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During the holidays, fasting may be the furthest thing from your mind. Once the Holidays are over, however, it may suddenly seem like an attractive option. Eating, as a basic activity of daily living, compensates for feelings of hunger and provides necessary nutrients to our physiological systems. Moreover, what we eat and how we eat can play a significant role in our health and well-being and may even impact longevity. Because of the significance of eating on well-being, diet interventions receive extensive attention in the media. Among different types of dietary interventions, fasting is emerging as the most significant; current research suggests that changing one’s eating habits by reducing caloric intake, when coupled with modifying meals schedules may delay or prevent the onset of many types of diseases and extend years of functionality to cells, tissues and organs.

Dr. Valter Longo, director of the USC Longevity Institute, has done numerous studies supporting the positive effects of fasting on longevity. The rationale of fasting to improve health can be explained, in part, by the Disposable Soma Theory, a major theory in  physiology of aging studies. This theory posits that the notion of senescence is the decrease in an organism’s ability to reproduce and causes a related increase in the chances it will die as it ages. It assumes that the body needs to budget and appropriate the energy for various tasks to maintain subsistence. In allocating energy for different physiological activities, there is a tradeoff between using it for reproduction or for cell, tissue or organ repair.

In other words, if a substantial proportion of available energy is used for growing new tissues, less energy will remain for reproduction, regeneration and repair of existing body components. When we eat less food, our systems may interpret this behavior as a signal that the energy acquired from digesting food is becoming scarce. Therefore, our body will adjust so as not to deplete remaining energy by using too much of the it for reproductive activities. Instead, the body will focus more on maintaining the function of existing tissues and wait for a more suitable time to reproduce. As a result, existing tissues will be better maintained and protected. In maintenance mode, our body systems, tissues and organs will be kept strong and healthy. That is a general explanation on how fasting can reduce morbidity and contribute to longevity.

Fasting refers to purposefully restricting one’s diet for a specific period. Traditionally, fasting was practiced in the manner of continuous caloric restriction, but the development of clinical trials and carefully designed programs have enriched our understanding of the effects of calorie-restricted fasting. Andrea Di Francesco, Clara Di Germanio, Michel Bernier, and Rafael de Cabo (2018) categorized fasting in four domains:

  1. Continuous Caloric Restriction: Reducing caloric intake by 15% to 40% every day during the fasting period can produce rapid results in weight loss. Continuous caloric restriction can contribute to protecting against obesity, diabetes, hypertension, cardiovascular disease, etc., if you are willing to give up some of your favorite foods for a specific time.
  2. Time-restricted Feeding: It means restricting eating time to a certain time-frame, usually a four to twelve-hour window during the fasting period. For example, from one perspective, we may consume food from 8 a.m. to 12 p.m. and not again until the next day. In some religious customs, there are clearly defined restrictions. For example, there is Post-Meridiem Fasting in Buddhism and, dawn-to-dusk fasting coupled with nightly feasts during Ramadan for Muslims. Recent research suggests that time-restricted feeding can help prevent type 2 diabetes, hypercholesterolemia, hepatic steatosis, etc.
  3. Intermittent or Periodic Fasting: Intermittent fasting means alternating 24-hour periods of fasting or a sufficiently low caloric diet, usually no more than 25% of energy needs, including 24-hour purposeful eating during the fasting period, while periodic fasting refers to fasting or using sufficiently low calories diet one to two days and then resuming to a five-day willful eating time frame during the fasting period. Both intermittent and periodic fasting can help delay or prevent obesity, hypertension, cardiovascular disease, oxidative stress, neurodegeneration, diabetes, to name a just few symptoms of illness and distress that may be positively affected, when performed under a doctor’s care.
  4. Fasting-mimicking Diets: It means decreasing caloric intake, usually 30% of energy needs, for five uninterrupted days and then going back to willful eating habits during the defined fasting period. The fasting-mimicking diet is usually practiced every three or four months a year. Experiments show that fast-mimicking diets can provide a defense against diabetes, cancer, etc., reduce the risks associated with several types of age-related diseases and promote longevity.

Human beings have practiced fasting and the unpleasant variance we know as starvation. However, because of their using unsophisticated medical technologies, the potential health benefits of fasting were not noted adequately. Today, fasting is receiving more attention and current scientific, social and economic developments make the health and beauty effects of fasting more attractive to consider. We have basic recommendations for those who may be considering one of these fasting options:

First, when deciding to practice fasting, take the time to do some research on possible negative outcomes. This will enhance your health literacy regarding fasting and possible consequences.

Second, before beginning a program of fasting, consult with a professional nutritionist on how best to proceed. For people who have no experience in fasting, suddenly being deprived of certain foods may be challenging; therefore, it is necessary to take a strategic approach to dieting to improve the odds of achieving diet goals.

Third, if it becomes impossible to tolerate the dietary restrictions, feel free to give up and restart when further motivated. The first few days of fasting could be difficult to bear. If the uncomfortable feelings have exceeded our level of tolerance, we should not feel guilty. Sometimes, one’s own body may recognize that to continue fasting may result in unintentional, negative consequences to our health and well-being. Often, we can back off for a period and restart fasting when we are so inclined.

Remember that unless approached systematically, after undertaking weight-loss dieting, the weight lost often comes back and, even worse, additional pounds may accrue without carefully maintaining diet guidelines.

If you have questions, or comments about this article, please contact the authors at usc.rxxlab@gmail.com.

Disclaimer: Persons with eating disorders should consult with a physician before considering any fasting diet.

Mengzhao Yan, MA, Senior Lab Assistant; Erin Crutcher, MSG Candidate, Research Assistant; George Shannon, MSG, PhD; Director, USC Rongxiang Xu Regenerative Life Science Lab (RxX Lab).

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