Intermittent fasting (IF) is an eating pattern that alternates between periods of fasting and eating. Unlike conventional diets that focus on what to eat, IF focuses on when to eat. It has become one of the most popular health and weight loss approaches in the world — and the science behind it is solid.
How does intermittent fasting work?
When you eat, your body spends several hours processing and absorbing the food. During this time, insulin is elevated and your body primarily burns glucose for fuel. After about 12 hours without eating, insulin levels drop low enough for your body to begin accessing stored fat for energy. This metabolic switch from glucose-burning to fat-burning is the core mechanism behind IF's weight loss benefits.
The main IF methods
16:8 (Leangains Protocol) — most popular
Fast for 16 hours, eat within an 8-hour window. Most people skip breakfast and eat between 12pm–8pm or 1pm–9pm. This is the easiest IF method to maintain long-term because it simply extends the overnight fast.
5:2 Diet
Eat normally for 5 days per week. Restrict calories to 500–600 kcal on 2 non-consecutive days. The fasting days are not complete fasts — you eat a very small amount. This method suits people who prefer not to fast daily.
OMAD (One Meal a Day)
Eat all daily calories in a single meal within a 1-hour window. Very aggressive — not recommended for beginners. Can make it difficult to consume adequate protein and nutrients in one sitting.
Eat Stop Eat
Fast for 24 hours, once or twice per week. Eat normally the other days. The 24-hour fast runs from dinner to dinner (e.g. eat dinner Monday, fast until dinner Tuesday).
Benefits of intermittent fasting
Weight and fat loss
The primary mechanism is calorie reduction — most people naturally eat fewer calories when restricting their eating window. Research suggests IF produces comparable weight loss to continuous calorie restriction, with some evidence for greater fat loss specifically.
Improved insulin sensitivity
Regular fasting periods lower fasting insulin levels and improve insulin sensitivity, which may reduce risk of type 2 diabetes. Studies show reductions in fasting blood sugar of 3–6% and fasting insulin of 20–31%.
Cellular repair (autophagy)
Fasting triggers autophagy — a cellular clean-up process where cells break down and remove damaged proteins and components. This process is linked to longevity and reduced cancer risk in animal studies, though human evidence is still emerging.
Simplicity
Many people find IF simpler than calorie counting because it replaces complex meal planning with one rule: only eat during your eating window.
Who should avoid intermittent fasting?
- Pregnant or breastfeeding women
- People with a history of eating disorders
- People with type 1 diabetes or on insulin medication
- Children and teenagers
- People who are underweight
Always consult a doctor before starting IF if you have any medical condition.
How to start intermittent fasting
The easiest approach for beginners: start with 12:12 (12 hours fasting, 12 hours eating). Gradually extend the fasting window by 30 minutes each week until you reach 16:8. During the eating window, focus on nutrient-dense foods and adequate protein (1.6–2.2g/kg) to preserve muscle mass.
Common IF mistakes
- Overeating in the eating window — IF only works if you naturally consume fewer calories. Deliberately eating more to "compensate" eliminates the benefit.
- Not eating enough protein — A compressed eating window makes it harder to meet protein targets. Prioritise protein at every meal.
- Breaking the fast with high-sugar foods — After a fast, insulin sensitivity is high. Prioritise protein and vegetables over simple carbohydrates.
- Expecting immediate results — The body takes 2–4 weeks to adapt to a new eating schedule. Initial side effects (hunger, headaches, irritability) are normal and typically resolve.