Often dismissed as a “fad”, intermittent fasting is not a new practice. People have been fasting for health, religious, and ritual reasons for centuries, and the evidence of such can be found in everything from religious texts to history books.
But despite the bad reputation it often gets, intermittent fasting has a myriad of health benefits, and plenty of science and experts to back them up. For many people, intermittent fasting has become the key to improving their health and maintaining a healthy weight.
What is Intermittent Fasting?
Intermittent Fasting (IF) is the practice of deliberately going without food for extended periods of time, usually on a set schedule, and then allowing for an “eating window”.
There are several schedules that intermittent fasters typically follow, including:
- 16/8 method – fasting for 14-16 hours a day with an “eating window” of 8-10 hours
- 5:2 method – eating normally 5 days a week, while restricting calories to 500-600 on two days of the week
- Alternate-day fasting – fasting every other day, sometimes allowing for 500 calories on fasting days
- Eat-Stop-Eat – doing a 24-hour fast, once or twice a week
- The Warrior Diet – fasting during the day, eating a huge meal at night
- Spontaneous Meal Skipping – skipping meals when it's convenient
Intermittent fasting is sometimes used alongside other diet or lifestyle changes. For instance, intermittent fasting works well with the keto diet and other low carb diets.
The Health Benefits of Intermittent Fasting
1. Weight Loss
One of the main reasons people try intermittent fasting is to lose weight. And according to research, it works.
Short-term fasting lowers insulin levels, increases growth hormone levels, and increases norepinephrine (noradrenaline) which all help the body more readily break down fat and use it for energy. Because of these changes in hormone functioning, short-term fasting can actually increase your metabolic rate by 3.6-14% (1).
In addition to boosting your metabolism, fasting also naturally reduces the amount of calories you consume. Some studies have shown that people actually eat 20% less on fasting days (2).
A review of the scientific literature on fasting in 2014 revealed that fasting often leads to a 3-8% decrease in weight over 3-24 weeks. It was also not uncommon for people to lose 4-7% of their waist circumference, indicating that harmful belly fat is reduced with fasting. In addition, intermittent fasting causes less muscle loss than continuous calorie restriction (1).
2. Decrease Risk of Health Conditions
Intermittent fasting may play a significant role in reducing risk of health conditions, and even help control chronic health conditions.
Although the exact outcomes of fasting on cardiovascular health have not been measured, several studies show improvements in heart health that seem promising (2). This includes an increase in levels of adiponectin (an anti plaque-forming and insulin-sensitizing protein hormone) and decreased levels of Leptin (a pro plaque-forming adipokine).
Intermittent fasting has also been associated with improvements in blood pressure, total and LDL cholesterol, blood triglycerides, inflammatory markers and blood sugar levels (1).
Other studies have found intermittent fasting to help reduce cholesterol levels in certain conditions, trigger stem cell regeneration, as well as benefit people with cardiovascular disease.
Finally, intermittent fasting may delay the onset of Alzheimer's disease or reduce its severity, as was found in a study done on rats (9). Case reports have also found significant improvement in symptoms of Alzheimer's in 9 out of 10 patients who followed a lifestyle intervention plan which included daily short-term fasts (8). Further animal studies show that fasting could possibly protect against neurodegenerative diseases such as Parkinson's and Huntington's disease (6,7).
3. Reduced Insulin Resistance
Several factors suggest that intermittent fasting can help reduce insulin resistance and therefore protect against or help control diabetes.
A dramatic restriction in calories (as with those who undergo gastric bypass surgery) has been shown to resolve diabetes in about 83% of patients. Intermittent fasting is thought to mimic these results (2).
Additionally, studies have found that intermittent fasting leads to an impressive reduction in blood sugar levels and improves insulin resistance. Some studies (on humans, yay!) have shown intermittent fasting to reduce blood sugar by as much as 3-6% and fasting insulin by as much as 20-31% (1).
Intermittent fasting induces a “waste removal” process at the cellular level in our bodies called autophagy. This process aids the body in breaking down cells and metabolizing dysfunctional proteins and buildup within cells.
Autophagy also protects against several diseases, including cancer and Alzheimer's disease (1).
5. Reduced Inflammation
It's believed that the basis of almost every chronic disease is inflammation and oxidative stress.
Studies have found that fasting induces a anti-inflammatory effect on the body. Reducing inflammation through fasting improves the nervous and immune systems (10).
Several studies have also shown that intermittent fasting enhances bodily resistance to oxidative stress (1).
6. Cancer Prevention
There is mounting evidence that intermittent fasting could protect against certain kinds of cancer as well as reduce the side effects of chemotherapy.
For instance, caloric restriction has been associated with up to a 55% reduction in the incidence of breast cancer. Some scientists believe that caloric restriction decreases cellular proliferation and angiogenesis (the creation of new blood vessels that feed cancer cells).
Furthermore, calorie restriction is associated with a significant anti-inflammatory effect on the body. This anti-inflammatory response may decrease cancer progression and malignant conversion. Studies have shown that a combination of intermittent fasting along with cancer treatment (chemotherapy or radiation) may increase the treatment's effectiveness (2).
Finally, fasting may reduce the various side effects of chemotherapy, especially when practiced immediately before and after treatment (1).
7. Extended Life Span
Although it hasn't been proven, many people believe, for good reason, that intermittent fasting can help humans live longer.
Animal studies also suggest that intermittent fasting can help people live longer. One study on rats found that intermittent fasting can extend lifespan in a similar way as caloric restriction (3, 4).
Another study found that rats who fasted lived 83% longer than rats who did not fast (5).
We now also know of the many health benefits of fasting. It can decrease chronic health conditions, repair cellular damage, reduce inflammation, and perhaps help prevent cancer. All of these things can help you live a longer and healthier life.