Intermittent Fasting for Beginners: Methods, Evidence and How to Start Safely

Intermittent fasting means limiting when you eat rather than, or as well as, what you eat. Popular methods include 16:8 time-restricted eating, the 5:2 diet and alternate-day fasting. Research shows it can help people lose weight, but large reviews in 2025 and 2026 found it generally works about as well as ordinary calorie reduction, not dramatically better. It is not suitable for everyone, including people who are pregnant, under 18, have a history of eating disorders or take certain diabetes medicines. This beginner’s guide explains how the main methods work, what the evidence says and how to start safely.

What Is Intermittent Fasting?

Intermittent fasting (IF) is an eating pattern that cycles between periods of eating and periods of not eating, or eating very little. Unlike most diets, it doesn’t specify particular foods. The idea is that by narrowing your eating time, you will naturally eat less overall, and that longer gaps without food may encourage the body to use stored fat for energy.

What Are the Main Types of Intermittent Fasting?

• 16:8 time-restricted eating: you eat within an eight-hour window each day, such as 10am to 6pm or noon to 8pm, and fast for the remaining 16 hours. Many beginners start with 12:12 or 14:10.
• 5:2 diet: you eat normally five days a week and cut to about 500–600 calories on two non-consecutive days.
• Alternate-day fasting: you alternate normal eating days with fasting or very low-calorie days.
• Eat-stop-eat: one or two 24-hour fasts a week, for example from dinner to dinner. This is harder and is generally not recommended for beginners.

During fasting periods, water, black coffee and plain tea are usually allowed. Diet drinks and supplements are debated, and the rules depend on the plan you follow.

Does Intermittent Fasting Work for Weight Loss?

Yes, but probably not because of anything special about fasting. Two large recent reviews give the clearest picture so far:

• BMJ, 2025: a network meta-analysis of 99 randomised controlled trials involving 6,582 adults found that intermittent fasting and continuous calorie restriction both led to weight loss compared with no diet. Alternate-day fasting showed a modest extra benefit, about 1.3 kg more than continuous calorie restriction, but most trials lasted under 24 weeks, so long-term effects are less certain.
• Cochrane, 2026: a review of 22 trials with 1,995 adults with overweight or obesity found that intermittent fasting probably makes little to no difference in weight loss compared with standard dietary advice or calorie restriction.

The practical message is that intermittent fasting is one way to eat less, not a shortcut. If an eating window helps you snack less in the evening, it may work well for you. If it leaves you ravenous and overeating later, a different approach may suit you better.

What Other Health Effects Does It Have?

Some studies have found improvements in blood sugar, insulin sensitivity, blood pressure and cholesterol with intermittent fasting, but these changes mostly track the amount of weight lost. Animal research on cell repair and longevity has attracted a lot of attention, but it has not been confirmed in human trials.

There are also open questions. A 2024 study presented at an American Heart Association conference, based on survey data from about 20,000 US adults, found that people who reported eating within less than eight hours a day had a 91% higher risk of death from cardiovascular disease over a median of eight years. The study was observational, relied on two days of self-reported eating, was presented as an abstract rather than a full peer-reviewed paper and cannot show cause and effect. Experts have urged caution in interpreting it, but it is a reminder that long-term evidence is still limited.

Who Should Not Try Intermittent Fasting?

The Mayo Clinic, Australia’s healthdirect and other health bodies advise that fasting is not suitable, or needs medical supervision, for:

• People who are pregnant or breastfeeding.
• Children and teenagers.
• Anyone with a current or past eating disorder.
• People with type 1 diabetes, or type 2 diabetes treated with insulin or sulfonylureas, because of the risk of low blood sugar.
• People who are underweight or frail, or older adults at risk of malnutrition.
• People who take medicines that need to be taken with food.

If you have a long-term health condition, speak to your doctor before changing how you eat.

How Do You Start Intermittent Fasting?

• Pick the simplest method. For most beginners, that is a 12-hour overnight fast, such as 7pm to 7am, which many people already almost do.
• Extend gradually. Move to 14:10 and then 16:8 over a few weeks if you feel well.
• Choose a realistic window. Fit it around your work, family meals and exercise. An earlier window, such as 9am to 5pm, is harder socially but may suit body clocks better.
• Plan your meals. Base them on vegetables, fruit, whole grains, beans, fish, eggs, lean meat and dairy or alternatives.
• Eat enough protein to stay full and protect muscle. Our guide to how much protein you need per day explains the targets.
• Stay hydrated with water, tea or black coffee during the fast.
• Track how you feel, not just your weight. Energy, sleep, mood and hunger all matter.

What Should You Eat When You Break a Fast?

There are no special “fast-breaking” foods. A balanced meal with protein, fibre and healthy fats is ideal, such as eggs and wholegrain toast, Greek yoghurt with fruit and nuts, or a salad with chicken, beans or tofu. Avoid using the eating window as permission to eat large amounts of ultra-processed food. The quality of what you eat still matters for long-term health.

Make sure your overall diet still covers key nutrients. Shorter eating windows can mean fewer meals and less variety, so pay attention to fibre, calcium and vitamin D. Our guide to how much vitamin D you need per day explains the recommendations.

What Are the Common Side Effects?

In the first week or two, many people notice hunger, irritability, headaches, tiredness or trouble concentrating, especially in the late afternoon. These often ease as the body adjusts. Drinking enough water, eating sufficient protein and fibre in your eating window and starting with a shorter fast can help.

Stop and seek advice if you feel dizzy or faint, notice palpitations, become preoccupied with food, or find yourself binge eating after fasts.

Can You Exercise While Fasting?

Yes. Many people walk, run or lift weights during a fast without problems. Some prefer to schedule harder sessions shortly before or within their eating window, so they can eat afterwards. If you train hard or for long periods, a fasting schedule that leaves you underfuelled may reduce performance and recovery. If you’re starting a running habit, our guide to whether running is bad for your knees explains how to build up safely.

What Are the Key Takeaways?

• Intermittent fasting limits when you eat; popular methods are 16:8, 5:2 and alternate-day fasting.
• Major 2025 and 2026 reviews found it works for weight loss, but generally about as well as ordinary calorie reduction.
• It is not suitable for everyone, including people who are pregnant, under 18, have had an eating disorder or take some diabetes medicines.
• Start with a 12-hour overnight fast and build up slowly.
• Food quality still matters: build meals around protein, fibre, fruit, vegetables and whole grains.

This article is general information and not medical advice. Speak to a doctor or registered dietitian before making significant changes to your diet, especially if you have a health condition or take regular medicines.

Featured image: Hard boiled egg on breakfast table, by Marc-Lautenbacher / Wikimedia Commons, CC BY-SA 4.0. Cropped, colour-graded and combined with MediaPavilion branding.

Sources

• The BMJ — Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis (2025).
• Cochrane Database of Systematic Reviews — Intermittent fasting for adults with overweight or obesity (2026).
• American Heart Association Newsroom — 8-hour time-restricted eating linked to a 91% higher risk of cardiovascular death (18 March 2024).
• Mayo Clinic — Intermittent fasting: what are the benefits? (accessed 25 October 2026).
• healthdirect Australia — Intermittent fasting (accessed 25 October 2026).
• NHS — The Eatwell Guide (accessed 25 October 2026).