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? There are several different ways you can practice intermittent fasting, which involves refraining from eating during certain parts of the day. A recent study in the New England Journal of Medicine concluded that intermittent fasting has benefits for health, aging, and health conditions, such as obesity, diabetes, cardiovascular disease, cancers, and neurologic disorders.1 Previously, the focus was on calorie restriction as many studies showed benefits for overall health, including aging. However, 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) are thought to result from a passive reduction of damaging oxygen free radicals over a lifetime. During intermittent fasting, on the other hand, food intake is limited 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 mainly 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. Both of 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:
- The overnight fast restricts eating for 12 hours (or slightly longer to 14 hours). Finish dinner by 7:00 pm and fast until 7:00 am the next morning 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 occurs with normal eating for 5 days of the week and 2 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 it and after it are considered the fasting periods, where only water, infused water, or herbal tea is consumed. This is the basic plan but there are different variations of this that 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 meal 500-600 calories) | Normal Eating | Normal Eating | FAST (one meal 500-600 calories) | Normal Eating | Normal Eating |
- Alternate day fasting is similar to the 5:2 style except the fasting occurs every other day. Normal eating occurs in between.
- Another widely studied and practiced intermittent fasting style is the time-restricted approach, also known at 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 their regular meals between 12 and 8 p.m. However, breakfast is important for some, so this approach can also work by eating regular meals between 7 am and 3 pm and fasting for 16 hours thereafter. Eliminating night eating may work better for some and it does not have to be every day of the week.
There are many other approaches that are being studied and practiced. In fact, intermittent fasting interventions can improve obesity, insulin resistance dyslipidemia, hypertension, and inflammation.2 Although scientists do not fully understand the specific mechanisms, the beneficial effects involve metabolic switching and cellular stress resistance (where your cells are better able to handle their daily stressors).3 Should you decide to try some intermittent fasting, keep in mind that this eating style is not for everyone, nor is it a short-term weight loss plan. Intermittent fasting is a lifestyle, one perhaps that is natural to the human body. References
- de Cabo, R. and M. P. Mattson (2019). “Effects of Intermittent Fasting on Health, Aging, and Disease.” N Engl J Med 381(26): 2541-2551.
- Redman, L. M., et al. (2018). “Metabolic Slowing and Reduced Oxidative Damage with Sustained Caloric Restriction Support the Rate of Living and Oxidative Damage Theories of Aging.” Cell Metab 27(4): 805-815 e804.
- Mattson, M. P. and T. V. Arumugam (2018). “Hallmarks of Brain Aging: Adaptive and Pathological Modification by Metabolic States.” Cell Metab 27(6): 1176-1199.
