7 Science-Based Benefits of Intermittent Fasting
Diet plans and eating patterns come and go in popularity, but intermittent fasting may have staying power. Why? It is a simple plan that doesn’t require a lot of tracking or purchasing specialized ingredients or products.1
Intermittent fasting, or time-restricted eating, is an eating pattern that cycles between periods of fasting and eating. Plans vary based on the fasting length and cycle length.
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The two most well-studied intermittent fasting approaches include:2
- Time-restricted eating: eating within an 8- to 12-hour window and fasting or drinking only water or calorie-free tea or coffee the other 12 to 16 hours in a 24-hour block.
- Intermittent calorie restriction: cycling between calorie restriction and a more typical dietary intake. Examples include alternate-day fasting, 4:3 (eating: fasting), and 5:2 day plans. On fasting days, consumption is limited to 20% to 25% of energy needs.
Humans, along with most organisms, have an intrinsic circadian rhythm that regulates metabolic function in anticipation of predictable changes in light, temperature, and nutrient availability. Time-restricted eating is thought to support circadian rhythms and improve overall health.3
Weight loss and fat loss
Intermittent fasting can help with weight loss and fat loss because eating is restricted to a shorter window unless you eat more calories than typical during your eating window. Beyond this, time-restricted feeding increases fat breakdown and facilitates fat use by increasing the expression of genes involved in fat metabolism.3
Thirteen clinical trials compared intermittent fasting to daily calorie restriction, and 11 reported similar weight loss, whether using intermittent fasting or daily calorie restriction. A 5:2 and 12-hour time-restricted eating plan resulted in significant body fat reduction compared to daily calorie restriction.1
In a small 22-day study using alternate-day fasting, participants lost a mean of 2.5% body weight.4
In another study, 139 participants with obesity used time-restricted eating (8 hours) with calorie restriction or daily calorie restriction alone for a year. Researchers reported no difference in body weight, body fat, or metabolic risk factors between time-restricted eating and daily calorie restriction. However, the mean weight loss among participants was an impressive 8 kg (17.6 pounds).5
A systematic review of 40 studies found that participants using intermittent fasting lost between 7 and 11 pounds over ten weeks.6
Intermittent fasting seems to be effective for weight loss, as long as calories are not increased during the eating window to compensate.
Increased insulin sensitivity
When you eat, your blood sugar increases, and your pancreas secretes more insulin. Insulin ushers blood glucose into your body cells, where it can be used for energy. Simple sugars cause a higher spike in blood glucose and insulin than complex sugars, fats, and proteins.
After a meal, your body will continue to use the nutrients from your last meal for several more hours. This means that the “fed” state extends about three to six hours past your last meal.
Once your body passes from the “fed” state to the “fasting” state, it uses stored glycogen and then eventually ketones made in the liver as an energy source.
In nine clinical trials, fasting was associated with the following results:4
- 7 of 9 studies reported significant weight loss.
- 3 of 6 studies reported significant decreases in insulin levels.
- 1 of 6 studies reported a decrease in fasting glucose levels.
Alternate-day fasting seems to result in the most weight loss and reduction in glucose and insulin concentrations, but it is not practical for most people due to the intense hunger experienced on fasting days.5 Longer periods of fasting are associated with increased insulin sensitivity.
May improve liver health
Intermittent fasting improves liver health by changing liver enzyme levels, especially by reducing HNF4-alpha protein levels. HNF-4 alpha increases inflammation.7
Time-restricted feeding reduces liver fat, which also reduces inflammation in the body. When the liver has constant access to free fatty acids, it is more susceptible to excess oxidative stress because it contains less reduced glutathione. Glutathione is a powerful antioxidant.3
Prolonged periods of eating can also increase inflammation.7 Caloric excess is linked to systemic low-grade chronic inflammation, which can increase your risk for metabolic syndrome, non-alcoholic fatty liver diseases (NAFLD), type 2 diabetes mellitus, atherosclerosis, and cardiovascular disease.
Intermittent fasting and calorie restriction can reduce inflammation, reducing your risk for metabolic and age-related diseases.8
May improve heart health
Intermittent fasting reduces body weight and improves overall metabolism. However, even when body weight is maintained, it also decreases insulin resistance, oxidative stress, inflammation, and blood pressure. All of these benefits can improve heart health.3
The liver produces about 20% of all cholesterol and also regulates cholesterol breakdown. Dietary intake patterns and clock genes affect cholesterol synthesis and breakdown.9
In nine clinical trials, fasting was associated with the following results:4
- 3 of 8 studies reported significant improvements in low-density lipoproteins (bad cholesterol) or triglycerides.
- 3 of 6 studies reported significant improvements in inflammatory markers, including C-reactive protein (CRP), tumor necrosis factor-α (TNF-α), adiponectin, leptin, and brain-derived neurotrophic factor (BDNF).
Shift workers are at increased risk for cardiovascular disease, which has led to increased interest in the circadian rhythm of heart health. More research is needed to understand the relationship between feeding patterns, circadian rhythm, and cardiovascular disease.9
Supports cellular repair processes
Autophagy is a natural process in which your body removes damaged or dysfunctional cell parts and recycles them to repair other cells.
Autophagy declines with age and can be upregulated under certain physiological conditions, such as when fasting. In some studies, dietary restriction has been shown to extend lifespan and reduce risk for age-related diseases such as diabetes, cancer, and cardiovascular disease.
