What You Need to Know About Fasting for Weight Loss

People have fasted for centuries, often as a religious practice.

History of Fasting

Fasting for medical purposes is thought to have started with Greek physician Hippocrates, who recommended abstaining from certain food and drink for specific illnesses or symptoms. A better understanding of the effects of fasting was achieved during the 19th century based on studies involving animals and humans.  The ways in which people fasted became more varied during the 20th century, which brought about an even better understanding of the human body and its nutritional requirements.

Fasting today has become increasingly popular as a practice for weight loss. A form of fasting that has been gaining attention in known as “intermittent fasting,” and is based on a rotation of eating and fasting periods.

Fasting Methods

While people fast for different reasons and in different ways, fasting for weight loss has been classified into three groups.

  1. Time-Restricted Fasting Method
    • The time-restricted fasting method is popular because it falls in line with typical sleeping patterns. The 16/8 method consists of an 8-hour eating window and 16-hour fasting window. Similarly, the 14/10 method has a 10-hour eating window and a 14-hour fasting window. Someone practicing the 16/8 method, for instance, would only eat in the eight-hour period between 11 am and 7 pm.  The 14/10 method would permit eating between 10 am and 8 pm.
  1. Modified/Whole Day Fasting Method
    • This method consists of eating very few calories on fasting days and practicing standard eating patterns on non-fasting days. An example of the modified/whole day fasting method is the 5:2 approach,  which caps calorie intake at 500 for two days a week, while maintaining a normal,  balanced diet on the other five days.
  1. Alternate Day Fasting Method
    • The alternate day fasting method involves modified fasting every other day. Fasting days call for consuming only about 25 percent of normal calorie intake, while on non-fasting days regular eating patterns are practiced.


Pros of Fasting for Weight Loss

While benefits of fasting have been demonstrated in studies involving animals,  there are unanswered questions about the potential effects of fasting for weight loss in humans. A large, human-based study found that many people who fasted lost weight, and in some cases showed improvements in other health markers such as cholesterol and blood pressure. It is important to note, however, that studies are based on different methods of fasting and the characteristics of participants vary greatly, making it difficult to draw conclusions. There are many factors to consider in this approach for weight loss, and potential negative impacts should be considered.

Cons of Fasting for Weight Loss

Though research shows intermittent fasting can result in weight loss, there are disadvantages to consider as well. Fasting regimens can be challenging to maintain in the long run. And while weight loss may occur, there is also the possibility of muscle loss. Additionally, prolonged fasting can cause unhealthy eating behaviors and fixations on food.

More research is needed regarding the long-term health effects of intermittent fasting for weight loss and the potential for nutrient deficiencies and other negative effects.

Intermittent fasting is not recommended for pregnant or breastfeeding women, people with diabetes, or those who need to take medication with food. Children and adolescents should not be permitted to fast, and anyone with a history of eating disorders or disorder eating also should avoid fasting.

Individual Approach

Due to variations in intermittent fasting approaches and potential health implications, patients should always consult a primary care provider or registered dietitian before starting an intermittent fasting diet. A provider can help choose the right fasting method by considering medical history, medicine regimens, nutritional needs and long-term health goals.  Dietitians at ConnectCare3 are available to help you identify and personalize your nutrition goals.

Britannica. “Fasting”

Eat Right. “What is Intermittent Fasting?”

Cleveland Clinic. “Intermittent Fasting: 4 Different Types Explained”

Harvard T.H. Chan. “Diet Review: Intermittent Fasting for Weight Loss.”

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