Fasting is a practice that has endured centuries. It is one of the most ancient traditions in human history. Greek physician Hippocrates recommended abstaining from food or drink for his patients as early as 400 BCE. Practiced by many cultures and religions, our modern day is beginning to see fasting appear in research more and more often. Fasting is defined as abstinence from consuming food and/or beverages for a period of time.

Recently, fasting has been studied as a lifestyle management strategy to benefit chronic, non-infectious diseases. Currently, 66% of the American population is diagnosed as prediabetic or diabetic and overweight or obese. These numbers are startling. We have seen its effect on those that have contracted COVID-19 resulting in longer recovery time or even more fatalities. Because diabetes is a blood sugar dysregulation condition that results in vascular disease, other comorbidities usually follow such as kidney and cardiovascular disease.

The reduction of chronic disease is where fasting can prove beneficial. Some benefits fasting research has shown is weight loss, improved concentration, prevention of insulin resistance, better cholesterol metabolism and increased longevity according to Valter Longo, PhD at USC Longevity Institute and the Edna M. Jones Professor of Gerontology at the USC Leonard Davis School.

Fasting can be categorized as:

1.) Intermittent Calorie Restriction (ICR) – also known as whole-day fasting, is the simplest form of intermittent fasting and involves fasting for more than 24 hours, two or three times a week with normal food consumption on the other days of the week.

2.) Alternate Day Fasting (ADF) – involves alternating non-fasting days where participants consume food with normal eating patterns followed by fasting days where only 25% of the usual dietary intake is consumed (~500 kcal).

3.) Time Restricted Feeding (TRF) – eat or feed strictly within in a specific time period. For example, 8 hours feeding, and 16 hours fasting- which generally includes your 7-8 hours of sleep. This is a 16:8 fast. Other forms may be 12:12 or 14:10.

4.) Fasting Mimicking Diet (FMD) – this is a calorie restricted eating plan, about 50-60% of normal calories for 4-5 days. This 5-day plant-based, low amino-acid substitution diet, consists of soups, broths, liquids and teas. Calorie content declines from Day 1 , about 1200 calories, to Days 2–4, about 600 calories. This is usually a pre-package purchased food kit, sold under the name ProLon.

The main differences between these protocols are the severity of caloric restriction, the abstinence from food/beverages per day and the frequency of caloric restriction per week.

As with most of my nutrition advice, it does depend on your state of health. Fasting in any form as listed above is not for you if you show signs of malnutrition, have disordered eating, are insulin dependent Type 1 diabetic, or are pregnant. Fasting is also not indicated if you have a high-stress state, meaning high cortisol or a dysregulated hypothalamic-pituitary axis.

It is also of key importance that in the “feeding” period you are getting enough nutrition to maintain good health. Oftentimes, I have patients that come to me and we see that they have micronutrient deficiencies because they are not getting enough nutrient-dense foods with their intake. I also see that some people develop GI problems due to low fiber in the diet. The gut microflora can change in just a few days without the right prebiotics of which fiber serves. Others that think they are fasting and may not be technically eating but are still having their “bulletproof coffee” may unknowingly be breaking the fast and not reaping the benefits.

If you are interested in the health benefits of fasting, in concert with your healthcare provider, perhaps start with a 12 hour fast from the last meal to the next morning meal to see how you feel. Monitor this for a week and then try extending your time by one hour, but only if you maintain good nutrition in your feeding periods, have restful sleep and stay fully hydrated.