Intermittent fasting includes a variety of eating patterns that involve regular periods of fasting interspersed with normal meals.
One of the most popular health trends in recent years, intermittent fasting is a strategy successfully used by many people to improve health and lose weight.
It may even contribute to a longer life span. (1)
The eating patterns of intermittent fasting are nothing new; historically speaking, humans have always engaged in intermittent fasting, sometimes by choice, and other times by necessity.
Our ancestors ate when they could find food, and the human body is well-adapted to going without meals; biological changes take place to provide fuel for energy, and some of these changes have positive effects on health and wellness.
In more recent history, fasting has been an integral aspect of many religious practices, including Buddhism and Christianity.
We’ll cover the basics of intermittent fasting, outlining some of the most common approaches as well as the physiological changes you can expect if you decide to try it.
Flexible Eating Patterns Are Easy to Customize
We’re all a little different when it comes to appetite and normal eating patterns, and many people engage in intermittent fasting without even realizing it.
For example, skipping a meal now and then is a form of intermittent fasting; you may be a regular breakfast skipper, someone who just doesn’t get hungry until later in the day.
It’s simple to capitalize on habits you already have, and not as hard as you might think to institute a new practice to take advantage of the benefits you can realize from intermittent fasting.
The most common reason people choose to do intermittent fasting is weight loss, and it can be a very effective tool for weight control. (2)
These are the three most popular eating patterns:
- The “16/8” plan works well for many people because you never go longer than 16 hours without eating. All food is consumed during an eight-hour window; this could be whichever part of the day you’re usually most hungry.
- The “Eat-Stop-Eat” approach involves spending 24 hours without eating, usually once or twice weekly. A common way to do this is to forgo solid food from dinner one night until dinner the next evening.
- The “5:2 Diet” is also very popular; you eat every day, but on two non-consecutive days of the week, you only have between 500 and 600 calories.
Several other plans have also been popular on the intermittent fasting scene, and one of these might appeal to you:
- “Alternate Day Fasting” is exactly what it sounds like: you eat every other day. Some versions allow a minimal amount of calories on off days.
- The “Warrior Diet” calls for fasting all day (or eating only small amounts of raw vegetables or fruits during the day) and consuming a large meal in the evening during a 4-hour window. This is patterned after the custom of warriors who fought on an empty stomach and ate at night.
- Meal-skipping on a spontaneous basis is also used effectively as intermittent fasting. When it’s convenient not to eat, you don’t eat.
Biological Effects of Intermittent Fasting
A wide variety of benefits result when you abstain from eating solid food for varying periods of time.
Hormonal activity changes in order to make stored fat accessible as fuel for normal energy requirements, stimulating a series of positive alterations in physical processes.
- Levels of human growth hormone (HGH) increase dramatically, facilitating muscle gain and fat loss at the same time. (3, 4, 5, 6)
- Insulin sensitivity increases as insulin levels drop, which also contributes to burning fat for fuel. (7)
- Repairs at cellular levels are initiated, including autophagy, when old proteins that have built up in the cells are digested by healthy cells, removing dysfunctional waste matter. (8, 9)
- Gene expression is altered, potentially increasing longevity. Changes in genes can help protect against disease and aging processes. (10, 11)
When you’re eating less food, weekly caloric intake drops significantly, so intermittent fasting sets up automatic calorie reduction. The key is to avoid overeating between fast periods.
While extended fasting periods drop metabolic rates to conserve energy, intermittent fasting can bump up metabolism by anywhere from 3.6 to 14%. (12, 13) So you eat less and burn more, the perfect equation for dropping excess weight.
One review study showed that over periods from 3 to 24 weeks, subjects lost between 3% and 8% of body weight, an impressive figure that beats most diets. Participants also reduced waist measurements by 4% to 7%, indicating a decrease in harmful belly fat. (14)
There also appears to be less muscle mass loss with intermittent fasting than more traditional weight-loss strategies. (15)
Other Health Benefits
As mentioned above, insulin levels are affected by intermittent fasting, which can reduce the risk of developing type 2 diabetes.
The potential for decreasing the risk of developing heart disease also exists through engaging in intermittent fasting.
- Lower blood sugar levels
- Decreased insulin resistance
- Lower levels of inflammation
- Reduced blood triglycerides
- A reduction in LDL cholesterol measurements.
Animal studies indicate the protocol may also be useful in the prevention of Alzheimer’s disease. (26)
Intermittent Fasting is Not For Everyone
The safety factor for intermittent fasting is well established, and the only real side effect is hunger, although some people also experience muscle weakness.
Women have reported cessation of menstrual periods during intermittent fasting, but cycles normalized after they returned to regular eating. If you have trouble with irregular periods, you may want to steer clear of any type of fasting.
Using this approach isn’t advisable for children, anyone who is underweight, pregnant, breastfeeding, or trying to conceive. Those with the following medical conditions may want to avoid it as well:
- Low blood pressure
- Blood sugar regulation issues, including diabetes
- A history of eating disorders
- Taking prescription medications to control symptoms of any disorder
One version or another of intermittent fasting is very effective for some people, while others find it extreme and unmanageable. Identifying the plan that fits your schedule and physical requirements is often the key.
Summary: Intermittent fasting has a range of health benefits including weight loss, beneficial hormonal changes, and positive effects on risk factors for chronic diseases. If you have no contraindications and want to give it a try, test out some eating patterns until you find one that works for you, and enjoy the results.