show up 2–3 months in: the scale has moved, but so has muscle. Strength decreases. Metabolism slows. Results plateau. The fix is almost always the same: hit your protein target.

Why Protein Matters More During IF (Not Less)

A common misconception is that because you are eating less frequently, protein requirements go down. The opposite is true, for two reasons.

First, muscle protein synthesis has a timing component. Your body can only use roughly 30–40g of protein for muscle synthesis in a single sitting before the rate-limiting enzymes (specifically, mTOR pathway activation) reach saturation. Protein above that amount in one meal is still digested and metabolized, but its contribution to muscle preservation is reduced compared to spreading the same total across multiple meals.

When you compress your eating to 16:8 or tighter, you have fewer meals to distribute your protein across. This means each meal needs to be intentionally designed to hit that 30–40g mark — and you need to make sure you are actually reaching your total daily target, because a compressed window makes it easy to fall short without realizing it.

Second, fasting elevates gluconeogenesis. During extended fasts, your liver produces glucose from non-carbohydrate sources — primarily amino acids drawn from muscle tissue. This process increases when protein intake is insufficient. Higher dietary protein gives your body a readily available amino acid pool so it prioritizes dietary protein over muscle tissue for gluconeogenesis.

Research confirms this. A 2020 meta-analysis in Nutrients found that higher protein intake during caloric restriction (>1.2g/kg) significantly attenuated muscle loss compared to standard protein intake, with the effect size larger in protocols involving extended fasting windows.

Protein Targets by Goal

Baseline for fat loss with muscle preservation: 0.7–1g per pound of body weight per day (approximately 1.6–2.2g/kg)

For a 160 lb person: 112–160g of protein per day

If you are resistance training (3+ days/week): 1–1.2g per pound of body weight per day

For a 160 lb person: 160–192g of protein per day

If you are older than 50: Add 10–20% to either target. Anabolic resistance — the reduced efficiency of muscle protein synthesis in response to dietary protein — increases with age, meaning you need more protein to achieve the same muscle-preserving effect.

If you are doing OMAD or an 18:6 window: Your protein target does not decrease because your eating window is shorter. But hitting 150+ grams of protein in one or two meals becomes logistically difficult and often unpleasant. This is one practical reason why very compressed eating windows are harder to sustain — not just hunger, but nutrient adequacy.

Protein Timing Within Your Eating Window

For a standard 16:8 window (noon to 8pm), a practical protein distribution looks like this:

Noon — First meal (break fast): 35–45g protein

6 oz chicken breast, Greek yogurt, eggs, or protein shake + eggs

3–4pm — Mid-window meal or snack: 20–30g protein

Cottage cheese, tuna, hard-boiled eggs, protein shake

7–8pm — Final meal: 35–45g protein

Salmon, lean beef, shrimp, tofu with a protein-dense side

This structure hits 90–120g without heroic effort. If your target is higher (150–190g for larger or highly active individuals), increase portions at each meal and add a protein-focused snack.

Should you prioritize protein in your first meal or last? Both matter, but if you are resistance training, prioritize getting 40g+ of protein in the meal closest to your workout — either pre or post-training. Research on the "anabolic window" has become less precise over the years, but getting protein within 2 hours of a strength session remains a reliable practice for muscle protein synthesis.

Best Protein Sources for IF

The best protein sources during an intermittent fasting eating window share two qualities: high protein density (grams of protein per calorie) and relatively fast digestion (to maximize absorption in a compressed window).

Animal proteins (highest quality):

Chicken breast: 31g protein per 4oz, minimal fat
Canned tuna: 25g protein per 3oz, extremely convenient
Greek yogurt (2% or full fat): 17–20g per cup, portable
Eggs: 6g per egg — pair with 3–4 eggs to hit useful amounts
Cottage cheese: 25g per cup, high in casein (slow-digesting, good for final meal)
Salmon: 25g per 4oz, plus omega-3s that support inflammation reduction
Lean beef (90/10 or leaner): 22g per 3oz

Plant proteins:

Tempeh: 20g per 4oz — highest protein plant source, complete amino acid profile
Edamame: 17g per cup
Lentils: 18g per cup cooked — high in fiber, pairs well with satiety
Tofu: 10g per 4oz — combine with other sources

Protein supplements: Whey protein isolate (25–30g per scoop) is a practical tool for hitting targets in a compressed window. It is not mandatory, but it makes the math easier. A shake during your eating window is not "cheating" — it is a food.

What Happens When You Skip Protein

The scenario: you are doing 16:8, eating salads and light meals, the scale is dropping. You feel like it is working.

By month 2, you notice that you are weaker in the gym. Your waist is smaller but so are your arms. You have lost 12 lbs — but a DEXA scan or body fat measurement reveals 4 lbs of that was muscle. Your resting metabolic rate has dropped proportionally.

This is the most common mistake in intermittent fasting and the reason the Fasted app includes protein tracking alongside fasting windows. Monitoring both together is what separates effective fat loss from simply losing weight.

For more on what to eat during your eating window, see best foods for intermittent fasting and intermittent fasting and muscle preservation.

FAQ

Q: Can I eat all my protein in one meal during IF? A: You can, but it is not optimal. Muscle protein synthesis uses roughly 30–40g per sitting efficiently. Spreading protein across 2–3 meals in your eating window makes better use of what you eat. Very high single-meal protein amounts (80g+) are not harmful, just less efficient for muscle preservation.

Q: Does protein break a fast? A: Yes. Protein — like any macronutrient — triggers an insulin response and ends the fasted state. Eat protein within your eating window, not during the fasting hours.

Q: Should I take protein powder while intermittent fasting? A: Use it if it helps you hit your daily protein target. Whey or plant-based protein powder during your eating window is nutritionally equivalent to food protein. Some people find shakes easier than eating enough whole-food protein in a compressed window.

Q: How do I know if I'm eating enough protein? A: Track for 3–5 days using a food logging app. Most people are surprised to find they are hitting 60–80g when they think they are eating "a lot" of protein. The target is 0.7–1g per pound of body weight — a number most people underestimate significantly.