"The Myth of 'Fasting Works for Everyone'" — Inflammation and Metabolism Differentiate "People It Works For/People It Doesn't Work For": Is the "Switch" Harder to Activate in Obesity?

A 2025 study published in iScience demonstrated that responses to a 48-hour fast vary depending on body type. While all participants experienced increased fat burning, those in the obese group showed a slower rise in ketone bodies and weaker immune adaptation, specifically in the switch of T cells to fatty acid oxidation. Inflammatory signals such as inflammatory T cells (Th17) and IL-17 remained elevated in the obese group, suggesting a lower metabolic flexibility. A general audience article summarized that "fasting does not work the same for everyone," recommending that particularly obese individuals should start with shorter fasts (e.g., 16:8) under medical supervision and combine them with an anti-inflammatory diet. On social media, opinions were mixed, with comments like "easy to continue," "equivalent to calorie restriction," "protein is important," and "overemphasis on autophagy is inadvisable." In conclusion, fasting is not a universal solution, and personalization is key. It is important not to confuse the study's premise (48 hours, small scale) with everyday intermittent fasting (IF).