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Intermittent fasting is a pattern of eating as usual then not eating for a set time period and may have some heart health benefits. Julia Zumpano, registered dietician with the Department of Preventative Cardiology at the Cleveland Clinic, answers "what is intermittent fasting?" and explains why it works for some people.

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What is Intermittent Fasting?

Podcast Transcript


Welcome to Love Your Heart, brought to you by Cleveland Clinic's Sydell and Arnold Miller Family Heart, Vascular and Thoracic Institute. These podcasts will help you learn more about your heart, thoracic and vascular systems, ways to stay healthy, and information about diseases and treatment options. Enjoy.

Julia Zumpano, RD LD:

Hello, my name is Julia Zumpano. I'm a registered dietician with the Department of Preventive Cardiology at the Cleveland Clinic. I've primarily focused on cardiac patients, but also see patients who have risk factors for cardiovascular disease, such as diabetes, high blood pressure, metabolic syndrome, obesity, renal issues and even some weight and family history of cardiovascular disease.

So today, I'm going to discuss intermittent fasting. Fasting is when you're not eating or drinking for certain periods of time. Intermittent fasting is a pattern of eating, where you set aside periods of time where you fast and periods of time where you have an eating window. So typically, intermittent fastings include alternate day fasting, where you can eat one day as a typical day and eat very little the next day. Or time-restricted eating, which is one of the most common forms of fasting, is where you restrict your eating window to an eight to 10 hour window and fast for 14 to 16 hours, even possibly up to 18 hours a day, typically occurring after your last meal or your dinner meal throughout the evening and while you're asleep and restricting until the morning.

This eating pattern works because it syncs with your internal clock, which is called your circadian rhythm. Our digestive system is programmed from birth to eat during the day and to rest at night when we sleep. Eating at night requires our bodies to continue producing insulin during the hours when we do not require much sugar for energy. So as a result, more sugar gets stored as fat. This is why eating at night increases your risk of diabetes and obesity. What happens to our bodies when we're fasting? So generally, our body uses glucose as our main source of energy, but when we fast, we no longer use glucose. But we tap into our own body's fat stores for energy. That creates a state of ketosis, which is a similar state that we can obtain in a ketogenic diet or a very low carbohydrate diet, but the state of ketosis has been shown to decrease insulin levels.

It has also been helpful for decreasing inflammation and has multiple health benefits, when done properly. Generally, fasting means that you should not be eating any solid food or any drinks with calories. Coffee is an exception. And so is tea. They technically have five calories or less per serving, but do not contain any carbohydrates and sugar, therefore, cannot take you out of fast. Of course, you can drink water, black coffee or unsweetened tea, and in some cases, you can even have a small amount of cream in your coffee, as long as it doesn't provide a substantial number of calories or carbohydrates. When you're not fasting, what you eat still matters. As is true with any diet, the best results are obtained with healthy food choices. So, making sure you're focusing on a lot of lean protein, fiber in the form of vegetables, fruits, and whole grains, and then, healthy plant-based fats, minimizing or avoiding any junk foods and snack foods, sweets or desserts, focusing on whole foods and minimizing beverages that contain calories or even artificial sweeteners. So, water is ideal.

So why would someone choose to intermittent fast? Well, there have been some preliminary studies that show fasting can drop levels of insulin, it can decrease aging and the progression of disease over time, it can also help symptoms of metabolic syndrome. Metabolic syndrome is a multitude of factors, including high blood pressure, elevated blood triglycerides, elevated blood sugar, increased waist circumference, obesity and high levels of bad cholesterol. There can also be a decrease in inflammation from intermittent fasting. The inflammatory response is responsible for a lot of disease states, so decreasing inflammation also helps decrease your levels of free radical production. Free radicals damage cells, so we want to decrease the amount of cell damage. Intermittent fasting may also improve the body's response to a hormone called insulin. Insulin helps control blood sugar levels. Better cholesterol and blood sugar levels can lower your risk of weight gain and diabetes, which are two risk factors for heart disease.

