Intermittent fasting (IF) consists of alternating between periods of abstaining from eating and periods of eating regularly. First popularized in 2012, by Dr. Michael Mosley’s TV documentary Eat Fast, Live Longer¹, the diet has long been associated with weight loss and improved health. While there are studies that assert this claim, there are others that suggest people ought to proceed with caution with this fasting. In this article, we’ll dive into the science behind IF, its proven benefits, potential risks, and how to safely practice it.
How Does Intermittent Fasting Work?
When we eat, our body breaks down food into simple molecules that can be easily absorbed. As for carbohydrates, our bodies break them down into sugar to use for energy, and anything not used is stored in fat cells. This process of storing sugar as fat cells requires insulin. Between meals, our insulin levels drop causing our fat cells to release sugar to use as energy, resulting in weight loss. Intermittent fasting takes this to another level by allowing insulin levels to drop so low that people not only burn sugar but also fat. Still, IF works differently for different people, and there are many ways to practice it.
Some common forms of intermittent fasting² include:
- 12-hour fasting
- 16-hour fasting
- Fasting twice a week
- Alternate day fasting
- 24-hour fasting (Eat-Stop-Eat)
- Meal skipping
- The Warrior Diet
Research¹ suggests that not all forms of IF are created equally. Nonetheless, some have shown to be very effective and sustainable, even more so when combined with a Mediterranean or plant-based diet.
Studies show that fasting for 10-16 hours³ allows the body to convert fat into energy, resulting in ketones being released into the bloodstream, encouraging weight loss. Additionally, a study examining alternate day fasting⁴ found that it can improve heart health and boost weight loss in both healthy and overweight adults. In addition, research indicates that fasting can improve verbal memory in adults⁵. Moreover, intermittent fasting has been linked to anticancer effects because it stimulates cellular autophagy, a natural process in which the body cleans out damaged cells. In vitro and in vivo studies illustrate that fasting can help improve the chemotherapeutic response⁶ in various types of cancer including, breast, colon, pancreatic, and lung among others.
Is Intermittent Fasting Safe?
Although there are benefits associated with some types of intermittent fasting, extreme forms such as The Warrior Diet have proven to be challenging for some individuals. Because the Warrior Diet only has a 4-hour eating window and requires nocturnal eating, it runs the risk that people will miss out on vital nutrients like fiber, potentially leading to digestive and immune health issues. IF is not recommended⁵ for:
- People under the age of 18
- Pregnant or breastfeeding women
- Individuals with blood sugar issues or diabetes
- Anyone with a history of eating disorders
Some common side effects of intermittent fasting include headaches, digestive problems, changes in mood, lack of energy, trouble sleeping⁷, dehydration, and malnutrition.
Tips to Practice Intermittent Fasting Safely
For your safety, you should speak to your physician before you begin any diet, including fasting. Be really cautious with this diet, as it is not suitable for everyone and can lead to health issues for some individuals. If you choose to practice intermittent fasting, you must stay hydrated and drink plenty of water or electrolytes throughout the day. Furthermore, remember to take time to rest and avoid any strenuous activity on days that you fast. On days that you are eating, make smart choices: choose nutrient-dense and high-volume foods to give your body the nourishment it needs. Finally, remember not to obsess over food and seek professional help to plan your days.
- Tello, Monique. “Intermittent Fasting: Surprising Update.” Harvard Health, Harvard Medical School, 10 Feb. 2020, www.health.harvard.edu/blog/intermittent-fasting-surprising-update-2018062914156.
- Leonard, Jayne. “Seven Ways to Do Intermittent Fasting: The Best Methods.” Medical News Today, MediLexicon International, 16 Apr. 2020, www.medicalnewstoday.com/articles/322293#seven-ways-to-do-intermittent-fasting.
- Collier, Roger. “Intermittent Fasting: the Science of Going Without.” CMAJ : Canadian Medical Association Journal = Journal De L’Association Medicale Canadienne, Canadian Medical Association, 11 June 2013, www.ncbi.nlm.nih.gov/pmc/articles/PMC3680567/.
- Varady, Krista A, et al. “Alternate Day Fasting for Weight Loss in Normal Weight and Overweight Subjects: a Randomized Controlled Trial.” Nutrition Journal, BioMed Central, 12 Nov. 2013, www.ncbi.nlm.nih.gov/pmc/articles/PMC3833266/.
- “Intermittent Fasting: What Is It, and How Does It Work?” Johns Hopkins Medicine, The Johns Hopkins University, www.hopkinsmedicine.org/health/wellness-and-prevention/intermittent-fasting-what-is-it-and-how-does-it-work.
- Antunes, Fernanda, et al. “Autophagy and Intermittent Fasting: the Connection for Cancer Therapy?” Clinics (Sao Paulo, Brazil), Hospital Das Clínicas Da Faculdade De Medicina Da Universidade De São Paulo, 10 Dec. 2018, www.ncbi.nlm.nih.gov/pmc/articles/PMC6257056/.
- Wilhelmi de Toledo, Françoise, et al. “Safety, Health Improvement and Well-Being during a 4 to 21-Day Fasting Period in an Observational Study Including 1422 Subjects.” PloS One, Public Library of Science, 2 Jan. 2019, www.ncbi.nlm.nih.gov/pmc/articles/PMC6314618/.