Intermittent fasting

Intermittent fasting is an eating pattern that alternates fasting periods with eating windows, focusing on when a client eats rather than what they eat.^{1International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 476.},^{2International Sports Sciences Association, Fast Track Study Guide: Nutrition, p. 10.} Common versions include 16:8 (a 16-hour fast and an 8-hour eating window), 5:2 (cutting calories on two days each week) and alternate-day fasting.^{1International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 476.},^{2International Sports Sciences Association, Fast Track Study Guide: Nutrition, p. 10.}

Fasting helps some clients maintain a calorie deficit for fat loss.^{1International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 476.} It doesn’t raise metabolism or produce more fat loss than conventional dieting when weekly calories are matched.^{3Norton and Baxter, The Complete Reverse Dieting Guide, p. 75.} The IPTA textbook describes weight-loss research as promising but inconclusive overall, with possible improvements in insulin sensitivity and blood pressure.^{1International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 476.}

In practice

Suitability varies: Baxter prefers an 8 to 10 hour eating window for bigger, more satisfying meals, while Norton finds fasting makes him so hungry that he eats more.^{4Norton and Baxter, The Complete Reverse Dieting Guide, p. 38.}

Watch for dizziness, weakness and headaches; longer fasts also lead some clients to overeat.^{1International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 476.} Muscle gain is still possible: in an 8-week supervised study, trained women gained similar fat-free mass and muscle whether they ate throughout the day or within an 8-hour window.^{5Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 234.}