It’s every dieter’s dream: imagine being able to eat whatever you want most days of the week, limiting your intake for one or two days at a time and still losing weight. Believe it or not, intermittent fasting benefits more than just your waistline; crucially, fasting helps to stabilize blood sugar levels, reduce inflammation and keep your heart healthy.
There are a variety of approaches to intermittent fasting and many studies backing the multitude of benefits to your health and overall wellness.
From fasting for just a few hours each day to skipping meals for two days each week, intermittent fasting (IMF) can be an easy way to simultaneously improve your health and achieve your weight loss goals.
Intermittent fasting, also known as cyclic fasting, has risen in popularity in recent years as more and more research emerges discovering new intermittent fasting benefits.
In a 2016 Cell Metabolism study called “Fasting, Circadian Rhythms, and Time-Restricted Feeding in Healthy Lifespan,” the authors discuss how fasting allow humans to rely less on our glucose stores for energy and instead on our ketone bodies and fat stores. As a result, “both intermittent and periodic fasting result in benefits ranging from prevention to the enhanced treatment of diseases.” (1) Even fasting mimicking diets (FMDs), which is not true fasting, can create beneficial changes similar to those caused by fasting.
However, intermittent fasting is hardly a new concept. It’s been used for centuries during times when food was scarce and it even plays a central role in many major religions. In fact, once a year, Muslims observe Ramadan, a month of fasting from dawn until sunset.
It’s difficult to define intermittent fasting as there’s not just one correct method for how to fast. In fact, there are many different variations of intermittent fasting that are used around the world. Each follows a different eating pattern that is often strictly adhered to in order to achieve physical or even spiritual results.
How does it work? The extensive research on the concept of intermittent fasting suggests it functions in two different ways to improve various facets of health. First, intermittent fasting results in lowered levels of oxidative stress to cells throughout the body.
Second, practicing fasting improves your body’s ability to deal with stress at a cellular level. Intermittent fasting activates cellular stress response pathways similar to very mild stressors, acting as mild stimulants for your body’s stress response. As this occurs consistently, your body is slowly reinforced against cellular stress and is then less susceptible to cellular aging and disease development. (2, 3)
The most common types of intermittent fasting — or fasting diets, as some call them — include:
One of the major intermittent fasting benefits is its ability to rev up fat burning and help the pounds slide off. In fact, many people prefer intermittent fasting to traditional diets because it doesn’t require you to meticulously measure your foods and track the calories and grams consumed.
IMF results in increased fat burning and fast weight loss by forcing your body to use up fat stores as fuel. When you eat, your body uses glucose (sugar) as its primary source of energy and stores whatever is left over as glycogen in your muscles and liver.
When you don’t give your body a steady stream of glucose, it begins breaking down the glycogen to use as fuel. After the glycogen has been depleted, your body seeks out alternative sources of energy, such as fat cells, which it then breaks down to help power your body.
This is similar to the ketosis diet (or “keto diet”), in which you deprive your body of carbohydrates and force it to use up stored fat for energy.
A 2015 review looked at the effects of alternate-day fasting on body composition and found that, on average, it slashed body weight by up to 7 percent and cut body fat by up to 12 pounds. Whole-day fasting led to similar results, but with up to a 9 percent reduction in body weight. (4) It’s less clear what whole-day fasting does to your valuable muscle stores.
Another study focused on the 16/8 method of intermittent fasting showed that it significantly reduced fat mass while retaining both muscle mass and strength. (5) This fact is why I recommend this style of intermittent fasting the most.
When you eat, carbohydrates are broken down into glucose (sugar) in your bloodstream. A hormone called insulin is responsible for transporting the glucose out of the bloodstream and into the cells where it can be used up as energy.
Insulin doesn’t always work effectively when you have diabetes, which can result in high blood sugar levels coupled with symptoms like fatigue, thirst and frequent urination.
Some studies have found that intermittent fasting benefits your blood sugar levels by keeping them well-regulated and preventing spikes and crashes.
In one study, participants with diabetes fasted an average of 16 hours daily for two weeks. Not only did intermittent fasting cause weight loss and a decrease in caloric intake, but it also helped significantly reduce blood sugar levels. (6)
Another study showed that fasting decreased blood sugar by 12 percent and also lowered insulin levels by nearly 53 percent. Preventing a build-up of insulin allows it to work more efficiently and keeps your body sensitive to its effects. (7)
One of the most impressive intermittent fasting benefits is its favorable effect on heart health. Studies show that intermittent fasting improves your heart health by lowering certain heart disease risk factors.
