By Courtney McMahan, RD

Perhaps you’ve heard your coworker talk about how they only eat one meal per day at five pm. Maybe your friend told you about how much weight they’ve lost from not eating past seven. Or maybe your aunt is convinced that fasting for an entire day once per week is going to help her lose belly fat. And you might have heard all these eating schedules loosely categorized as “intermittent fasting.” But is intermittent fasting healthy? And if so, what approach is best?

What is Intermittent Fasting?
There’s no shortage of diet programs telling you what to eat, but intermittent fasting is unique in that it puts the focus on when you eat.  

According to a neuroscientist from Johns Hopkins who has studied intermittent fasting for twenty-five years, our bodies are equipped to go without food for many hours or even multiple days. 

In our modern age, it's easy to forget that we haven’t always had endless amounts of processed, packaged snacks or a 24/7 fast food drive-thru on every corner. Our prehistoric ancestors had to hunt and gather to survive and thus would have to go long stents between meals. 

Even a few decades ago, before the invention of the internet and unlimited streaming, people on average went longer stents without eating because they went to bed earlier. Now, with nonstop entertainment available at our fingertips, it is much more common to be up at all hours, which often leads to eating late at night. 

The logic behind intermittent fasting is that by going for longer periods without food, you can receive positive metabolic changes. It works by prolonging the time when your body has burned through all the calories you’ve eaten, which causes your body to switch over to burning stored fat. 

Potential Benefits

Weight loss

Some research has shown intermittent fasting can help with weight loss. However, it’s important to note that research comparing intermittent fasting to calorie restriction has found no difference in weight loss. So intermittent fasting will only help with weight loss if it makes it easier for you to restrict calories. 

Improved blood glucose and lipid metabolism

Some studies have shown that intermittent fasting may reduce blood glucose, insulin, A1C, total cholesterol, LDL cholesterol, and triglycerides. 

Reduced inflammation

Intermittent fasting may reduce certain inflammation markers like C-reactive protein. 

Which schedule is best?

If you decide to give intermittent fasting a try, my recommendation is to do the method known as time-restricted feeding. With this method, you restrict your eating to certain hours of the day instead of going full days without food. By choosing this method, you reduce the risk of negative side effects like hunger, cravings, headaches, dizziness, sleep disturbances, and malnutrition. 

In this method, you might keep your eating within an 8 or 10 hour window and then fast for 14 to 16 hours. This way, you are still able to get multiple balanced meals and snacks each day and to meet all of your nutritional requirements. For example, you might decide to eat all your meals between 9am and 6pm and fast from 6 to 9 the next morning.

What are the risks? 

• Intermittent fasting could cause negative side effects like lethargy, irritability, headaches, and constipation. 

• It could cause overeating. Some methods of intermittent fasting are very similar to the restrict-binge cycle that is a common form of disordered eating. 

• Intermittent fasting is not good for those who have a history of an eating disorder, as the restriction may trigger disordered habits. 

• Intermittent fasting is not good for those who are at risk of being underweight, especially elderly people who are at risk, as it could cause too much weight loss or malnutrition. 

• Intermittent fasting could be dangerous for those with certain conditions and taking certain medications. For those taking blood pressure medications, it could cause electrolyte imbalances. Skipping meals and severely limiting calories can also be dangerous for those with diabetes. 

Conclusion

If you are a person with diabetes, on blood pressure medication, with a history of eating disorder, or at risk of being underweight; it is probably best to stick to your normal eating schedule. 

If you are a generally healthy and well-nourished person who wants to lose a few pounds and is having trouble sticking to a calorie deficit, intermittent fasting could make it easier for you to stay within your target each day. Go with the time-restricted feeding method to reduce the risk of malnutrition and negative side effects.

Even if you don’t go with a strict eating window each day, if you find yourself eating from 6am to midnight every day, it could be beneficial to try to make your eating window a bit smaller to give your body a longer overnight fasting period. 

It’s important to note that many of the benefits of intermittent fasting are the same benefits that are seen in calorie restriction, and there are many ways to restrict calories. So if intermittent fasting doesn’t work for you, there are other equally-effective ways to lose weight. As always, if you have any doubts, it's best to check with your doctor or dietitian before starting any new diet.