Your body may go into ketosis after just 12 hours of not eating, which many people do overnight before they "break fast" with a morning meal. (A midnight snack obviously sabotages this process.) A keto diet keeps you in ketosis for much longer time periods because you avoid carbohydrates, which supply glucose.
If you don't eat for 10–16 hours, your body will go to its fat stores for energy, and fatty acids called ketones will be released into the bloodstream. This has been shown to protect memory and learning functionality, says Mattson, as well as slow disease processes in the brain.
Additionally, it will take your body a while to get used to this new eating schedule. So don't expect results right away. You may need to wait between 2 and 4 weeks to see or feel any results.
In order to enter the autophagy phase through intermittent fasting, you need to fast for a minimum of 14 to 16 hours. A research review found that intermittent fasting and autophagy can make cancer treatments more effective while protecting normal cells and reducing the side effects.
Both 12-hour fasting and 16-hour fasting can be effective for weight loss, but 16-hour fasting may be more effective because it may lead to a greater reduction in overall caloric intake (through a more condensed eating window) and promote more significant reliance on fat burning.
The rules for this diet are simple. A person needs to decide on and adhere to a 12-hour fasting window every day. According to some researchers, fasting for 10–16 hours can cause the body to turn its fat stores into energy, which releases ketones into the bloodstream. This should encourage weight loss.
For example, studies have found that people who regularly fast more than 16 or 18 hours a day have a higher risk of gallstones. They're also more likely to need surgery to remove the gallbladder. Eating for 12 hours and then fasting for 12 hours is likely safe for most people, Longo explains.
In immediate periods of ketosis, a person may experience increased thirst, muscle cramps, and headaches. Ketosis is a metabolic process that occurs when the body begins to burn fat for energy because it does not have enough carbohydrates to burn. During this process, the liver produces chemicals called ketones.
The easiest and fastest way to get into ketosis is by fasting and exercising. Fasting allows the body to burn its stored glucose essentially forcing it to create a new type of fuel called ketone bodies. Exercise on the other hand also helps to burn glucose.
Fat burning typically begins after approximately 12 hours of fasting and escalates between 16 and 24 hours of fasting.
Generally speaking, ketosis can be achieved by fasting for longer than 72 hours (3 days) (2) or by following a very low carb (30-50g/day), keto diet for up to several weeks. Below are some key timeline benchmarks. During this phase, your body is no longer using stored carbohydrates for energy.
Caloric Deficit and Weight Loss
Studies show that, on average, intermittent fasting can lead to a weight loss rate of approximately 0.55 to 1.65 pounds (0.25–0.75 kg) per week, accompanied by a noticeable reduction in waist circumference, indicating a decrease in belly fat.
16-20 hours
Our data shows 20.7% of users opt for a longer fast of 16 hours or more with a fat burn rate of 42-46%. The 16:8 ratio often involves skipping breakfast and not eating your first meal until around midday.
Whole grains like quinoa and oats can be good to eat after fasting. Quinoa is a complete source of protein, rich in fiber, and naturally gluten-free. Oats and oatmeal can also be nourishing, filling, and not particularly hard to digest.
You will generally experience more fat burning with a 16 vs 12 hour fast because the longer fasting duration allows you to burn through more of your glycogen stores. This is a crucial first step before significant fat burning and ketosis can set in.
In the case of Intermittent fasting, skipping your dinner is better and easier. You can have your dinner either early or have a heavy snack and can begin your fasting. Research suggests that fasting in the evening and overnight, then eating early in the morning is the better way to follow this diet to lose weight.
Animal studies have shown evidence of autophagy after 24 hours of fasting, which starts peaking at around 48 hours of fasting. Some studies have detected autophagy in human cultured neutrophils (the most abundant type of immune cell in the blood) after 24 hours.
In addition, fasting activates autophagy - which is a process that kicks off a series of biological changes that rejuvenate your cells. Weaker mitochondria die and new, stronger ones take their place - think of it as a spring-cleaning for your body!