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Intermittent Fasting Pros and Cons: What the Science Says

Intermittent Fasting Pros and Cons: Should You Try it

Growing science supports that you may reap many health benefits from the popular diet trend of intermittent fasting. But just like most diet fads, your success or failures with intermittent fasting depends on how you approach it.  

We reviewed the research and took a hard look at the pros and cons of intermittent fasting. Here are some tips to help you avoid the common pitfalls of fasting and glean some unexpected pros of the process. 

What is Intermittent Fasting?

Intermittent fasting is a dietary approach that focuses on time restricted eating - fluctuating between specific periods of fasting and ‘allowed eating’ time that is usually limited to 8 or fewer hours each day.

There are many potential patterns but some common example time frames for intermittent fasting include daily fasting for 16 hours with 8 hours of eating (16:8 method) or 24 hour fasting a couple times each week (5:2 method).  

The Pros: 4 Potential Benefits of Intermittent Fasting 

Health claims of an intermittent fasting diet range from helping with weight loss to preventing heart disease, type 2 diabetes and even cancer.

While much of this research comes from animal studies, some human data has also offered promising results - especially related to the potential for helping with weight loss and improving some aspects of nutrition related diseases such as diabetes (1,2).  

Here are four potential benefits of intermittent fasting that are supported by research:

1. Intermittent Fasting Supports Weight Loss

The main goal for most people interested in intermittent fasting is to lose weight.

Fasting each day for a period of time promotes calorie restriction and leads to weight loss.

In fact, eating fewer calories than you burn has the most scientific support to accomplish weight loss.

Weight loss (and maintaining a healthy weight) in of itself lowers the risk of most nutrition related chronic diseases including high blood pressure, heart disease, stroke, and diabetes.

So, does the weight loss from intermittent fasting happen just because people are eating fewer calories? Maybe. But if it helps you lose pounds then fasting can still be a great dieting tool. 

But there also may be more to the story.  Some studies suggest that short term fasting may actually increase your metabolism leading to more weight loss than what you would achieve by just cutting calories alone (3).

This is controversial however and more research needs to be done to confirm the effect of fasting on metabolism. 

2. Intermittent Fasting Could Help with Insulin Resistance

Lower blood sugar has been found in some people who intermittently fast - which also happens to be a central goal in the prevention and treatment of diabetes (4). 

Insulin resistance is thought to be a major cause of type 2 diabetes. High levels of insulin in our bloodstream exist when the body is frequently supplied with glucose.  The amount of insulin circulating in our blood lowers in between meals. So it makes sense that fasting for a period of time may decrease the amount of insulin release. 

Intermittent fasting gives the body a break from glucose surges. This may help minimize insulin resistance.

Both lower blood glucose and improved insulin function help to prevent and treat diabetes. 

These theories of a beneficial effect of fasting on glucose and insulin seem to hold in studies on rodents and some human trials. But because so few controlled studies have been performed on people, more research is needed to elucidate the effect of intermittent fasting on glucose, insulin and diabetes (1,2,5). 

3. Intermittent Fasting May Help Reduce Cholesterol 

Your cholesterol might also improve after intermittent fasting. Better lipid profiles have been found after intermittent fasting including a lower overall cholesterol, lower bad cholesterol (LDL - low density lipoprotein), and lower triglycerides in addition to a higher good cholesterol (HDL - high density lipoprotein) (6,7). 

There’s not enough evidence to definitively say that time restricted feeding or fasting in of itself helps our cholesterol and more studies need to be done to know its effects for sure. 

4. Intermittent Fasting Might Support Heart Health 

Research on rats and mice has shown promise that intermittent fasting helps to protect our heart. This seemed to hold true for both preventing heart disease and helping recovery after heart attacks in these rodents. 

Risk factors for heart disease like hypertension and heart rate variability have also improved in association with intermittent fasting (1,2). 

While this may seem exciting, people don’t always respond the same as animals to these interventions and more studies need to be done in people to understand the role of intermittent fasting on heart disease. 

The Cons: 4 Intermittent Fasting Side Effects to Watch For

So far, the effects of intermittent fasting seem overall positive. But there can always be a downside to every diet if it’s not approached in the right way. 

Here are four potential risk factors or "cons" associated with intermittent fasting: 

1. Intermittent Fasting Can Still Lead to Weight Gain

Feeling starved during your fasting period might make you more prone to binging behaviors when you’re not fasting. If you end up going completely rogue on your non-fasting periods you’ll still gain weight.

Eating more calories than what your body burns will lead to a long term increase in body fat even if you consistently fast for 16 hours each day. 

Fasting Tip

The quality of your food is crucial. Meal plan ahead to ensure you make nutrient dense food choices during your non-fasting periods. Stay within your calorie limit each day. 

Intermittent fasting doesn’t replace healthy eating or calorie control. 

In fact, it doesn’t tell you anything about what you should eat, which is obviously a critical part of successful dieting. Think of it as a tool that helps us optimize when we should eat. 

2. Fasting Can Make You Feel Tired and Moody

Fatigue and/or mood changes including irritability are common complaints from people who skip meals.

Many people also experience decreased cognitive functioning that they feel affects their ability to work. This seems to especially be true in people who fast for extended periods of time such as those on an alternate day fasting eating plan (8).

Fasting Tip

Short term fasting can be a more sustainable approach for many people. Not eating for 12 hours or even 16 hours by skipping breakfast can be a more successful long term plan for many people.

If you do extended fasting, try choosing a day of the week or period of time that you don’t need to be very active or deeply concentrate.   

3. Skipping Meals Can Cause Headaches, Dizziness, and Nausea

Long periods of fasting can lower your blood sugar levels and leave you feeling lightheaded, dizzy, with headaches, and/or nausea.

Long periods of fasting can lead to lower blood glucose levels. Blood glucose levels that are too low leads to a condition called hypoglycemia.

While small decreases in your blood glucose can have a positive effect on your health overall, it can be dangerous or even deadly for people with type 1 diabetes and in people who are on some diabetic medications (9). 

Fasting Tip

If you have medical problems, talk to your doctor to make sure it's safe to try intermittent fasting. 

4. Restrictive Eating Can Lead to Disordered Eating 

Any diet that supports skipping meals or restrictive eating can trigger some not so great food relationships in some people. Especially when the positive weight loss effects are directly impacted by not eating at all.

The more you fast, the more calories you can restrict, and the more weight you can potentially lose. 

This can lead some people take intermittent fasting too far. And not eating enough calories each day can lead to nutrient deficiencies and some develop eating disorders. 

Fasting Tip

Make sure you’re continuing to get all of the nutrients you need to fuel your body through fasting!

Work with a dietitian or doctor to make a meal plan that works well for you. 

You can also try intuitive eating that removes the focus away from calories and willpower and focuses your efforts on getting in tune with what you body needs to thrive - regardless of what time of day it is or when your next approved eating window is. 

Should You An Try Intermittent Fasting Diet? 

There are many potential benefits of intermittent fasting but the research is still too limited to say for sure if this is something you should be incorporating in your life to help your health (10). 

If you choose to try intermittent fasting, continue to incorporate basic nutrition principles that have been well established by science to optimize your health including calorie control to maintain a healthy weight and a balanced diet that incorporates all of the essential micronutrients. 

Always involve your doctor or dietitian in any major changes to your nutrition to make sure that your new approach is safe for you.  

Whether you are trying intermittent fasting or just looking to lose weight, your nutrition is more than half the battle! Get your healthy diet on lock with portion perfect, ready to eat meals delivered straight to your home. 

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