Taking a break from eating (fasting) periodically throughout the week (intermittent) has become a popular weight loss technique among men and women. Many individuals choose intermittent fasting as a weight loss technique without fully understanding the risks.

There is a robust body of research studying the effects of intermittent fasting in humans. Intermittent fasting is thought to work by resetting the body’s metabolic system, a process which occurs in the liver when the body’s source of energy shifts from glucose utilization to free fatty acids and ketones.

Approaches

There are many approaches to intermittent fasting and not all approaches are the same. Examples of common intermittent fasting approaches include:

• Alternate-day fasting
• Modified fasting (5:2 diet)
• Time-restricted fasting

Alternate day fasting alternates days of fasting with days of eating. For example, an individual may choose to fast for 2 days out of the week on Mondays and Wednesdays and resume normal eating on Tuesdays, Thursdays, Fridays, Saturdays, and Sundays.

Modified fasting routines limits calories to 20% (25%) (500 to 600 calories) of energy consumption on fasting days. For example, an individual might eat normally on all days of the week, except for Saturday and Tuesday. On these days, this person would a small meal on Saturday and a small meal on Tuesday (approximately 250 to 300 calories per meal).

Fasting for 12 to 21 hours is an example of the time restricted fasting approach. For the time-restricted approach, many individuals choose to forego breakfast and extend the fast that naturally occurs while sleeping. For example, an individual may choose to eat their last meal at 6 p.m. and fast for 16 hours before eating their next meal at 9 a.m. the following morning. The ideal length of time for an individual to fast is not clear from existing research.

The risks and benefits of intermittent fasting vary with each individual, the specific technique used, as well as the length of time a person is fasting.

Benefits

Weight loss and decreased fat mass remain the most popular reasons for intermittently fasting. The effects of which can easily be measured.

Individuals may see an improvement in cardiovascular risk markers. Researchers have measured noticeable improvements in LDL cholesterol and triglyceride levels. It is also possible to have a reduction in blood pressure.

Risks

While many people have successfully incorporated intermittent fasting into their dietary routine, many choose to do so without fully understanding the risks involved. 

Due to the complicated process occurring in the liver, intermittent fasting has the potential to have unfavorable effects on glucose and insulin levels in the body. Abnormal liver function and protein deficiencies may also occur.

Nutritional deficiencies, electrolyte imbalances, alopecia (loss of hair), irregular menstrual periods, and decreased bone density also have the potential to occur.

Practical Advice

Intermittent fasting is meant to be a short-term approach and is not meant to be used for long, extended periods of time. When intermittent fasting is practiced for long periods of time or if an individual has a chronic illness, one may start to experience some of the risks described above.

Using intermittent fasting to compensate for overeating or poor nutritional intake has the potential to stress the body and disrupt your body’s normal metabolic system.

When incorporating intermittent fasting into a weight loss program, it’s important to remember to drink plenty of water (not energy drinks) and avoid large quantities of sugar and processed foods. The calories consumed should be nutrient dense.

Intermittent fasting is not a substitute for lack of exercise. Exercise remains one of the best ways to decrease weight, maintain muscle mass and tone, protect from cardiovascular disease, and control blood sugar levels.

Maintaining a healthy diet that consists of whole foods such as vitamin-rich vegetables and fruits, whole grains, lean protein, healthy fats, nuts, and legumes, is also recommended.

Disclaimer

Children, teens, elderly, and those with chronic medical problems should not attempt intermittent fasting. Intermittent fasting should not be done without primary care provider supervision. More research is needed in this area to better understand the body’s response (including risks and benefits) in both males and females. Please consult with your nurse practitioner or physician before proceeding with an intermittent fasting plan.