Alternate-day fasting works exactly as it sounds. Eat one day. Fast during the next one. Alternate throughout the week. Alternate-day fasting (ADF) is also known as the 4:3 diet because it goes on a 4:3 fast / eat rhythm week by week, like this: Just like other intermittent fasting methods, you can tailor ADF fasting to suit your needs — there's no universal how to do alternate-day fasting playbook.