Fasting and Its Effects on the Body

Humans have been fasting for thousands of years.  It is not a new diet plan.  There was a time when one couldn’t just get out of bed, walk to the refrigerator and take out a dozen eggs and a package of bacon.  Humans had to hunt, gather or kill their food before they could eat.  Ancestors participated in fasting whenever food was unavailable and then feasted when the food was abundant.  In today’s modern world of an overabundance of food, fasting is not considered normal, and may seem strange to many.  What is research saying as it struggles to catch-up to our ancestors who knew of this secret?

Intermittent fasting requires followers to fast for anywhere from 12-20 hours daily which results in a cutting of calories.  Basically, it is an extended duration of minimal to no caloric intake. There are many different types of intermittent fasting and each requires a different time pattern and allows different liquids within the fasting period.  Fasting protocols vary from eating once a day, as on “The Warrior Diet” to fasting for 14-16 hours, as on “Time Restricted Fasting”. Technically, this is not a diet because there are no rules as to what you can and cannot eat, but it is more of a timing tool.  Common sense tells us that when we are not in the fasting period, it is not wise to choose outrageous amounts of empty calories or processed junk food.

Rodents have been studied for years to see what effects this eating pattern has on insulin sensitivity, inflammation, body composition, the aging process, metabolic health and cell biology. However, it is important to remember that a rat’s hormones do not identically match the hormones of a human being.  Rats have a shorter life span of only a few years so intermittent fasting for 12 hours would be similar to starving a person for a couple of days.  There are a limited number of human trials to date that study the health benefits of intermittent fasting.

The earliest research on caloric restriction, which began over 75 years ago, shows that it may add years to your life.  Cutting 25% of your daily calories has a long list of benefits, such as a reduction in blood pressure, inflammation, triglycerides, cancer risks, LDL levels and an increase in lipolysis, HDL levels and improved body composition.

By far, the biggest changes are seen in insulin signaling pathways which in turn increase the rate of lipolysis. Intermittent fasting reduces your blood glucose levels for hours at a time which increases your insulin receptors’ sensitivity when you do eat.  Insulin resistance is a wide-spread problem in today’s world thanks to an overabundance of refined fats, too much refined and simple sugars, and a diet low in minerals such as chromium and magnesium.

Insulin resistance occurs when the insulin receptors on the outside of the cell wall do not recognize a modest amount of insulin floating in the blood stream so the pancreas continues to pulse insulin into the blood until the amount registers with the receptors. Insulin resistance basically causes lipids to be stored in cells that aren’t meant to contain fat. These tissues are mainly the skeletal muscle tissue and the liver.  When you restrict all of your macronutrients during intermittent fasting, your body has no choice but to start metabolizing accumulated fat since there is nothing flowing through the blood stream to use as an energy source.  This fat may be intramuscular, adipose or even from a fatty liver.  As cells give up their on-boarded fat, the insulin receptors on the outside become more sensitive to the hormone insulin because they are now looking for an energy source as the amount of fat held in the tissue decreases. In simple terms, insulin is the hormone that determines how rapidly we metabolize fat.  When insulin levels are low, the body knows that carbohydrates are absent and fats need to be metabolized.  When insulin levels are high, carbohydrates can be easily metabolized and lipolysis is decreased.

Elevated blood sugar levels are dangerous to the walls of our arteries and also increase our blood pressure.  Whenever insulin is high due to elevated blood sugar levels, lipolysis is decreased.  Increasing the sensitivity of insulin receptors creates a situation where the insulin is better at disposing of glucose, either into the muscle cell or the fat cell (which is even better). The liver does not contain insulin receptors but this phenomenon of increased lipolysis allows the liver to be more efficient in its many processes, including using cholesterol to make vitamin D, bile and steroid hormones. This leads to many positive vascular changes.

When the liver uses cholesterol to make other necessary substances, it decreases the amount of LDL in the arteries through a process known as reverse transport. In reverse transport, the healthy HDL cholesterol, which we make when we exercise, flows through the blood stream scavenging for the unhealthy sticky LDL cholesterol.  Removing the sticky LDL from the arterial walls improves the elasticity of the blood vessels so hardening of the arteries becomes less of a risk.  Through reverse transport, HDL returns LDL to the liver where it is used to make bile for emulsifying fats, to produce the vitamin D from hormonal substances, and to produce steroidal hormones such as estrogen, testosterone and cortisol.

As reverse transport occurs, and LDL levels drop in the blood, this causes a drop in blood pressure and inflammation which decreases the risk for heart disease.  A decrease in inflammatory cells in the body also decreases the risk of cancers which thrive in an inflamed acidic body.

So think of intermittent fasting as taking a break from food,  which will do wonders for not only your health but also your waistline.  Research shows that subjects who fasted from 6 pm until 10 am the next morning cut 300 calories from their diets on average.  With 3500 calories making a pound, and doing this every day (300 x 7= 2100), participants can see a weight loss of over half a pound per week or two and a half pounds lost each month.  That’s over 25 pounds a year!


Melissa Layne, MEd, is a faculty member in the Exercise Physiology and Physical Education Departments of The University of North Georgia. She began her career over 30 years ago with a BS in P.E. and a Masters in Exercise Physiology. She has taught elementary PE, coordinated fitness programs for Royal Caribbean and Home Depot, and managed an exercise program for a team of orthopedic surgeons. Melissa is the author of WATER EXERCISE (Human Kinetics 2015), a member of the educational faculty and a DVD featured presenter for SCW and ACSM. She is known for her ability to take complicated subject material and break it down into easily understood examples and pieces.