Fasting regimes promise a ‘10-pound loss in just three days!’ – but do these claims have any basis in fact? Here’s a reality check on a 72-hour water fast, covering exactly what happens during such a fasting regime, actual weight loss, and kinds of weight shed, myths, facts, and how you can make a safer fast if you do go for a short fast.
What your body is doing during a 3-day water fast
Timeline:
0-11 hours: “The glucose in your last meal and your blood sugar supply will be used up. Insulin levels will drop, and glycogen will begin to break down in your liver and muscles.”
11-24 hours: “Now your liver glycogen will become your primary energy source. About 18 to 24 hours into your fast, your liver glycogen will be depleted, and your body will switch to burning fat for fuel and producing ketones. This process is when people say they enter ketosis. ”
24-72 hours: “Fat and ketone production will increase, and your brain will begin using ketones for fuel. Some muscle tissue will be broken down for energy, especially if you haven’t eaten protein for a long time. Stress hormones such as cortisol will become elevated.”
How Much Weight Will Actually Come Off?
A weight loss of 1-4kg or 2-9lbs can be expected in most people after 3 days, but this is mainly water and glycogen.
Why:
Glycogen and water. One part glycogen holds about 3-4 parts water. As a person starts using glycogen on the first day, they see a tremendous amount of weight loss, which is basically due to water. Research studies and calculations about short fasting/ ketogenic Diet transitions have unveiled a major portion of early weight loss being due to water and not fat. Calorie deficit calculations.
One pound or 0.45 kg of fat = 3,500 kcal of storage. A normal individual’s expenditure level can vary from 1,800-2,500 kcal; hence, without food intake for three days, they will have an expenditure of ~5,400-7,500 kcal, theoretically making it a 1.5-2.1 lb or 0.7-1.0 kg net loss in pure fat, if achieved solely from glycogen stores. As a fact, it will come from other sources too. Variations in individual calculations. Heavy people with higher glycogen content and water will have a substantial scale loss in this time span. Activity level, drugs, menstrual cycles, salt intake, and variation in carbon storage will adjust this figure. Variations have been widely observed in studies about fasting therapy.
What this means in practical terms is a reasonable expectation of seeing 2–6 pounds (1–3 kilograms) lost on the scale by day three, with a smaller portion, perhaps .5–2 pounds (0.25–1 kilogram) of this being actual fat, and the remainder being water and a bit of muscle.
Myths vs. Reality
Legend: “You will shed 10 pounds of fat in three days.”
Fact: That’s simply not possible for a healthy individual. Short-term fasting will have lost basically water/glycogen, not fat. Actual fat loss is limited by energy calculations.
Legend: “Fasting will boost your metabolism.”
Fact: Metabolic rate slows a bit when calorie restriction is prolonged, and short fasts induce a hormonal response, such as lowered insulin and elevated cortisol, but do not induce a dramatic increase in calorie burning above usual resting levels.
Three days of fasting fix everything
Fact: Fasting for a short period can impact metabolic function, leading to increased levels of ketones and autophagy, but claims about fasting for 72 hours about “resetting” hormones, digestion, or immunity are not proven and border on pseudoscience claims.
Possible benefits (reported by people, research findings): Rapid loss of excess water/polyglylic acid. Initial improvements in insulin sensitivity in a few studies conducted on fasting regimes (but this must be considered in context and timeframes). Increased production of ketones and a switch in metabolism towards burning fat, with some subjects noting a suppression of appetite after day one.
Real dangers and safety issues:
- Dizziness
- hypoglycemia
- passing out
- headaches
- dehydration
- electrolyte imbalance
- Muscle tissue loss
A small amount of this will be lost, especially if you do not consume proteins or work out your muscles during fasting phases. After a series of fasting phases, this starts being very relevant. Drug interaction dangers. Diabetes, blood pressure, and anticoagulant medicines can become life-threatening if you fast.
