Intermittent Fasting Calculator

Short-term time-restricted eating (16:8) combined with adequate protein intake (0.7 to 1.0 g per pound of body weight) and resistance training does not appear to cause more muscle loss than continuous caloric restriction. Very prolonged fasting without adequate protein does accelerate muscle catabolism. Resistance training during a fasting protocol is strongly recommended to preserve lean mass.

The body begins shifting from glucose to fat oxidation as glycogen stores deplete, typically between 12 and 18 hours into a fast depending on your activity level, diet composition in the preceding day, and individual metabolism. Measurable ketones in urine or blood typically appear after 14 to 18 hours of fasting for most people.

Yes, and many practitioners intentionally train in a fasted state to maximize fat oxidation. Fasted cardio and strength training are both practiced and generally well-tolerated after adaptation. However, high-intensity exercise may feel harder initially and electrolyte management becomes more important. Most research shows no meaningful difference in body composition between fasted and fed training over time.

Black coffee (no milk, cream, or sweeteners) contains roughly 0 to 5 calories per cup and does not measurably raise insulin or glucose. Most intermittent fasting practitioners and researchers consider it compatible with fasting for fat-loss and metabolic purposes. However, it does not maintain the autophagy-stimulating state in the same way as strict water-only fasting.