Fat burning typically begins after approximately 12 hours of fasting and escalates between 16 and 24 hours of fasting.
Stage 2 (12-18 Hours): Partial to Full Ketosis
Depending on your last meal, you should be in full ketosis after about **16 to 18 hours** of fasting. If you had a high-carb meal, this stage might take a little longer to achieve. In Stage 2 of fasting, you start to switch into fat-burning mode.
Fasting for 16 hours a day, leaving an 8-hour eating window, is called the 16:8 method or the Leangains diet. Some experts may recommend females fast for 14 hours and slowly build their way up to 16 hours, while males can start fasting for 16 hours straight away.
Our data shows 20.7% of users opt for a 16-hour fast or more with a fat-burn rate of 42-46%. The 16:8 fasting ratio often involves skipping breakfast and not eating your first meal until midday.
For those aiming to lose belly fat, the 16/8 method is often recommended as the best intermittent fasting window to lose belly fat. By fasting for 16 hours and eating within an 8-hour window, you give your body enough time to burn stored fat while still allowing for a manageable eating period.
While both 12-hour and 16-hour fasting can promote fat burning, it's possible that a 16-hour fast may be more effective. This is because the longer fasting period may lead to a greater depletion of glycogen stores, which can trigger higher levels of fat burning.
You may need a longer or shorter eating window, or you may want to try out a new protocol entirely. Decrease (or increase) your calorie intake within your fasting window. Aim for 7–9 hours of sleep. Cut back on processed foods.
With intermittent fasting, breakfast is not only optional, it's discouraged. The most common method is a 16-hour overnight fast, followed by an 8-hour eating window. Yet, nutrition professionals have long suggested that breakfast is critical.
The lungs are the primary organ used to remove fat from your body. 1 During the energy-conversion process, fat leaves the body either as carbon dioxide when you exhale, or as water in the form of urine or sweat. 67 Body fat does not turn into muscle or exit the body through the colon.
Intermittent fasting can trigger ketosis, but only if you fast for at least 12 hours and potentially up to 18. It's also not the only way to stimulate ketosis — following a low-carb eating routine or extended periods of intense exercise can also trigger this fat-burning metabolic phase.
If you wake up every morning still burning mostly carbs, it's a sign your diet isn't optimized or you may have lost some metabolic flexibility, becoming dependent on sugars for energy.
18/6 intermittent fasting results: month 1
As the weeks go on, you may experience desirable benefits like noticeable weight loss and changes in body composition. You may notice a boost in mental clarity too.
Mostly, losing weight is an internal process. You will first lose hard fat that surrounds your organs like liver, kidneys and then you will start to lose soft fat like waistline and thigh fat. The fat loss from around the organs makes you leaner and stronger.
The human body can act as a fat-burning machine by depending on low-calorie foods instead of high-calorie foods in addition to doing regular exercise, avoiding toxins and processed food, and applying any fat flush dietary program under the approval of a professional doctor.
As fat cells shrink, the surrounding tissue doesn't always tighten up right away. Combined with loose skin, this can make areas like the belly or thighs feel softer and jiggly. The good news? This phase is temporary.