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Intermitted Fasting and Health: What Does Science Say?


Lifestyle-related diseases, such as obesity, dominate the top 10 leading causes of death worldwide, playing a devastating role in healthcare costs, quality and length of life. It’s no wonder people are looking for ways to prevent and reverse disease.

Fasting is not new to the scene: People have practiced it for thousands of years, in a variety of religions, cultures, and countries around the globe. But only recently have scientific studies been able to elucidate the many powerful health benefits it provides.

Types of fasting

There are two main fasting types, spanning anywhere from 8 hours to 7 days:

  1. Intermittent Fasting (IF): This type of fasting alternates regular, healthy eating days with fasting days. Typically, the fasting days are non-consecutive and range from 0 calories (water-only) up to 600 calories per day. Three common approaches are:
  • 5:2: 5 days of eating with 2 non-consecutive days of fasting.
  • Alternate-day fasting (ADF): Every other day of fasting.
  • Time-restricted eating (TRE): Though not always classified as a type of intermittent fasting, shortening your daily eating window to 8 to 10 hours while fasting the rest (16:8, or 14:10) may help reduce calories and gain similar metabolic benefits to other types of IF.
  1. Periodic Fasting: Regimens within this type of fasting vary, spanning 16 hours up to 5 to 7 consecutive days of fasting. Fasting days may be water-only or reduced-calorie.

Health benefits

There are several impressive benefits to intermittent fasting, including:

  • Increases weight loss: Obesity, a global epidemic, is estimated to affect 300 million people by 2025. Intermittent fasting, especially the alternate-day approach, shows comparable weight loss to daily calorie restriction, with an average loss of 3 to 7% body weight. A review of multiple studies found increased visceral (belly) fat loss with IF vs. daily calorie restriction. Most existing studies are short in duration, so longer and larger studies are needed.
  • Improves metabolism: Some intermittent fasting studies have shown improvements in cardiometabolic parameters like A1c, blood sugar, blood pressure, LDL cholesterol, and triglycerides. Animal studies show IF promotes improved heart rate, blood pressure, and heart rate variability. If someone sustains IF, it may lead to improved long-term cardiac health.
  • Encourages autophagy, anti-aging, and longevity: Dr. Valter Longo, a longevity and fasting researcher, reports that fasting stimulates stem-cell regeneration, metabolic health, adaptive cellular responses, DNA repair, and autophagy. Autophagy is the body’s natural “detox” process that cleans up and eliminates damaged cellular tissue and debris. These cellular changes influence longevity, lifespan, and quality of life, healthspan.
  • Improves inflammation and stress response: One small study of overweight participants with asthma experienced improved markers of inflammation, oxidative stress, asthma-related symptoms, and quality of life within 2 weeks of an 8-week alternate day fasting regimen. An animal study showed IF improved inflammatory pathways that helped preserve brain health.
  • Contributes to cancer prevention: With cancer as the second leading cause of death worldwide, researchers and patients continue to try to understand the factors that affect the disease. Periodic fasting lasting 2 days or longer has shown similar effectiveness as chemotherapy in delaying the progression of a variety of cancers while protecting healthy cells. In addition to cancer prevention, research has reported reductions in tumor growth in mice.

Risks

Since fasting involves significant calorie restriction or avoiding food altogether, healthcare professionals do not recommend it for those with malnutrition or eating disorders. If you are acutely ill, wait to fast until you feel better. If you are on medications, discuss this with your doctor first.

Recognized as generally safe for most people, intermittent fasting has few side effects. But, be prepared to feel hunger, fatigue, or both as your body adjusts to reduced calorie intake. If you feel unwell, stop fasting.

Track your fasting

There are a variety of metrics you may find helpful when fasting. You can do many from the comfort of your own home with readily available tools like blood meters, fitness watch trackers, and apps.

Check blood glucose, blood ketones, and heart rate regularly. Fasting apps like Simple, or Zero, can also help you identify your fasting and eating patterns over time.

Bottom line: Is IF for you?

For many people, intermittent and short-term fasting can be a powerful tool to help reduce overall calorie intake while preventing and reversing several lifestyle-related diseases through beneficial metabolic changes. Work with your doctor or dietitian to help you develop the fasting and dietary approach that’s right for you.

References:

Arumugam, T. V., Phillips, T. M., Cheng, A., Morrell, C. H., Mattson, M. P., & Wan, R. (2010). Age and energy intake interact to modify cell stress pathways and stroke outcome. Annals of neurology.

Barnosky, A. R., Hoddy, K. K., Unterman, T. G., & Varady, K. A. (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Translational Research.

Brandhorst, S., Choi, I. Y., Wei, M., Cheng, C. W., Sedrakyan, S., Navarrete, G., Dubeau, L., Yap, L. P., Park, R., Vinciguerra, M., Di Biase, S., Mirzaei, H., Mirisola, M. G., Childress, P., Ji, L., Groshen, S., Penna, F., Odetti, P., Perin, L., Conti, P. S., … Longo, V. D. (2015). A Periodic Diet that Mimics Fasting Promotes Multi-System Regeneration, Enhanced Cognitive Performance, and Healthspan. Cell metabolism.

Bray, G. A., & Macdiarmid, J. (2000). The epidemic of obesity. The Western journal of medicine.

Fung, J (2016). Longer fasting regimens - 24 hours or more.

Johnson, J. B., Summer, W., Cutler, R. G., Martin, B., Hyun, D. H., Dixit, V. D., Pearson, M., Nassar, M., Telljohann, R., Maudsley, S., Carlson, O., John, S., Laub, D. R., & Mattson, M. P. (2007). Alternate day calorie restriction improves clinical findings and reduces markers of oxidative stress and inflammation in overweight adults with moderate asthma. Free radical biology & medicine.

Mattson, M. P., Longo, V. D., & Harvie, M. (2017). Impact of intermittent fasting on health and disease processes. Ageing research reviews.

Tinsley, G. M., & La Bounty, P. M. (2015). Effects of intermittent fasting on body composition and clinical health markers in humans. Nutrition reviews.

Varady, K. A., Cienfuegos, S., Ezpeleta, M., & Gabel, K. (2022). Clinical application of intermittent fasting for weight loss: progress and future directions. Nature Reviews Endocrinology.

World Health Organization. Cancer.

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