Advice: always ask a medical professional if you are taking prescribed drugs. Risk of eating disorders. Fasting can provoke an eating disorder in vulnerable subjects. No fasting for most people. Pregnant, nursing, children, elderly, underweight subjects, and people with chronic illnesses shouldn’t attempt a water fast.
Alternative methods: But if your aims are fat loss or health benefit, then studies support calorie restriction daily, a high-protein diet, resistance exercises, and a reliable method of intermittent fasting, such as time-restricted fasting or brief fasts of 24 to 48 hours, rather than water fasting periodically.
Actions if Considering a 3-Day Fast
Communicate with your healthcare provider before fasting, especially if taking medication or having any chronic health issues.
Stay hydrated & balance electrolytes:
- Drink water all day, and if fasting over 24 hours, think about an electrolyte supplement (common ones include salt & potassium).
- No heavy exercise during fasting; Light walking or mobility exercises are alright, but resistance training when you’re eating to spare your muscles.
- Gradually begin to re-feed when fasting ends, over a span of 24-48 hours with nutritious food intake, including a balance of protein, carbohydrates, & fats.
- Closely follow bodily reactions; discontinue fasting if experiencing light-headed sensations, dizzy spells, racing heart, & confusion.
Experimental fasting, not a common habit:
Fasting may have a medical application occasionally, but a common “detox” fast can do more harm than good in facilitating a healthy technique for weight control.
Conclusion
A 3-day water fast will definitely give you a good amount of weight loss, which will be evident in the form of a substantial drop in your scale reading, with a loss of 1-4 kg (2-9 lb) at least in a short span of time, but this will be largely in the form of glycogen depletion in your body. Losing fat in a 72-hour fast is not very feasible, but this will come with side effects such as dizziness, electrolyte imbalance, a certain amount of muscular degradation, and interaction with your medication
FAQs
1. Will all of the weight I have lost in three days come back when I eat?
A: A large part of your rapid weight loss will come from water and glycogen, which can quickly reappear when you start eating your normal carb diet in a day or two, because your glycogen stores will be replenished and will hold water. However, fat loss in fasting will be more permanent, but this will be small after three days.
2. How much of my weight loss will be from muscle?
A: Some breakdown of lean tissue will occur during early fasting, but this will be a percentage based on your composition, activity level, and available proteins. A short fast will see some muscle tissue breakdown, but primarily fat usage will kick in after your glycogen stores are depleted. To reduce losses of muscle tissue, you can refeed with protein and resistance training when you’re eating.
3. Can a 3-day water fast “reset” my metabolism?
A: There is no way to prove a guaranteed 72-hour fast will have a “metabolic reset,” since you will notice changes in your metabolism with ketosis or hormone responses, but a good diet and medical attention, if necessary, will benefit your metabolism.
4. Is it better than a 500-1000 kcal/day low-calorie diet?
A: A moderate calorie restriction with sufficient protein and nutrients is mostly safer and more feasible than harsh short fasting diets when it comes to burning fat. Methods of intermittent fasting, providing a calorie deficit each week, can prove very beneficial for people.
5. How do you break a three-day fast?
A: Slow start with a light meal: small portions of balanced food – digestible proteins(yogurt, eggs), steamed vegetables, and a small amount of complicated carbohydrates. No massive, oil-rich meals, which will provoke vomiting, distention, or re-feeding syndrome.
6. Why may a medically supervised 72-hour fast be indicated?
A: Yes, some tests will require a 72-hour fast ( insulin tests), and some will undertake a medically supervised extended fast using only water in a controlled medical setting. Prolonged water fasting under medical guidance must never be attempted when being done for medical reasons.
7. If I want to lose fat, how can I follow a proven scientific approach?
A: Try for a sustainable calorie deficit each week with portion control, higher protein intake, whole foods, incorporate resistance exercises to maintain muscle mass, focus on sleep, and think about time-restricted feeding or strategic intermittent fasting if it can be incorporated into your lifestyle. Methods such as these work better at burning fat with less risk to your health than water fasts.
