The Truth About Intermittent Fasting
What is intermittent fasting? Does it work? We have answers
By Lauren Bedosky
Many eating patterns and diets spotlight what foods to eat or avoid for optimal health. Intermittent fasting, on the other hand, focuses on when to eat. Many experts believe this approach carries a range of health benefits.
What Is Intermittent Fasting?
Intermittent fasting is an eating pattern that cycles between fasting and eating on a regular schedule. Popular approaches include:
- Alternate day fasting, which involves fasting every other day
- Periodic fasting, which involves fasting for 1 or 2 days a week (also known as 5:2 or 6:1 fasting)
- Time-restricted feeding, or eating only during a specific time window each day, such as from 12:00 pm – 8:00 pm
While fasting, people turn to water and zero-calorie beverages such as black coffee and tea to stay hydrated.
What Are the Benefits of Intermittent Fasting?
Depending on how much you eat before or after your fasts, you may wind up lowering your overall calorie intake. Like other eating patterns that cut calories, intermittent fasting may help you lose weight. A February 2020 review in Canada Family Physician looked at 27 trials addressing weight loss and found that intermittent fasting led overweight and obese people to lose 0.8-13% of their baseline weight (the duration of the trials that were reviewed varied from 2-52 weeks).
But the benefits of intermittent fasting appear to extend beyond weight loss: There’s evidence that it may reverse insulin resistance and improve health in people with prediabetes and type 2 diabetes. However, there isn’t a ton of high-quality research on the topic, warns Jack Baron, R.D.N., a registered dietitian nutritionist and certified nutrition support clinician with the Einstein Healthcare Network in Philadelphia, Pennsylvania.
Researchers and health care professionals have started to suggest that intermittent fasting may help promote cognitive performance, improve blood pressure, and lower inflammation.
The practice of cycling periods of eating and fasting may work via a phenomenon some refer to as “metabolic switching.” After hours without food, glycogen stores in the liver are depleted, and the body begins to mobilize fatty acids for energy. This metabolic switch is thought to initiate changes in the body and brain that may lead to the health benefits.
What Are the Risks of Intermittent Fasting?
Skipping meals can be hazardous if you’re not careful.
People who are taking blood-sugar-lowering medications, for example, risk their blood sugar levels dropping too far without regular meals. These folks should talk to their physician before practicing intermittent fasting. Your doctor may want to adjust your dosage to prevent medical emergencies from very low blood sugar, says Su-Nui Escobar, R.D.N, D.C.N., a doctor in clinical nutrition in private practice in Miami, Florida.
Intermittent fasting may also cause side effects, such as anxiety, headaches, nausea, lethargy, constipation, and binge-eating once your fast is over. If you notice any of these side effects, choose another fasting schedule or ease into it more slowly to give your body time to adjust.
Some groups should steer clear of intermittent fasting altogether, including:
- Children and teens under the age of 18
- Women who are pregnant or breastfeeding
- People with a history of eating disorders
The Bottom Line
Cycling regular periods of eating and fasting may help you lose weight, improve insulin resistance, boost brain health, and lower blood pressure and inflammation. However, intermittent fasting isn’t for everyone. It’s a good idea to chat with your doctor before giving it a try.