Intermittent Fasting Planner

What is intermittent fasting?

Intermittent fasting (IF) is an eating pattern that cycles between periods of fasting and eating. Unlike a traditional diet, IF doesn't prescribe which foods to eat — it specifies when you eat them. The most popular protocol is 16:8: 16 hours of fasting followed by an 8-hour eating window.

IF has become one of the most researched dietary approaches of the past decade. A 2022 review in the New England Journal of Medicine found that time-restricted eating can improve metabolic markers including insulin sensitivity, blood pressure, and inflammatory markers — though most benefits are mediated through calorie reduction rather than fasting itself.

How to choose the right fasting protocol

16:8 — The best starting point

The 16:8 protocol is the most widely practised form of IF. It requires only skipping breakfast (or eating an early dinner), fits into most daily routines, and has a substantial body of research supporting its safety. For most people, eating between noon and 8pm is the simplest implementation.

18:6 — A meaningful step up

Extending the fast to 18 hours with a 6-hour eating window increases the potential metabolic benefits but requires more planning. Best suited for people who have already adapted to 16:8. A common implementation is eating between 1pm and 7pm.

20:4 (Warrior Diet) — Advanced fasting

The 20:4 protocol involves a 20-hour fast and a 4-hour eating window. This requires careful attention to nutritional completeness — getting adequate protein, vitamins, and minerals within a very short window. Not recommended for beginners.

OMAD — One meal a day

OMAD involves a single eating window of approximately one hour. Some studies suggest it may reduce lean muscle mass more than less extreme protocols. Not recommended without medical supervision.

5:2 — The alternate-day approach

Rather than restricting the hours you eat each day, 5:2 involves eating normally five days per week and consuming only 500–600 calories on two non-consecutive days. Studies show comparable weight loss to daily calorie restriction in overweight adults.

What actually happens during a fast?

0–4 hours: Fed state

After eating, blood glucose and insulin are elevated. Your body uses glucose as its primary fuel. Digestion is active — nutrients from the meal are being absorbed and distributed.

4–8 hours: Post-absorptive state

Digestion completes. Insulin begins to fall. Your body draws on liver glycogen (stored glucose) for energy. Fat oxidation begins to increase slightly as insulin drops.

8–12 hours: Early fasting

Liver glycogen stores deplete. Fat oxidation increases significantly. Growth hormone secretion rises. Cellular repair processes (autophagy) begin to activate at low levels.

12–16 hours: Extended fasting

Ketone production begins as the liver converts fatty acids. Autophagy becomes more active. Insulin reaches its lowest point of the day. Noradrenaline rises, increasing alertness and metabolic rate modestly.

Beyond 16 hours: Prolonged fasting

Ketosis deepens. Autophagy increases further. Beyond 24 hours, the changes become more pronounced — but also carry more risk of muscle loss without adequate protein intake. Protocols beyond 20:4 or OMAD are not recommended without medical guidance.

Common mistakes beginners make

Breaking the fast with poor food choices

IF is not a free pass to eat anything within your window. Breaking a fast with highly processed, calorie-dense foods undermines the benefits of the fasting period. Prioritise protein, vegetables, and whole foods when you break your fast.

Not drinking enough water

Many people mistake thirst for hunger during the fasting window. Aim to drink at least 2–3 litres of water throughout the day. This also helps manage hunger and supports the cellular processes activated during fasting.

Choosing too aggressive a protocol too soon

Starting with OMAD or 20:4 when you have no fasting experience is a common cause of failure. Begin with 16:8 and allow 2–4 weeks for your body to adapt before progressing.

Expecting immediate results

Meaningful changes from IF typically take 6–12 weeks to become apparent. The first 2 weeks are often accompanied by hunger and irritability as your body adapts to a new eating pattern.

What can you consume during a fast?

Water, black coffee, and plain tea are generally considered acceptable during a fast as they contain no (or negligible) calories and don't significantly raise insulin levels. Adding milk, sugar, or cream would technically break the fast.

Is intermittent fasting right for you?

IF is not appropriate for everyone. Pregnant or breastfeeding women, people with a history of eating disorders, those with type 1 diabetes, and children should avoid fasting without medical supervision. Always consult a healthcare professional before starting any fasting protocol.

People who tend to do well with IF typically prefer structured eating, skip meals naturally, or find calorie counting difficult to maintain. People who struggle often have jobs requiring high-intensity physical activity early in the morning, or find that restricted eating windows increase food preoccupation.

Intermittent fasting and exercise

Training while fasted is viable for most people at moderate intensities. Low-to-moderate intensity exercise (walking, Zone 2 cardio) in a fasted state can increase fat oxidation. High-intensity training — intervals, heavy strength work — typically performs better with some carbohydrate available.

If you train in the morning, consider placing your eating window around your training — for example, eating from noon to 8pm if you train in the late morning. Breaking the fast with protein and carbohydrates immediately after training supports recovery and muscle protein synthesis.

For strength training specifically: research suggests IF does not impair muscle gain when total protein intake is adequate (1.6–2.2g/kg). The timing of protein within the eating window matters less than hitting the daily total.

Intermittent fasting for women

Women may respond differently to intermittent fasting than men, particularly at more aggressive protocols. Some women report disrupted menstrual cycles, increased hunger, and mood changes with strict IF — effects thought to be related to hypothalamic sensitivity to caloric restriction. These responses are more common with 20:4 and OMAD than with 16:8.

For women, starting with a shorter fast (14:10 or 16:8) and monitoring energy levels and cycle regularity is recommended. If IF is disrupting sleep, mood, or menstrual function, stepping back to a more moderate approach or abandoning IF in favour of simple calorie awareness is entirely reasonable.

Women over 40 approaching perimenopause or menopause may find IF particularly useful for managing appetite and metabolic changes — but should pay particular attention to protein intake, as oestrogen decline accelerates muscle loss.