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How Much Weight Can You Lose Semi-Fasting for One Month?

author image Carly Schuna
Carly Schuna is a Wisconsin-based professional writer, editor and copy editor/proofreader. She has worked with hundreds of pieces of fiction, nonfiction, children's literature, feature stories and corporate content. Her expertise on food, cooking, nutrition and fitness information comes from years of in-depth study on those and other health topics.
How Much Weight Can You Lose Semi-Fasting for One Month?
Severely reducing calories can help you lose weight, but it's not healthy. Photo Credit Karisssa/iStock/Getty Images

Following a temporary fast may boost focus and help with healthy weight loss, but no research demonstrates long-term benefits for fasting periods that last up to one month or longer. It’s likely that such fasts will lead to weight loss, but they may have negative effects. It’s necessary to save or burn about 3,500 calories to lose 1 lb. of fat, so depending on how many calories you restrict during your month-long fast, you may be able to lose 10 lbs. or more.


Although “fasting” means different things to different people, it’s a term that generally refers to restricting part or all of your normal daily caloric intake to lose weight or rid the body of toxins. Eating significantly less food than you normally do is likely to accelerate weight loss and may even result in up to 1 lb. of weight lost per day of full fasting.


Several types of fasting and semi-fasting diets exist. In the most extreme version, you might choose to eat no food for several days at a time or alternate days of eating light meals and eating nothing at all. In another variation, you may restrict caloric intake each day down to about one-half of what you normally eat. Yet another semi-fasting diet could involve eating only whole, natural foods and cutting out all desserts, refined food items and processed foods. All are likely to result in weight loss; the most extreme variations may bring more weight loss, but they may also come with the biggest health risks.


By eating fewer calorie-rich foods and more fruits and vegetables, you may be able to eat even more food than you normally do but still consistently lose weight by decreasing net calorie intake. However, it’s important to keep in mind that the body needs a minimum number of calories to survive and thrive each day, and safely following diets of fewer than 1,000 or 1,200 calories may require medical supervision. The International Natural Hygiene Society notes that an average member of the public notices few differences between fasting and starving and should always fast under professional supervision.


Keeping up a prolonged fast can have significant physical effects on the body. Fasts can slow metabolism, which may interfere with long-term weight loss efforts and trick the body into storing fat. Fasting can also result in nutrient deficiencies or dehydration, especially if you don’t take care to eat a balance of items from all the main food groups and drink plenty of water throughout the process. Weight loss effects can vary. In one 2004 study from the Pennington Biomedical Research center in Baton Rouge, La., 16 subjects followed an alternate-day fasting diet for 22 days and lost an average of about 3 percent of body weight.


Before beginning a month-long fast or any type of detox diet, the Mayo Clinic recommends you get physician approval. Losing weight slowly, at a rate of 1 to 2 lbs. per week, is healthier in the long term than quickly dropping pounds through a fast or other risky method. The most reliable strategy for weight loss is balanced, low-calorie eating and exercise.

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