So, what does the research say? Research on intermittent fasting is mixed. Some studies say they can decrease your bad levels of cholesterol or your LDL. It can also improve your body's response to insulin, as we mentioned before, but other studies have suggested that skipping breakfast, a form of intermittent fasting, can increase your risk of heart disease. In a review of the studies on intermittent fasting found that weight and blood sugar changes reported were small. Much more research is needed to determine whether fasting can reduce your risk of heart disease.

So, who should not fast? Definitely avoid fasting if you're underweight, if you have an eating disorder or history of an eating disorder, you're pregnant or breastfeeding, you take medications for diabetes or have poorly controlled diabetes, you have a history of low blood sugars, which is also called hypoglycemia, you have end stage liver disease or you have chronic kidney disease.

Any type of diet should be discussed with your doctor to make sure it's safe before you begin. So, there are some negative side effects to fasting. Oftentimes, you could feel hungry, fatigue, insomnia, irritability, headaches or nausea. Most often, these side effects will go away over time, but in some cases, they don't. So, you have to be very aware of how your body feels and how long it takes to adjust and whether or not this plan is right for you. Remember that there is more than one way of fasting and creating that fasting state and the benefits can really be adjusted based on what's best for you. Ideally, meeting with a dietician can really help you determine the best way to fast and best timings and help you really get the benefits with minimizing the negative side effects as much as possible.

So, is this style of eating sustainable? We know the benefits do extend long term, and this type of fasting and lifestyle will go a long way. I would highly recommend it if it's something that is feasible and manageable for your body and your lifestyle. It really can be a long-term way of eating, especially if you determine a plan that fits within your lifestyle and what will work for you. The most common form of fasting I recommend is a 14 to 16 hour fast, which is done overnight. The reason I recommend this is because a lot of times, we do unnecessary eating after dinner. And a lot of our snack choices are unhealthy, tend to have high amounts of calories, especially in the form of fat or carbohydrates, and these snacks tend to be habitual and leading to excess amount of overall intake of sugar, carbohydrates and fats. So, if we can really focus on eating really healthy meals throughout the day, you shouldn't be hungry after dinner, and this is a great time to avoid snacking and eating. And it's a great time to really gain that benefit of dropping your level of insulin and decreasing unnecessary calories, which again, will help with weight loss, decreasing your glucose, triglycerides and blood pressure.

So really also keep in mind some of the food choices you're making in regard to salt and sweets. So salty and sweet foods are what we tend to snack on the most, and those can have negative effects on blood pressure, as well as blood sugar. So, what we can begin is just starting with avoiding anything to eat or drink after dinner, other than water, tea, or black coffee, and then, starting just there, and then eating your breakfast at your normal time. And then, as your body adjusts, you can slowly start to change your breakfast time a little bit later in the day, to create and extend, making that fast up to 14 to 16 hours.

When we fast up to 14 hours, we know we've created some form of ketones at that point. So, 14 hours is really the key to give us some benefits. 16 hours gives us a little boost, but at least if we can go 14, we'll get a benefit, even 12 hours. So, if you're cutting off your eating at seven, that means we don't want to eat breakfast before 7:00 AM for a 12 hour fast. We would do 9:00 AM for a 14 hour fast, and then, 11:00 AM for a 16 hour fast. Again, this doesn't have to be done every day. I typically suggest my patients begin this three days a week, and then, they start to begin to add a couple more days if the fasting method works for them.

So quick takeaways. Intermittent fasting may be safe for some people, but not for everyone. Skipping meals may not be the best way to manage your weight. Choose a method that still will work for your lifestyle. You always want to set yourself up for success. Try to take this opportunity to improve your diet. What you eat still really truly matters. The best results are really obtained from healthy food choices, so try to take out some unhealthy snacks and try to create regular eating times and schedules. Stay active, follow healthy eating, and avoid mindless snacking. Restricting the hours, you eat can improve your health and can help you lose weight too. And lastly, be kind to yourself. If, for some reason, you mess up, just start again the next day. It's trial and error. Nobody's perfect. We're all trying to figure out how to keep our bodies as healthy as possible, so be kind to yourself. And enjoy.


Thank you for listening. We hope you enjoyed the podcast. We welcome your comments and feedback. Please contact us at heart@ccf.org. Like what you heard? Subscribe wherever you get your podcasts or listen at clevelandclinic.org/loveyourheartpodcast.

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