Intermittent fasting: risks and benefits
Fasting and intermittent fasting have gained popularity as potential methods to improve health and promote weight loss. They also carry religious or spiritual symbolism dating back to ancient times. Fasting cures are nothing new! However, their effectiveness and risks continue to spark debates among health professionals and researchers.
Fasting is defined as abstaining from food for a set period. This can range from several hours to several days, or even weeks in some cases. Intermittent fasting, on the other hand, involves cycling between fasting and eating periods, alternating between fasting windows and feeding windows. Common methods include the 16/8 fast (16 hours fasting, 8 hours eating), alternate-day fasting, and the 5:2 method (5 days normal eating, 2 days restricted calories).
The Claimed Benefits
Proponents of intermittent fasting highlight several potential health advantages. Weight loss is frequently cited, as intermittent fasting effectively reduces calorie intake—no miracle here: if you eat less or nothing, you lose weight. Additionally, some studies show that intermittent fasting may improve insulin sensitivity, regulate blood sugar, and lower blood lipid levels. That in turn would help reducing the risk of metabolic diseases such as type 2 diabetes and cardiovascular disease.
Another theory is that intermittent fasting promotes autophagy, a cellular “cleaning and regeneration” process that could help prevent premature aging. It is also often linked to reduced inflammation, with positive effects on preventing chronic inflammatory diseases.
But What Really Helps?
Despite studies showing these effects, fasting—regardless of the method—reduces food intake overall. This consequently cuts out processed foods and poorly tolerated items that may be the true culprits behind symptoms. When someone fasting sees certain inflammatory symptoms disappear (e.g., joint pain, respiratory issues, or skin problems), it might simply be because they have a an intolerance or an allergy causing inflammation. Is the solution really to stop eating? In most cases, the better approach is to identify potential allergies or intolerances. This allows improvement in the condition without drastic dietary restrictions.
The Risks
However, there are real concerns and risks associated with fasting. Prolonged fasting can lead to deficiencies in essential nutrients such as vitamins, minerals, and essential fatty acids. It can also cause blood sugar drops, which is problematic for diabetics or other conditions requiring close glucose monitoring.
Avoiding food may disrupt metabolism and lead to loss of lean muscle mass rather than just body fat. In the long term, this can have negative health consequences. Additionally, intermittent fasting can foster an unhealthy relationship with food, especially in those with a history of eating disorders.
In the end, a healthy, balanced diet combined with healthy lifestyle habits remains the simplest and most enjoyable way to maintain good long-term health.
References:
- Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis of randomised clinical trials (2025). The BMJ. DOI: 10.1136/bmj-2024-082007.
- Supports: Intermittent fasting provides similar weight loss and cardiometabolic benefits (e.g., lipids, blood pressure) to continuous energy restriction; no superior long-term effects; highlights calorie reduction as the main driver.
- Intermittent fasting and health outcomes: an umbrella review of systematic reviews and meta-analyses of randomised controlled trials (2024). eClinicalMedicine. DOI: 10.1016/j.eclinm.2024.102698
- Supports: Benefits in overweight/obese adults for fat mass reduction, insulin, lipids (LDL-C, TC, TG), but mixed on blood pressure; high-certainty evidence for some improvements, but not universally superior to other diets; notes potential increases in fat-free mass in some cases.
- Effects of intermittent fasting combined with resistance training on body composition: a systematic review and meta-analysis (2021, foundational; still cited in recent works). Physiology & Behavior. DOI: 10.1016/j.physbeh.2021.113453.
- Supports: When combined with resistance training, intermittent fasting reduces body/fat mass while generally preserving lean mass; without training, lean mass loss is more likely—aligns with the article’s muscle loss concern.
- Intermittent fasting: consider the risks of disordered eating for your patient (2023 commentary/review). PMC/NCBI.
- Supports: Links intermittent fasting to disordered eating risks, especially in those with history; restrictive patterns can mimic or trigger unhealthy food relationships—backs the article’s warning on psychological risks.
- The Beneficial and Adverse Effects of Autophagic Response to Caloric Restriction and Fasting (2023). PMC/NCBI.