In one study, fasting was shown to influence several components of heart health. It increased good HDL cholesterol and decreased both bad LDL cholesterol and triglyceride levels. (8)
One animal study in the Journal of Nutritional Biochemistry showed that intermittent fasting caused an increase in levels of adiponectin. (9) Adiponectin is a protein involved in the metabolism of fat and sugar that may be protective against heart disease and heart attacks. (10)
In fact, in one study, rats who fasted every other day were nearly 66 percent more likely to survive a heart attack than those on a normal diet. (11)
Inflammation is a normal immune response to injury. Chronic inflammation, on the other hand, can lead to chronic disease. Some research has even linked inflammation to conditions like heart disease, diabetes, obesity and cancer. (12)
A study published in Nutrition Research followed 50 individuals observing Ramadan and showed that they had decreased levels of some inflammatory markers during Ramadan fasting. (13) Another study in 2015 found that a longer duration of nighttime fasting was associated with a decrease in markers of inflammation. (14) In the journal Rejuvenation Research, alternate-day fasting helped reduce markers of oxidative stress. (15)
While more research is needed, these studies provide promising evidence showing that IMF may help reduce inflammation and fight off chronic disease.
In addition to keeping your heart healthy and warding off disease, some studies have indicated that intermittent fasting protects the health of your brain.
One animal study showed that intermittent fasting helps enhance cognitive function and protect against changes in memory and learning function compared to a control group. (16) Another animal study found that intermittent fasting protects the brains of mice by influencing certain proteins involved in brain aging. (17)
Additionally, the anti-inflammatory effects of intermittent fasting may also help slow the progression of neurodegenerative disorders like Alzheimer’s disease. (18)
Some also say that fasting promotes autophagy, or “self-eating,” which is our normal bodily process of cellular renewal — a process that is supposedly aided by fasting, though more scientific evidence is needed until this is certain.
Leptin, also known as the satiety hormone, is a hormone produced by the fat cells that helps signal when it’s time to stop eating. Your leptin levels drop when you’re hungry and increase when you’re feeling full.
Because leptin is produced in the fat cells, those who are overweight or obese tend to have higher amounts of leptin circulating in the body. However, too much leptin floating around can cause leptin resistance, which makes it harder for it to effectively turn off hunger cues.
One study with 80 participants measured leptin levels during intermittent fasting and found that levels were lower at night during the fasting period. (19)
Lower levels of leptin could translate to less leptin resistance, less hunger and potentially even more weight loss.
As described above, there are many types of IMF with different options that can fit any schedule or lifestyle. It’s best to experiment and find the one that works best based on your individual needs.
For beginners, the easiest starting point is the intermittent fasting 16/8 method, a form of time-restricted eating. This typically just involves skipping your evening snack after dinner and skipping breakfast the next morning as well.
If you don’t eat anything between 8 p.m. and 12 p.m. the next day, for instance, you’ve already fasted for 16 hours.
Keep in mind that intermittent fasting should be viewed as a change in lifestyle rather than a diet. Unlike typical diets, there’s no need to count points or calories or plug your foods into a food diary each night.
To reap the most intermittent fasting benefits, make sure to focus on filling your diet with healthy whole foods during the days that you do eat to squeeze as many nutrients as possible into your day.
Additionally, always listen to your body. If you feel weakness or fatigue when you go an entire day with no food, try increasing your intake a bit and have a light meal or snack. Alternatively, try out one of the other methods of intermittent fasting and find what works for you.
Although intermittent fasting benefits many different aspects of health, it may not be ideal for everyone and some people may actually want to avoid IMF.
If you suffer from low blood sugar, for example, going without eating all day may lead to dangerous drops in blood sugar causing symptoms like shakiness, heart palpitations and fatigue. If you have diabetes, it’s best to work with your doctor to determine if intermittent fasting is right for you.
If you have a history of eating disorders, this may also not be ideal for you as it may encourage unhealthy behaviors and trigger symptoms. If you are a child or teenager and still growing, intermittent fasting is not recommended either.
Those who are sick may also want to reconsider intermittent fasting as it can deprive your body of the steady stream of nutrients that it needs to heal and get better.
Intermittent fasting for women? Of course, those who are pregnant should also avoid intermittent fasting and focus instead on a nutritious diet rich in vitamins and minerals. And certain women may encounter hormone issues if they intermittent fast for days on end — they may benefit from intermittent fasting only a few days a week rather than every day, for example.
Additionally, if you have gallstone disease, fasting may actually increase the risk of gallbladder problems and should be avoided.
Finally, studies show that fasting may alter the levels of your thyroid hormones. If you suffer from any thyroid issues, you may want to reconsider intermittent fasting to avoid alterations in these important hormones. (20)
If you’re physically active, intermittent fasting and working out is okay. While you can exercise during fast days, don’t push yourself too hard and remember to drink plenty of water. If you’re fasting for longer than 72 hours, however, it’s advisable to limit physical activity.