Intermittent Fasting: A Review of Current Science
Overview of Intermittent Fasting
A recent review highlights the promising potential of intermittent fasting for weight loss and the reversal of various medical conditions. This review, authored by neuroscientist Mark Mattson, Ph.D., from Johns Hopkins Medicine, was published in The New England Journal of Medicine. It indicates that intermittent fasting can effectively aid in weight loss and combat obesity, diabetes, cardiovascular diseases, cancer, and neurodegenerative disorders without relying on synthetic medications.
Understanding Intermittent Fasting
Intermittent fasting involves alternating between periods of eating and extended fasting. While it may seem challenging in a culture accustomed to three meals and snacks daily, common fasting protocols include alternate-day fasting, the 5:2 method (fasting for two days each week), and daily time-restricted eating (such as fasting for 16 to 18 hours daily). Individuals may find it difficult to adopt this lifestyle due to societal norms surrounding food and constant exposure to food marketing. Initial side effects, such as hunger, irritability, and decreased focus, typically subside within the first month of practice.
The Metabolic Switch Induced by Fasting
Fasting is believed to trigger a metabolic switch, whereby the body shifts from utilizing glucose derived from the liver to burning fat from adipose tissue for energy. During fasting, fat is converted into fatty acids and glycerol, which the liver then transforms into ketone bodies. These ketone bodies serve as an energy source for cells and facilitate signaling processes that activate adaptive cellular pathways aimed at promoting survival. This response may enhance the body’s inherent defense mechanisms against oxidative stress and improve the repair of damaged molecules, while also conserving energy by minimizing synthesis, growth, and reproduction. The detailed mechanisms remain under investigation.
Health Benefits of Intermittent Fasting
According to Mattson, the periodic metabolic switch associated with intermittent fasting improves blood sugar regulation, stress resistance, and inflammation—key indicators of overall health. It has beneficial effects on cardiovascular health, influencing blood pressure, lipid levels, and resting heart rates in both humans and animals. However, individuals who frequently overeat or consume multiple meals daily may not experience these health benefits.
Growing evidence suggests that intermittent fasting effectively prevents obesity in both animals and humans and can reverse insulin resistance in individuals with prediabetes or type 2 diabetes, as demonstrated in recent studies. One study involving 100 overweight women on the 5:2 fasting regimen showed increased insulin sensitivity and reduced belly fat compared to those in a calorie-reduction group.
Numerous animal studies have indicated that alternate-day fasting may decrease the incidence of spontaneous tumors and inhibit the growth of induced tumors. While more research is needed to determine similar effects in humans, some case studies involving glioblastoma suggest that intermittent fasting could suppress tumor growth. However, the impact of fasting on cancer recurrence remains unclear.
Potential Impact on Neurodegenerative Diseases
Preclinical studies on alternate-day fasting in animals have reported delays in the onset and progression of Alzheimer’s and Parkinson’s diseases. Preliminary findings also suggest that intermittent fasting may alleviate symptoms of asthma in obese patients, improve rheumatoid arthritis symptoms in adults, and enhance surgical outcomes in animals.
Recent studies hint that intermittent fasting may positively influence various aspects of cognitive performance and brain health, including working memory in both animals and adults. Further studies are necessary to establish its effects on learning and memory, particularly in older adults and those with neurodegenerative diseases.
Conclusion
The review acknowledges that the long-term consequences of intermittent fasting remain to be fully understood, and the findings cannot be generalized beyond the studies included.
References
Effects of Intermittent Fasting on Health, Aging, and Disease | NEJM. (2020). Retrieved from https://www.nejm.org/doi/full/10.1056/NEJMra1905136
Hopkins Medicine. (n.d.). Intermittent fasting: live ‘fast,’ live longer? Retrieved from https://www.eurekalert.org/pub_releases/2019-12/jhm-ifl121819.php
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