Researchers are investigating the potential effects of calorie restriction and intermittent fasting on cancer risk and response to treatment. Several small studies have shown fasting improves a patient’s response to cancer-treating drugs and decreases side effects.10,11
Intermittent fasting has the potential to reduce cancer risk, improve response to chemotherapeutic agents, and reduce medication side effects.
Understanding the factors that support autophagy has important anti-aging implications.
May improve brain health
Intermittent fasting can support brain health by promoting the production of brain-derived neurotrophic factor (BDNF). This factor supports the growth of new brain cells and protects against neurodegenerative diseases.
Intermittent fasting can enhance cognition and muscle performance. In animal models, intermittent fasting protected against brain cell dysfunction and damage due to stroke, epilepsy, traumatic brain and spinal cord injury, Alzheimer’s disease, and Parkinson’s disease.12
Supports a healthy gut microbiome
Depending on your circadian rhythm and feeding schedule, your gut has a daily rhythm for producing saliva, gut hormones, digestive enzymes, and bile salt. Gut muscle contraction and digestion also vary throughout the day, with decreased gut activity at night.
The relative concentrations of bacteria in the gut microbiome vary throughout the day and night. Animal studies indicate that time-restricted feeding reduces the relative amounts of gut microflora that increase obesity risk while increasing obesity-protective microflora.13
Time-restrictive feeding may also affect clock genes that impact the gut’s mucosal lining and reduce bacteria associated with mucosal damage and poor intestinal function.14 However, more research is needed to understand the potential benefits of time-restrictive eating for reducing bowel disease risk.
More studies are needed to evaluate the benefits of intermittent fasting and investigate its potential long-term effects, especially when using more extreme dietary patterns such as alternate-day fasting. These long-term effects may include low blood sugar, damage to the digestive system, and compromised bone metabolism.6 However, research suggests that intermittent fasting has many health benefits. It can also reduce stress, improve mental clarity, and reduce eating decision fatigue.
The longer you are in a fasting state, the higher your glucagon-like peptide (GLP1) hormone levels will be. This increase is primarily to regulate glucagon release from your pancreas. By inhibiting its release, GLP-1 hormones prevent excess glucose production and maintain steady fasting blood glucose levels. Semaglutide is a GLP-1 receptor agonist. In addition, semaglutide modulates your appetite, reduces hunger, delays stomach emptying, and makes it easier to lose weight.
If you are looking for effective weight-loss treatment options, talk to one of the treatment specialists to learn more about weight-loss options, such as semaglutide, a prescription medication used to treat obesity.
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While we strive to always provide accurate, current, and safe advice in all of our articles and guides, it’s important to stress that they are no substitute for medical advice from a doctor or healthcare provider. You should always consult a practicing professional who can diagnose your specific case. The content we’ve included in this guide is merely meant to be informational and does not constitute medical advice.
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2. Ezzati A, Rosenkranz SK, Phelan J, Logan C. The Effects of Isocaloric Intermittent Fasting vs Daily Caloric Restriction on Weight Loss and Metabolic Risk Factors for Noncommunicable Chronic Diseases: A Systematic Review of Randomized Controlled or Comparative Trials. J Acad Nutr Diet. 2023 Feb;123(2):318-329.e1. doi: 10.1016/j.jand.2022.09.013. Epub 2022 Sep 17. PMID: 36126910.
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8. de Groot, S., Pijl, H., van der Hoeven, J.J.M. et al. Effects of short-term fasting on cancer treatment. J Exp Clin Cancer Res 38, 209 (2019). https://doi.org/10.1186/s13046-019-1189-9
9. Hatchwell, L., Harney, D.J., Cielesh, M., Young, K., Koay, Y.C., O’Sullivan, J.F., Larance, M., 2020. Multi-omics Analysis of the Intermittent Fasting Response in Mice Identifies an Unexpected Role for HNF4α. Cell Reports 30, 3566–3582.e4.. https://doi.org/10.1016/j.celrep.2020.02.051
10. Jordan S, Tung N Casanova-Acebos M et al. Dietary Intake Regulates the Circulating Inflammatory Monocyte Pool. Cell, Volume 178, Issue 5, 1102 – 1114.e17
11. Mattson, M., Moehl, K., Ghena, N. et al. Intermittent metabolic switching, neuroplasticity and brain health. Nat Rev Neurosci 19, 81–94 (2018). https://doi.org/10.1038/nrn.2017.156
12. Rangan, P., Choi, I., Wei, M., Navarrete, G., Guen, E., Brandhorst, S., Enyati, N., Pasia, G., Maesincee, D., Ocon, V., Abdulridha, M., & Longo, V. D. (2019). Fasting-Mimicking Diet Modulates Microbiota and Promotes Intestinal Regeneration to Reduce Inflammatory Bowel Disease Pathology. Cell reports, 26(10), 2704–2719.e6. https://doi.org/10.1016/j.celrep.2019.02.019
13. Chaix A, Manoogian ENC, Melkani GC, Panda S. Time-Restricted Eating to Prevent and Manage Chronic Metabolic Diseases. Annu Rev Nutr. 2019 Aug 21;39:291-315. doi: 10.1146/annurev-nutr-082018-124320. Epub 2019 Jun 10. PMID: 31180809; PMCID: PMC6703924.