The science behind intermittent fasting — and how you can make it work for you

Intermittent fasting is based on the idea that when you reduce your calorie intake for limited stretches of time, your body will use its stored fat for energy. Intermittent fasting has many health benefits, including losing weight.

There is no one way to do intermittent fasting. There is the 5:2 diet, which means eating very few calories for two days of the week, followed by five days of normal eating. Or the alternate-day fasting, which means eating normally for one day, then either nothing or just 500 calories the next.

One intermittent fasting method is known as time-restricted eating: A person consumes all of their calories for the day within an 8-to-12-hour window. You might eat breakfast at 8 AM, including coffee, and finishing your dinner by 6 PM.

In an experiment, two sets of mice were fed the same diet and ate the same number of calories a day. One set had access to food for 24 hours, and the other group had access for only 8 hours. After 18 weeks, the group that could eat all hours showed signs of insulin resistance and had liver damage. The mice who ate in an 8-hour window did not have the condition and weighed 28 percent less than the other group.

Many of the human body’s processes are tied to our circadian rhythms.

Eating food at the right time can nurture us, and healthy food at the wrong time can be junk food because it gets stored as fat instead of being used as fuel.

Time-restricted eating gives our body a chance to use up fat. When we eat, our body uses carbohydrates for energy. When we don't need them right away, they get stored in the liver as glycogen or converted into fat.

When we finish eating for the day, our body first use glucose from the carbohydrates we've eaten before moving on to the stored carbohydrates, or glycogen, in the liver. Glycogen lasts for eight hours after we've stopped eating. After that, our body begins to tap into its stored fat.

When we shorten the period for eating and extend the time for fasting, we stay in the fat-burning mode of our metabolism.

The moment we eat food, even coffee with a bit of sugar and milk, we switch to the other mode and start burning carbohydrates while storing glycogen and fat.

• Subjects in a study reported experiencing better sleep, more energy in the mornings, and less hunger at bedtime.
• In a study of men at risk for type-2 diabetes, after one week of restricting eating to a nine-hour window, the men showed a lower spike in blood glucose after a test meal.
• In another experiment of time-restricted eating, where the subjects were on medication to lower cholesterol, after 12 weeks, they found reduced cholesterol levels of about 11 percent on average.

• Only consume water during your fasting window. It means no coffee, tea, or herbal tea.
• Drink only plain hot water after waking up as it can give you the same soothing feeling as coffee.
• If you have to be very alert in the morning, it's OK to have black coffee, but don't add any creamer or sweeteners.
• Wait to eat breakfast until you've been awake for a few hours.
• Finish your last meal about two to three hours before your bedtime.

While the time-restricted eating holds promise, there is a need for more research.

• There haven't been studies with humans that lasted longer than a few months.
• The gut microbiome actually changes in mice that restrict their eating to an eight-hour window, so they digest nutrients differently. It remains to be seen if it is possible in humans.
• Research suggests that people practicing intermittent fasting eat more before and after their fasting days and don't receive calorie-reducing benefits.
• There may be a potential danger for people who struggle with binge-eating disorder or anorexia.