Intermittent fasting is currently one of the most popular diet and health trends. So what does it involve, and is it something you should try? You can practice intermittent fasting in several ways, which includes refraining from eating during certain times of the day. A recent New England Journal of Medicine study concluded that intermittent fasting benefits health, aging, and health conditions such as obesity, diabetes, cardiovascular disease, cancers, and neurologic disorders. Previously, the focus was on calorie restriction as many studies showed benefits for overall health, including aging.
Intermittent Fasting is Not the Same as Calorie Restriction
Calorie restriction and intermittent fasting are not the same. With calorie restriction, average daily caloric intake is reduced without malnutrition or deprivation of essential nutrients. The health benefits of calorie restriction (or reduced food availability) likely result from a passive reduction of damaging oxygen free radicals over a lifetime. On the other hand, intermittent fasting limits food intake during certain times of the day, week, or month. So, with intermittent fasting, daily calorie intake can remain the same. But often fewer calories are consumed because there is less time for eating.
The benefits are proposed to result from metabolic switching, meaning the body switches back and forth between using glucose for fuel and fatty acids (ketones). This is known as metabolic flexibility. These eating styles are still being studied as possible ways to maintain better health and longevity. They are not primarily intended as weight-loss plans. There are many different ways to practice intermittent fasting. Here are some of the most common approaches:
Overnight Fast
The overnight fast restricts eating for 12 hours (or slightly longer to 14 hours). Finish dinner by 7:00 p.m. and fast until 7:00 a.m. the following day, and you have completed the overnight intermittent fast. This is the easiest place to start for most people. (Sanoviv practices the overnight fast as part of the regular diet.)
The 5:2 Intermittent Fast
The 5:2 intermittent fast occurs with normal eating for five days of the week, and two days (non-consecutive) are fasting days, where only one meal is eaten (500 calories for women—600 calories for men). You choose the time to eat the one meal, and the time before and after it is considered the fasting period, during which only water, infused water, or herbal tea is consumed. This is the basic plan, but different variations exist to ease people into this style of fasting.
| Day 1 | Day 2 | Day 3 | Day 4 | Day 5 | Day 6 | Day 7 |
|---|---|---|---|---|---|---|
| Normal Eating | FAST (one 500-600 calorie meal) |
Normal Eating | Normal Eating | FAST (one 500-600 calorie meal) |
Normal Eating | Normal Eating |
Alternate-Day Fasting
The alternate-day fast is similar to the 5:2 style, except the fasting occurs every other day. Normal eating occurs in between.
Time-Restricted Eating
Another widely studied and practiced intermittent fasting style is the time-restricted approach, also known as the 16:8. This means you fast for 16 hours a day, restricting food consumption to an 8-hour window. Most people have been practicing this approach by skipping breakfast and eating regular meals between 12 and 8 p.m. However, breakfast is essential for some, so this approach can also work by eating regular meals between 7 a.m. and 3 p.m. and fasting for 16 hours afterward. Eliminating night eating may work better for some, and it does not have to be every day of the week.
Many other approaches are being studied and practiced. Intermittent fasting interventions can improve obesity, insulin resistance, dyslipidemia, hypertension, and inflammation. Although scientists do not fully understand the specific mechanisms, the beneficial effects involve metabolic switching and cellular stress resistance (where your cells can better handle their daily stressors). Should you try intermittent fasting, remember that this eating style is not for everyone, nor is it a short-term weight loss plan. Intermittent fasting is a lifestyle that is natural to the human body.
