The Pluses and Minuses of Intermittent Fasting

Intermittent fasting is a form of eating pattern that involves time cycles of fasting and eating, and it may be the key to prolonging life. 

See more of our coverage on intermittent fasting.

Intermittent fasting does not focus on the diet, but rather on the pattern of eating. Previous studies have linked intermittent fasting to weight loss. In a study published in the 1997 Journal of Medicine, Weindruch & Sohal showed that decreasing the availability of food through a specified period has significant impacts on the health and aging process of animals. This paper delved deeper into the relationship between this form of eating pattern and the overall health of the human and animal body. Food eaten is broken down in the body through the various metabolic processes, affording the body the energy it needs to sustain its vital organs to keep on functioning. Intermittent fasting, also called calorie restriction, reduces energy produced for the body’s metabolic process. The body responds by shutting down unnecessary procedures and focusing on the primary operations, including tissue repair and maintenance.

The paper presents clinical findings from previous studies that focus on intermittent fasting and its effects on different aspects of health. Over the past 50 years, a vast majority of studies on health benefits of intermittent fasting have concluded that the life span of animals and humans is significantly increased in the event of intermittent fasting. The cellular response to a reduction in energy production in the body is to downregulate specific processes in the body. One such method is protein synthesis. The cell inhibits the Insulin-like Growth Factor 1 (IGF-1) signaling pathway, which results in the reduction of the number of amino acids in blood circulation. Intermittent fasting increases the levels of AMP for every ATP molecule in the cell. This results in the activation of the 5’ AMP-activated protein kinase (AMPK) whose primary function in the cell is to regulate the energy balance in the cell by activating glucose and fatty acid uptake and oxidation during fasting cycles.

During fasting, a characteristic metabolic switch takes place where the cell begins to use fatty acids as the primary source of energy. Glucose/carbohydrate is the main source of energy for the body. Intermittent fasting, which usually lasts for two days each week, uses up the free glucose for energy production and switches the metabolism into fatty acid-based energy production. The essence of the switch stems from the fact that oxidation of fatty acids and ketone bodies has a low respiratory exchange ratio.

A meta-analysis was done that incorporates data from studies done over 78 years, and showed that intermittent fasting results in an increase in the average lifespan of about 45%, but only 27% in mice. 41 Mice that had been inbred through DNA recombination expressed a high amount of variations, with some having significantly extended life spans while others died early. The differences were attributed to unaccounted for factors such as sex, environmental condition, and genetics. Intermittent fasting, when done together with regular exercise, builds up adaptations that enhance mental and physical health with increased resistance to diseases. A study done at the Wisconsin University published findings of improved health and mortality during intermittent fasting.  A study by the National Institute of Aging shows contrary results; intermittent fasting enhances health but does not reduce mortality.

Patients with obesity participated in a study where they subscribed to intermittent fasting over two months and consequently registered increased levels of ketone levels on  fasting cycles. The patients also lost weight over this period. Obesity usually presents itself with asthma as an accompanying condition, which in intermittent fasting was mitigated.

This review provides loopholes in the studies presented. Some studies contradicted other studies focusing on the same subject. This leads to an impasse where the data provided leaves more questions than it answers. Two contradicting studies raise the question of whether intermittent fasting reduces mortality.

Practice Pearls:

• Intermittent fasting is a form of fasting that follows cycles of not eating. The most used periods include two days of fasting each week.
• The body makes the necessary changes, like switching metabolism to the available metabolite and shutting down anabolic processes.
• These studies were done mostly on rats, mice, and other animals with varying degrees of success. The results of these studies need further testing and confirmation.

De Cabo R. & Mattson M. P. (2019). Effects of Intermittent Fasting on Health, Aging and Disease. N Engl J Med 2019; 381:2541-51. DOI: 10.1056/NEJMra1905136

Sandra Zaki, PharmD Candidate, Florida A&M University