Intermittent fasting: the complete guide to starting and progressing

Intermittent fasting isn't a diet in the traditional sense — it's an eating pattern. You don't change what you eat, but when you eat. Protocols range from 16:8 (beginner-friendly) to 24-48 hour fasts (advanced). This guide explains the science, the different protocols, and especially the often-ignored contraindications.

Steps

1

Choose your starting protocol

16:8 (16 hours fasting, 8 hours eating) is the most accessible: skip breakfast and eat from noon to 8 PM. 14:10 is even gentler for beginners. 5:2 (5 normal days, 2 days at 500-600 kcal) works for those who prefer occasional restriction over daily limits. Eat-stop-eat (24h fast 1-2 times a week) and OMAD (One Meal A Day) are for experienced practitioners only.

2

Start gradually

Don't jump from three meals + snacks to a 24-hour fast overnight. Start by delaying your breakfast by one hour each day for a week. Then by two hours. Within 10-14 days, you'll naturally reach a 14:10 or 16:8 pattern without suffering. This gradual approach minimizes hunger, irritability, and headaches.

3

Stay well-hydrated

During the fasting window, you can (and must) drink: water, sparkling water, black tea, green tea, and black coffee without sugar or milk. Hydration is crucial because hunger is often confused with thirst. Black coffee is a fasting ally: it suppresses appetite and slightly stimulates fat oxidation. Avoid sugary drinks, even zero-calorie ones, which can stimulate insulin.

4

Break your fast intelligently

After 16+ hours of fasting, avoid jumping straight into a heavy meal rich in simple sugars. Start with a moderate meal high in protein and vegetables. Eggs, fish, a chicken salad, or a quinoa-veggie bowl are excellent first meals. Gradually increase food volume throughout your window. A first meal that is too large often causes bloating and drowsiness.

5

Adapt your physical exercise

Fasted training is possible and even beneficial for fat oxidation in endurance sports. For weightlifting, the ideal is to train near the end of your fasting window and eat immediately after. If you train in the morning while fasting, high-intensity performance might dip — in that case, schedule your intensity sessions during your eating window and keep morning cardio light.

6

Listen to your body

Intermittent fasting is not a penance. If you feel dizzy, shaky, unable to focus, or persistently irritable, break the fast. If these symptoms keep happening, the protocol is too aggressive for you — shorten your fasting window or try a different method. Flexibility is a strength, not a weakness.

Popular Protocols Explained

16:8 (or "Leangains") is the most studied and practiced: skipping breakfast allows you to concentrate 2-3 meals between noon and 8 PM. 5:2 (popularized by Dr. Michael Mosley) alternates 5 normal days with 2 non-consecutive days at 500-600 kcal — great for people who hate daily restrictions. Eat-stop-eat involves a 24-hour fast once or twice a week (e.g., dinner-to-dinner). OMAD (One Meal A Day) concentrates all food into a single meal — effective for some, but carries a risk of under-eating for others. Every protocol has benefits; the best one is the one you can stick to long-term.

What happens in your body during fasting

During the first 4-8 hours, your body draws from hepatic glycogen (liver glucose stores). Around 12-16 hours, glycogen is depleted and fat oxidation significantly increases. Growth hormone rises (up to 5x after a 24-hour fast), protecting muscle mass during fat mobilization. Autophagy — the "cellular cleanup" process where cells recycle damaged components — kicks in significantly after 16-24 hours. Insulin drops to its minimum, promoting long-term insulin sensitivity.

Who should NOT fast

Intermittent fasting is discouraged for pregnant or breastfeeding women, people with a history of eating disorders (anorexia, bulimia), Type 1 diabetics, growing children and adolescents, and people on medication that must be taken with food at fixed times. Women of childbearing age should be cautious: some studies suggest that prolonged fasting can disrupt the menstrual cycle and the female hormonal axis. A 14:10 protocol is generally better tolerated than 16:8 by women.

FoodCraft Tip

FoodCraft planning respects your eating window

FoodCraft's AI can generate meal plans concentrated within your eating window. Choose a 16:8 protocol, and your meals will be scheduled for 2-3 sittings between noon and 8 PM, with calories and macros properly distributed to maximize satiety and performance.

Fasting-adapted calorie calculator

FoodCraft's free calculator determines your caloric needs regardless of your eating window. Your daily caloric total remains the same whether you eat 3 meals or 2 — what changes is the distribution. The tool helps you reach your goals without under-eating.

Frequently asked questions

Does intermittent fasting burn more fat than traditional calorie restriction?
When calories are equal, weight loss is similar. The advantage of intermittent fasting is practical: many people find it easier to not eat at all for 16 hours than to eat small amounts at every meal. Adherence is often better, and adherence determines long-term results.
Can I drink coffee with milk during my fast?
A splash of milk (10-30 ml) is a debated topic. Technically, it adds 5-15 kcal and slightly stimulates insulin. In practice, this impact is negligible for weight loss. If coffee with milk helps you stick to the fast, it's a very acceptable compromise. Coffee with sugar, however, clearly breaks the fast.
Does fasting cause muscle loss?
No, as long as you consume enough protein (minimum 1.6g/kg) and do resistance training. The increase in growth hormone during fasting is specifically a muscle-protection mechanism. Studies on 16:8 in trained subjects show fat loss without significant loss of muscle mass.
How long before I see results?
Effects on energy and mental clarity are often felt in the first week. Visible weight loss generally takes 2-4 weeks. Deep metabolic benefits (insulin sensitivity, regular autophagy) are built over months of consistent practice.
Can you fast every day indefinitely?
Daily 16:8 is practiced by many people for years without issues. For more aggressive protocols (5:2, eat-stop-eat, OMAD), "break" periods where you return to normal eating for a few weeks are recommended to avoid adrenal fatigue and maintain a healthy relationship with food.

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