Intro to Intermittent Fasting: What the Science Says
When you think “diet,” you probably think about a change in what you eat, not when you eat. But intermittent fasting, an approach to food intake that limits how much and when you consume calories, has gained traction in the health and wellness sphere in the last couple of years as a way to lose weight, prevent disease and potentially even increase longevity.
But does it really work? We took a look at what the science has to say about the benefits of this approach to provide you with a useful intro to intermittent fasting.
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First: What is Intermittent Fasting?
Intermittent fasting can be structured in a number of ways. Three of the most common are the 5:2 diet, alternate day fasting and time-restricted feeding.
The 5:2 diet allows for “regular” eating – 3 meals and snacks, as needed, at your daily recommended caloric intake – five consecutive days of the week, while limiting caloric intake to 25% of that recommended amount during the other two days. (For men, this might mean 2500 calories 5 days a week and around 625 calories on the fasting days; for women, it might mean 2000 calories and 500 calories.)
Alternate-day fasting is just as it sounds: switching between one day of normal eating and one day of fasting (again, around that 25% of your daily fuel needs).
Time-restricted feeding keeps energy intake consistent across each day but limits the number of hours during which you consume food: the fast occurs in the time between meals, which can be anywhere from 4 to 12 hours. You’d eat your daily caloric needs in a shorter period of time with a longer period of rest, digestion and absorption between meals.
Here's What Recent Researched Showed
Fasting may help with weight loss
Studies have shown that rats who live on slightly fewer calories than their “recommended” daily intake live longer and tend to be more resistant to disease compared to their counterparts who consume equal to or above the daily calorie recommendations.
Other studies have shown that rodents who eat more than they need one day (ie. feasting) and fast the next day consume fewer calories than they would normally. This approach to balancing fuel across several days was shown to be as effective at prolonging life as eating a calorie-restricted diet every day, suggesting that perhaps a balancing mechanism is at play: the body stores and utilizes the fuel from a “feast day” during a day when no new fuel is available. If fewer calories are taken in and stored fuel is used, weight loss may occur.
Alternate-day fasting in particular has been shown to be a safe and sustainable weight loss tool. It has been shown to reduce weight and body fat composition over an eight-week period, and does not appear to increase risk for weight gain six months after the completion of an 8-week ADF program.
It can help moderate glucose levels and fat metabolism
The food we eat is converted to glucose, which stays in the bloodstream for about two hours. If the body requires energy right away, it will use this immediately available source. After those two hours, any leftover glucose is converted and stored in the liver as glycogen. When the body looks for energy to utilize, it will first draw from the glucose in the bloodstream; if no glucose is available (for instance, if it has been more than two hours since we last ate), the body converts glycogen from the liver to use instead.
When glycogen stores have been exhausted, the body will start to burn fat. Reduced opportunities to consume food, and thus raise blood sugar, means more opportunity for the body to exhaust its storage, and instead burn fat.
This process can decrease fasting blood sugar levels by teaching the body to utilize its sugars more effectively. Check out the video below to see why.
It may be good for your heart
In addition to evening out fasting glucose levels, reducing how often you eat or how much you eat can also reduce total cholesterol, triglycerides, blood pressure and insulin, all of which can be precursors to heart disease and stroke if they’re not in a healthy range.
One study suggests that there may be similar mechanisms involved in building cardiovascular wellness with fasting, just as one might expect with regular exercise. When we exercise, we build cardiovascular health by stressing and testing the heart, lungs and circulatory system. Fasting places stress on these systems and forces them to get stronger in response in a similar way.
It may help prevent Alzheimer’s and other neurodegenerative diseases
The body constantly breaks down and disposes of old cells in every organ and tissue in the body. This process, known as autophagy (literally, ‘to self-devour’), plays a key role in many physiological processes and helps keep the body running. Think of it as taking out the trash so your kitchen can still be functional.
When autophagy is disrupted, nervous system tissue, including the brain, can be affected. While the mechanisms are still largely unknown, one thing scientists agree can help promote autophagy is food restriction. Limiting intake regulates autophagy in many organs, including the liver and the brain. A 2010 study showed that short-term fasting led to noticeable increases in neuronal autophagy--that means the brain was actively cleaning up and removing waste materials more effectively than when the subject was eating normally. Less waste material in the brain, specifically amyloid plaques that are linked to Alzheimer’s Disease, may mean a lower chance of developing neurological conditions or impairments.
What to Know Before You Try Intermittent Fasting
With all of these possibly life-changing benefits at the tip of your fork, should you dive into fasting right away?
While it can be a valuable tool and an interesting approach to explore, it’s important to ease your way in. If you’re thinking of trying out a form of intermittent fasting, do so by gradually reducing caloric intake over a few days to prime your body. Don’t jump straight from 2000 calories a day to 500 without a little warm-up. Make sure you pay attention to how you feel, stay hydrated, don’t over-exercise, and seek medical attention if you feel more than simply tired.
Also, fasting is ineffective without adequate nutrition. Using your limited calories to consume junk won’t be an effective method for weight loss or disease prevention. The mechanics and benefits of caloric restriction can only be useful to the body if the calories it does ingest are from whole, nutrient-dense foods. The body still needs to know it’s getting what it needs, so if you’re going to embark on a nutrition journey like intermittent fasting, make sure you’re making the most of those small meals on fast days. There are so many ways to approach clean eating based on your personal preferences and restrictions, so you may want to experiment to find out if intermittent fasting is right for you.
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*This post is provided for educational purposes only.