Intermittent fasting cycles between periods of eating and fasting to improve metabolic health and aid weight management — but it is not suitable for everyone.
Intermittent fasting (IF) refers to eating patterns that cycle between periods of fasting and eating. Unlike traditional diets, IF does not specify which foods to eat but focuses on when to eat. Several methods have become popular: the 16:8 method (16 hours fasting, 8-hour eating window), the 5:2 diet (normal eating 5 days, very restricted calories on 2 non-consecutive days), and alternate day fasting.
During fasting periods, insulin levels fall, triggering fat breakdown for energy. After 12+ hours of fasting, the body enters mild ketosis and begins producing ketone bodies from stored fat. This metabolic switch is thought to underlie many of IF's benefits.
Evidence-based benefits include: moderate weight loss (comparable to continuous caloric restriction), improvements in insulin sensitivity and blood glucose control, reduction in inflammatory markers, lower LDL cholesterol and triglycerides, and potential cognitive benefits through autophagy (cellular cleaning process activated during fasting).
IF is not suitable for everyone. It is contraindicated in pregnancy, breastfeeding, people with a history of eating disorders, children, and those with type 1 diabetes. People with type 2 diabetes can potentially benefit from IF but require close medical supervision, especially if on insulin or sulphonylureas which can cause hypoglycaemia during fasting.
Key Points
- Most studied methods: 16:8 (16 hours fasting daily) and 5:2 (2 restricted days per week)
- Works primarily by reducing overall calorie intake and improving insulin sensitivity
- Comparable weight loss results to continuous caloric restriction in most studies
- Most protocols allow water, black coffee, and tea during fasting periods
- Not recommended in pregnancy, breastfeeding, eating disorder history, or children
- Consult a doctor before starting if you have diabetes or take regular medication
When to See a Doctor
- If you have type 2 diabetes and want to try IF — medication adjustments may be needed
- If you experience persistent dizziness, headaches, or extreme fatigue during fasting
- If you have a history of eating disorders
- If you are taking medications that must be taken with food
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This article is published by DoctorsInKorea.com for educational and informational purposes only. It does not replace a professional clinical evaluation by a licensed healthcare provider. For accurate medical diagnosis and personalised treatment paths, please book an appointment with a licensed KMA physician. For immediate life-threatening medical emergencies in Korea, please call 119.
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Last reviewed: April 1, 2026