Discover what science says about intermittent fasting for weight loss and find out if this style of time-focused eating is worth all the hype!
Intermittent fasting is basically a general term used to describe various methods of manipulating meal timing to create large windows of time without eating. Theoretically, by following the suggested eating hours, you can lose weight, lower your risk of certain chronic diseases, and even give your brain a boost.
Over the past year, intermittent fasting has been increasing in popularity and interest largely due to social media influencers, celebrities, and TV shows promoting this new weight-loss trend. It’s easy to get distracted by the flashy titles and promised results rather than refer to the research. Before you jump on the intermittent fasting bandwagon, let’s take a look at the science that backs it up.
How Does Intermittent Fasting Work?
Many diets focus on what to eat, but intermittent fasting is more about when you eat. You only eat during a specific window of time and then fast for the remaining hours up to a day. For instance, you might try eating only during an 8-hour period each day and fast for the remaining 16 hours. Or you might choose to eat only one meal over 2 days in a week.
There are many different intermittent fasting schedules. The most common types of intermittent fasting can be classified into 3 types based on fasting hours; Alternate Day Fasting (ADF), The 5:2 diet, and Time-Restricted eating (TRE).
It’s important to check with your doctor before starting intermittent fasting, especially if you have a serious health condition. Once you get the go-ahead, then you can pick a fasting approach that works best for you.
For instance, you may choose to try the TRE method like the 16-8 fasting: eating for 8 hours and fasting for 16. Another, known as the 5:2 approach, involves eating regularly five days a week. For the other two days, you limit yourself to only one 500–600 calorie meal. An example would be if you chose to eat normally every day of the week except Mondays and Thursdays, which would be your one-meal days.
Longer periods without food, such as 24, 36, 48 and 72-hour fasting periods, are not necessarily better for you and may be dangerous. Going too long without eating might actually encourage your body to start storing more fat in response to starvation. Researchers also claim that it can take 2-4 weeks before the body becomes accustomed to intermittent fasting. You might feel hungry or cranky while you’re getting used to the new routine.
What Intermittent Fasting Does to the Body
Intermittent fasting burns fat, not sugar. When you fast, your body burns fat instead of sugar for energy, which can lead to fat loss and give your brain a boost. Like a machine, your body needs fuel to function; food is that fuel. During digestion, the stomach breaks down carbohydrates into sugar that your cells use for energy—to “fuel up,” so to speak. If your cells don’t use all the available glucose, it ultimately gets stored as fat.
During a fast, your cells switch from using glucose as their primary fuel source to burning fat. Thus, your fat stores, mainly triglycerides, get burned up for energy. This is why research has found that intermittent fasting leads to weight loss, as well as an improved cardiovascular disease risk profile.
Some experts say the shift can occur as early as 10 hours, and usually between a window of 10 to 16 hours of not eating. While others suggest the metabolism change is most pronounced after 18 hours of fasting. The breakdown of proteins for fuel won’t happen until about the third day of fasting. This suggests that intermittent fasting can help you lose weight while maintaining muscle mass.
What to Eat While Intermittent Fasting?
There are no specifications or restrictions about what type or how much food to eat while following intermittent fasting. However, during your eating window, “eating normally” does not mean going crazy. You’re not likely to lose weight or get healthier if you pack your feeding times with high-calorie junk food, super-sized fried items and sugary treats.
Anyone attempting to lose weight should focus on nutrient-dense foods like fruits, veggies, whole grains, nuts, beans, seeds, as well as dairy and lean proteins. Basically, the best foods to eat while intermittent fasting include things like avocado, potatoes, cruciferous veggies, fish, seafood, whole grains, nuts, and fermented foods. Focus on high fiber, unprocessed, whole foods that offer variety and flavor. It’s also key to remember water as a part of your daily routine.
During the times when you’re not eating, water and zero-calorie beverages such as black coffee and tea are permitted.
Intermittent Fasting Benefits
Some research shows that the intermittent fasting periods do more than burn fat. One study published in the New England Journal of Medicine revealed data about a range of health benefits associated with the practice. These include a longer life, a leaner body and a sharper mind.
Here are some intermittent fasting benefits research has revealed so far:
- Thinking and memory. Studies discovered that intermittent fasting boosts working memory in animals and verbal memory in adult humans.
n Heart health. Intermittent fasting improved blood pressure and resting heart rates as well as other heart-related measurements.
n Physical performance. Young men who fasted for 16 hours showed fat loss while maintaining muscle mass. Mice who were fed on alternate days showed better endurance in running. - Type 2 diabetes and obesity. In animal studies, intermittent fasting prevented obesity. And, in six brief studies, obese adult humans lost weight through intermittent fasting. People with type 2 diabetes may benefit: Most of the available research shows that intermittent fasting can help people lose body weight and lower their levels of fasting glucose, fasting insulin and leptin while reducing insulin resistance, decreasing levels of leptin and increasing levels of adiponectin. Certain studies found that some patients practicing intermittent fasting with supervision by their doctors were able to reverse their need for insulin therapy.
- Tissue health. In animals, intermittent fasting reduced tissue damage in surgery and improved results.
Is Intermittent Fasting Safe?
Most people try intermittent fasting for weight management, and some use the method to address chronic conditions such as irritable bowel syndrome, high cholesterol or arthritis. But intermittent fasting isn’t for everyone.
It’s best to check in with your primary healthcare practitioner first. Those that should steer clear of trying intermittent fasting, include:
- Children and teens under age 18
- Women who are pregnant or breastfeeding
- People with type 1 diabetes who take insulin. While an increasing number of clinical trials have shown that intermittent fasting is safe in people with type 2 diabetes, there have been no studies in people with type I diabetes
- Those with a history of eating disorders
To Fast or Not to Fast?
Overall, the science about intermittent fasting is mounting by the day. There is a growing body of scientific evidence that supports the promising benefits of intermittent fasting by activating the molecules and pathways that enhance health and boost our built-in mechanisms against diseases.
If done properly, intermittent fasting is a great strategy for weight loss, health improvement, and life span extension. But don’t be too fast to start fasting! Take it one step at a time and do what feels comfortable and right for your own body.
