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Intermittent fasting: What is it and how does it work?

INDIANAPOLIS (WISH) – Intermittent fasting is one of the fasting growing trends in the health and fitness community. But let’s be clear, intermittent fasting is not a diet. It’s a structured pattern of eating designed to help the body use fats as a primary source of fuel. And evidence suggests the method can increase a person’s longevity by regulating sugar levels and reducing inflammation. Weight loss is also one of the benefits. 

News 8 spoke with Rebecca Rivera, PhD, nutrition research scientist at the Regenstrief Institute to answer some questions about the trend. Below is the complete interview transcript: 

Gillis: Tell us about what intermittent fasting is. How does it work and what can it do for a person?

Rivera: Intermittent fasting has gained popularity especially in the past few years, but it’s actually been around for quite some time. The first research study on it dates back to 1997. And the interest in it came from noticing that researched animals were living longer during this intermittent fasting…just the scheduling in their feeding and their eating patterns. 

So, when we translate that to humans…that intermittent fasting…we can call that ‘restricted eating’ during a specific window of time. 

Gillis: You had mentioned three types of intermittent fasting or patterns of eating and each of them are designed to help our bodies burn what are called ketones. Can you explain the three types and explain what ketones are?

Rivera: Intermittent fasting is designed to help your body shift from using glucose–or sugar–as its primary fuel source over to using fats which include these ketone bodies. So, intermittent fasting kind of turns on or ‘signals’ different systems in your body in order to make that switch. When ketones are the body’s main fuel source that helps us burn fat faster which is the goal of weight loss and one of the targets of intermittent fasting. 

Gillis: We had talked about going first maybe 12 hours of fasting, then 16 and then 24 hours of fasting. Explain that progression.

Rivera: There are three common patterns of intermittent fasting and as you mentioned we can start a fasting window period for any number of hours. That is called “daily time-restricted fasting.” Most people would ease into that because fasting for 12 hours at a time is really difficult right away. So, you might start fasting for 6 hours then progress to 8, 10 and then 12 hours. 

You could then move to what we call a “5:2” pattern of fasting. That is eating regularly for 5 days out of the week and then fasting for two days. So, you would refrain from eating for an entire 24 hours on those two fasting days.

The third is called “alternate day fasting” and it’s just what it sounds like. You eat one day and then you fast the next. But sometimes fasting does include a small meal. Maybe around 500 calories on those days. 

Gillis: If someone wants to introduce this into their eating habits what should they do? Who might this be good for and who should avoid it?

Rivera: If you’re curious if intermittent fasting can help you reach your health goals definitely talk with your health care provider. Your physician, a dietitian, a nurse practitioner–whoever takes care of your personal health care. The reason we need to talk with them first before trying it is because they need to make sure you have an achievable plan in place. Intermittent fasting can be difficult to stick to and they can help you develop a plan that works best for you. It can also have some pretty important health implications. 

If not done properly it can be harmful to your health and actually prevent you from reaching your goal. For example, it could lead to really low blood glucose levels and if you have advanced diabetes you are susceptible to that. Also, during your eating days if you overeat your blood glucose could go really high and that is also dangerous and can occur in people with advanced diabetes. 

So, your health care provider needs to work with you to make sure those days and times you are eating…that you’re eating an appropriate amount of calories and also the right mix of foods. Your proteins, carbohydrates and fats are all very important so you’re getting all the nutrients you need to consume to reap the health benefits of intermittent fasting. 

News 8’s medical reporter, Dr. Mary Elizabeth Gillis, D.Ed., is a classically trained medical physiologist and biobehavioral research scientist. She has been a health, medical and science reporter for over 5 years. Her work has appeared in national media outlets. You can follow her on instagram @reportergillis and Facebook @DrMaryGillis