Highlights

  • During an extended fast, a period where no food is consumed, insulin and blood sugar levels decrease while other hormones like metabolism-promoting growth hormone increase, creating a state that triggers body fat metabolism.
  • Timing the intake of food is important to induce a fasting state, which has been associated with leaner body mass, increased fat loss, and a more regular and stable sleep-wake cycle (circadian rhythm).

For overweight and obese adults, excess body weight increases the risk of death. In fact, approximately one in six deaths in the US is related to being overweight. Moreover, losing modest amounts of weight has been associated with cardiovascular benefits like improved blood pressure and cholesterol readings. Several studies have linked moderate weight loss to a lower risk and incidence of diabetes in overweight adults. Since being overweight is associated with increased mortality risk and losing weight can decrease this risk by improving healthspan-related factors such as blood pressure and blood sugar, finding the most efficient weight loss technique, preferably one that primarily burns fat, is key.

Now, Andrew Huberman, a professor of neurobiology and ophthalmology at Stanford University, has presented a series of intermittent fasting techniques to efficiently burn fat in a YouTube video from one of his laboratory’s podcasts. In his YouTube segment, Dr. Huberman describes how prolonging the hours without eating after waking up can help one capitalize on the physiological benefits, like a propensity for fat burning, from a hormonally-regulated fasted state. Huberman says that anyone interested in using intermittent fasting to burn body fat can choose from a few different dietary schedules like going 16 hours per day without eating or eating regularly one day and then eating very few calories the next. Moreover, Huberman mentions human studies showing that intermittent fasting is safe and does not cause bone loss or detrimental metabolic abnormalities, which could make this dietary intervention an appealing way to lose weight and possibly extend healthspan.

“If I can emphasize anything today, it’s that what you eat and when you eat it set conditions in your body, and those conditions can be very good for you or very bad for you, depending on when you eat,” says Huberman.

Timed Feeding Can Propel Your Body into a Fasted State

Huberman says when you eat is as important as what you eat. Research shows that eating during the daytime, when we are most active, benefits lean body mass, fat loss, and confers a more regular and stable circadian rhythm. However, eating during the night, when we are least active, can be detrimental to our health.

Therefore, it is better to eat during the day and fast at night. Moreover, it takes five to six hours to enter a fasted state, because this is how long it takes for insulin and blood sugar to be removed from circulation after eating. Furthermore, we can speed up the clearance of blood sugar and insulin with light exercise after each meal. An easy example is going for a 20 to 30-minute walk after eating. Another point Huberman mentions is not eating at least two to three hours prior to bedtime.

If we are in a fasted state while we sleep, we will optimize autophagy — the destruction of damaged cells — which helps to preserve overall tissue function. Autophagy is a natural process that occurs mainly during sleep, although not only during sleep, according to Huberman. Intriguingly, fasting of any kind is believed to enhance autophagy.

Other Ways to Practice Intermittent Fasting

Dr. Huberman describes other intermittent fasting techniques, aside from going 16 hours per day without food, that include longer fasts of 24 hours, 36 hours, or more at a single time. He also says that some people prefer to do alternate-day fasting, which involves eating normally one day and then not eating at all the next. Another intermittent fasting technique entails eating regularly one day and eating very few calories (500 or 600 calories) the next. Yet another method includes eating enough calories to maintain adequate metabolism (about 1,200 calories for women and approximately 1,500 calories for men) for five days and then completely fasting for two days. Finally, another related dietary intervention is to eat very few calories per day (300 to 500 calories) on a consistent basis. One can engage in any one of these dietary schedules, all included under the umbrella designation of intermittent fasting.

(Intermittent Fasting Techniques | NMN.com) Intermittent fasting can be done with various eating schedules. Sixteen-hour restricted feeding involves eating only during an eight-hour window of elevated physical activity, while 24 and 36+-hour fasting encompasses fasting for these periods whenever possible. Moreover, alternate day fasting entails only eating every other day. Eating very few calories every other day is another intermittent fasting method. Eating enough calories to maintain normal metabolism and then fasting for two days can also be done, and another technique entails eating few calories (300 to 500 calories) consistently.

Huberman says that the alternate-day fasting technique has been looked at in a research study setting. Researchers studying this method of intermittent fasting found those who followed the every-other-day fasting dietary intervention did not suffer bone loss or other detrimental effects. According to Huberman, alternate-day fasting, in many cases, can produce more rapid weight loss effects and lower blood sugar levels more efficiently than standard time-restricted intermittent fasting (16 hours or more without food during a 24-hour cycle).

Huberman goes on to say that by following a time-restricted feeding schedule for 60 days or longer, there are metabolic changes that bias weight loss from fat tissue loss as opposed to loss of muscle tissue or sugars stored in muscle for energy. Thus, according to Huberman, engaging in intermittent fasting with calorie intake lower than what is required to maintain metabolism is the most scientifically-supported way to ensure that a significant portion of lost weight comes from burning body fat.

Using Intermittent Fasting to Burn Fat May Promote Healthspan with Remaining Questions on Lifespan

Huberman presents intermittent fasting as an efficient way to lose weight by biasing metabolism toward fat burning as opposed to burning other tissues and energy storage compartments like muscle or sugar stored in muscle. With weight loss associated with intermittent fasting, one may improve healthspan and possibly avoid the elevated risk of mortality associated with being overweight.

Along those lines, a human trial showed that fat mass decreased in males who underwent intermittent fasting along with resistance exercise training. Furthermore, research has associated intermittent fasting with improved blood fat (lipid) profiles and weight loss in overweight individuals. This dietary intervention’s beneficial effects pertaining to blood lipids and weight loss may help to improve mobility and quality of life in overweight or obese adults, two more aspects of healthspan.

Intriguingly, reducing calorie intake by 30% has been shown to significantly extend male mouse lifespan. While intermittent fasting does not necessarily require cutting back calorie consumption to this extent, some degree of calorie intake reduction is expected with an intermittent fasting schedule. As such, whether these findings in male mice apply to fasting humans remains questionable, and setting up a human study to measure intermittent fasting’s effects on lifespan would not be feasible due to cost and ethical constraints. At the same time, the clean bill of health that one intermittent fasting routine, namely, alternate day fasting, has received along with the lifespan benefits in male mice leave the question of whether intermittent fasting may extend human lifespan open for debate.