Not eating for 48 hours shifts your body from burning glucose to burning fat for fuel (ketosis), triggering cellular repair (autophagy), and potentially improving some metabolic markers like insulin sensitivity, but it can also cause hunger, fatigue, dizziness, and muscle loss, especially if done often or without proper hydration. Your body starts breaking down stored glycogen and then fat, while also beginning to cannibalize muscle for energy, though benefits like autophagy are peaking around this time, says Healthline.
Start small, keep it simple
The Benefits of Prolonged Fasting (48+ Hours)
Enhance Autophagy: Prolonged fasting triggers a more significant level of cellular cleanup and regeneration, which may help with aging and disease prevention. Reset Metabolism: Longer fasts can help break through metabolic plateaus and enhance insulin sensitivity.
DAY 3: The Results By the third day, many people experience something unexpected--mental clarity, reduced hunger, and a sense of lightness. Your body has adapted to using fat for fuel, insulin stays low, and energy levels often stabilize.
Studies show that it can take 20-48 hours for the body to shift into fat-burning ketosis mode. A 48-hour fast gives your digestive system a nice, cleansing rest and is just enough time for the body to start enjoying the benefits of ketosis. A 72-hour fast continues the benefits of the 48-hour fast.
Gut Health Revolution: Fasting doesn't just reset your digestive system; it enriches it. It promotes diversity in good gut bacteria and distributes them evenly throughout the gut.
Diarrhea following a fast most often relates to the meal you choose to break a fast. On the most basic level, eating too much or too quickly may upset your stomach, leading to diarrhea. This is the case even more so after extended fast periods.
At best, you may lose several pounds of water weight, but you won't lose a significant amount of fat in 2 days, regardless of your efforts. There are around 3,500 calories in one pound of fat. Quick calculations will tell you that you would need to burn 35,000 calories to achieve a 10-pound weight loss.
An occasional cheat meal will not make you gain weight as long as you consume it in moderation and maintain an active, healthy lifestyle. Weight fluctuations after a cheat meal are often due to water retention and temporary glycogen storage, not fat gain.
It won't lead to fat loss
While some people do this diet for the potential health benefits, many are attracted to fasting for three days as a way of losing weight. However, as previously mentioned, most of the weight loss is water weight and not fat loss.
The 3-3-3 rule for weight loss is a simple, habit-based method focusing on three key areas: 3 balanced meals a day, 3 bottles (or ~1.5L) of water by 3 PM, and 3 hours of physical activity per week, aiming for consistency over complex diets. It simplifies fat loss by establishing rhythm through consistent eating, adequate hydration to support metabolism, and regular movement, promoting sustainable health without intense calorie counting or restrictive rules, says Five Diamond Fitness and Wellness, Joon Medical Wellness & Aesthetics, and EatingWell.
The most immediate organ affected by a fast is the pancreas. During times of low plasma glucose, the pancreas will release more glucagon from the alpha cells found in the islets of Langerhans. Glucagon will mainly affect the liver as it stores most of the glycogen in the body.
Eating one meal a day can increase your blood pressure and cholesterol. This occurred in a group of healthy adults who switched to one meal a day to participate in a study. If you already have concerns in either area, eating just once a day might not be safe. Eating one meal late can cause your blood sugar to spike.
A single cheat day won't ruin your weight loss results, but multiple uncontrolled cheat days can have an impact. Don't see them as a chance to lose all self-control and binge eat. These actions can lead to serious food guilt and weight loss setbacks. It is important to do them in moderation.
What are the signs your body is in starvation mode?
The 2-2-2 food rule is a simple guideline for leftover safety: get cooked food into the fridge within 2 hours, eat it within 2 days, or freeze it for up to 2 months to prevent bacteria growth, keeping it out of the temperature "danger zone" (40-140°F or 5-60°C).
6 Ways To Get Back on Track After a Cheat
Fluid retention
The amount of fluid in your body changes throughout the day. It's totally normal for your weight to change up to four pounds in a single day, based on your fluid levels. Fluid retention, or edema, is when a lot of fluid builds up in the body. This can cause a sudden weight gain of 15 or more pounds.
If you're following a diet for weight loss, you may feel concerned about how overeating might impact your results, but one day of overeating will not negate the progress you've made. A small study from 2014 found that men who overate by 1,500 calories per day for three days did not experience any increase in fat mass.
Adele's significant weight loss wasn't from a quick fix but a two-year journey combining intense strength training, Pilates, hiking, boxing, and cardio, alongside major lifestyle changes focused on managing anxiety, not restrictive diets like the Sirtfood Diet, with workouts happening multiple times daily for mental and physical strength. Her routine included morning weights, afternoon hikes or boxing, and evening cardio, emphasizing getting stronger, which naturally led to fat loss and improved well-being.
You should step on the scale first thing in the morning. That's when you'll get your most accurate weight because your body has had the overnight hours to digest and process whatever you ate and drank the day before. And you should try to turn that step into a regular part of your routine.
Steps
Stool production is significantly reduced during long-term fasting.
Just like a fever that “burns off” invaders, diarrhea can be a way for the body to quickly flush the colon of unwanted toxins, bacteria, or waste. In essence, the body holds onto solid waste temporarily, while liquid waste is flushed out to clean up the digestive system.
Some people who follow a keto diet may experience diarrhea and other gastrointestinal (GI) problems as side effects.