Intermittent Fasting: The Science Behind Calorie Restriction
In this monthly column, VitaLife MD’s Carley Cassity helps us navigate the most exciting research in health and wellness while offering guidance on key holistic health practices to help improve our overall resilience. A Family Nurse Practitioner, Carley Cassity treats her patients by integrating both western and eastern modalities and channels that background into her writing here — backed with evidence and scientific resources.
Most patients (in Los Angeles) are experienced with intermittent fasting by the time they walk into our office. I find that the majority of my clients are utilizing intermittent fasting for weight loss but are unaware of the cardiovascular, cognitive, preventative and anti-aging benefits.
To understand how fasting benefits the body, we must first understand a little about food as energy. When we eat, our cells break down the food into molecules that are then used as energy or stored for later use – as fat. Glucose and fatty acids are the two main sources of fuel for our cells.
Glucose is easily used as immediate energy, while fatty acids are stored for later energy use. However, if we are constantly replenishing the body with new glucose and fat (as we often do in our culture) then we are never utilizing our fat storage. During fasting, the body must utilize its fat stores through the break-down of fatty acids to ketone bodies. This is a much more efficient production of energy for the body. In addition, ketone bodies signal other molecules and proteins. And these other molecules and proteins have known beneficial effects on health and aging.
To date, the numerous studies in rats, mice and humans all concur the same benefits of intermittent fasting: weight loss, decreased cholesterol, decreased inflammation, improved insulin sensitivity and improved heart health. https://www.nia.nih.gov/news/research-intermittent-fasting-shows-health-benefits
There are three very widely studied intermittent fast regimens:
Alternate Day Fasting – restricting calories to 500 or less every other day. The general guidelines for this type of fast are that the person follows a 500 calorie diet every other day with regular eating days in between. Studies have shown a reduction of 3-8% of body weight with this type of fast, but do not find that it is superior to everyday calorie restriction. However, some find this type of alternate day fasting to be more sustainable.
5:2 – following a restricted caloric intake 2 days per week. The 5:2 fast outlines regular eating 5 days/week with a 500 calorie fast 2 days out of the week. It is important to note for all fasts that following a healthy overall diet on the fasting and non-fasting days is very important. This schedule of 5:2 was not found to be any more beneficial than other fasts, however it does offer more flexibility since the calorie restriction is only 2 days a week.
Time Restricted Feeding - most commonly 18 hours of fasting with 6 hours of feeding. This type of fast is widely used and consists of a scheduled feeding time of 6 hours with 18 hours of fasting. Often a modified version for women of 16/8 – 16 hours of fast, and 8 hours of feeding. This consists of no caloric intake during the fasting period, with normal feeding in the 6-8 hour window. This type of fast shows 1.3%-4% reduction in body fat, reduced cholesterol and fasting glucose levels. Also to note was that human trials reported less variation in anger, confusion, fatigue, depression and tension with this type of fast.
For each of my patients, I chose the program that best fits with their lifestyle. I personally follow a time restricted feed 5-7days/week for the daily benefits of energy and improved cognitive function which I find with reduced calories on a daily basis. Also, patients often have to work their way up to each of these programs. For the 500 calorie days, it requires slow progression of weekly calorie reduction in order to arrive at the 500 calorie day. The same with Time restricted feed as it often takes a few weeks of slowly increasing the fasting time frame to arrive at the 16 or 18 hour fast. Some variations of calorie restriction or fasting duration may need to be modified for women, elderly or those with specific health conditions, but this all depends on the individual health status of the person.
Intermittent fasting reduces cellular stress. During periods of fasting the body is able to reduce inflammation, defend against oxidative stress, and engage in cellular repair and renewal.
This in turn reduces the incidence of other disease states and ensures longer life span.
I attempt to educate all of my patients about the numerous benefits of intermittent fasting and recommend adopting this as a lifestyle habit and not a short-term weight loss tool.
Carley Cassity is a Family Nurse Practitioner with extensive experience in holistic health. Practicing preventive, natural medicine, yoga and meditation in her personal life for many years, she realizes the importance of incorporating alternative and complementary practices into western medicine.
In her current role at VitaLife MD, Carley works alongside a well-established Los Angeles based French physician treating patients throughout the lifespan with an emphasis on preventative care and anti-aging. At VitaLife MD, Carley utilizes herbs supplements, hormone replacement, and peptide therapy to assist patients as they transition through the aging process. She also recognizes the importance of spiritual and emotional health and works in collaboration with acupuncturists, therapists and healers to incorporate meditation, breathwork, psychotherapy into the treatment plan.