Fasting Diets

  • Author: Jennifer Warner
  • Medical Editor: Charles Patrick Davis, MD, PhD
    Charles Patrick Davis, MD, PhD

    Charles Patrick Davis, MD, PhD

    Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

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Quick GuideDiet and Weight Loss Pictures Slideshow: Healthy Dieting Myths and Facts

Diet and Weight Loss Pictures Slideshow: Healthy Dieting Myths and Facts

Fasting diets introduction

Fasting to lose weight is nothing new, but a new crop of trendy diets has brought the practice back into the spotlight.

Diets like the 5:2 Diet, Lemonade Diet, and others claim to help people lose weight fast and detoxify the body, but the research to support those claims is spotty at best.

What are intermittent fasting diets?

The 5:2 diet was recently the topic of a popular BBC documentary and book, and it's based on the principle of intermittent fasting (IF) or alternate-day fasting (ADF). Intermittent fasting means you eat normally at certain times and then fast or dramatically reduce your calorie intake at other times.

The 5:2 diet calls for eating normally on five days of the week and fasting (eating no more than 500 calories for women and 600 for men) on the remaining two days. Proponents of the 5:2 diet and similar fasting diets claim that they can increase lifespan, improve how the brain works, and protect against disease; but most of those claims are based on research conducted in animals like rats and mice.

There are some small studies in humans that suggest that intermittent fasting diet may help promote weight loss and reduce risk factors for heart disease, diabetes, and other weight-related health problems. For example, a small 2012 study in Nutrition and Metabolism showed 30 obese women who followed a liquid intermittent fastingF diet lost 8.8 pounds and 2.3 inches from their waistlines after eight weeks. (Excess body fat around the waist has been associated with a higher risk of heart disease.)

Another 2012 study in Nature suggests that the life-extending benefits rodents gained on fasting diets may not translate to larger and more human-like animals, like monkeys.

Medically Reviewed by a Doctor on 4/7/2015

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