Intermittent Fasting for Weight Loss: Does It Really Work?

Intermittent fasting for weight loss is one of the most popular approaches I get asked about. Some people swear by it, others find it miserable. The honest answer is that it can work well, but not for the reasons people often think, and it is not right for everyone.

In this guide I explain the two most common methods, 16:8 and 5:2, why the results still come down to calories, who fasting tends to suit, and who should avoid it or speak to their GP first.

What is intermittent fasting?

Intermittent fasting means organising your eating around set times, with planned periods of not eating. It does not tell you what to eat, only when. Water, black coffee and plain tea are usually fine during the fasting window.

The 16:8 method

You fast for 16 hours and eat within an 8 hour window each day. A common setup is eating between 12pm and 8pm, which mostly means skipping breakfast. Some people prefer a 10am to 6pm window so they do not eat late.

The 5:2 method

You eat normally on five days of the week and cut right back on two non-consecutive days, often to around 500-600 calories. For example, low-calorie Mondays and Thursdays, with normal, sensible eating the rest of the week.

Other versions

There are stricter options such as alternate-day fasting or 24-hour fasts. They are harder to sustain and I rarely recommend them for busy professionals who are also training.

Does intermittent fasting for weight loss actually work?

Yes, it can, but mainly because it helps people eat less overall. If you shrink your eating window from 14 hours to 8, you usually cut out some snacking, late-night grazing or a biscuit-heavy breakfast. Fewer eating occasions often means fewer calories.

What fasting does not do is cancel out a calorie surplus. If you eat 3,000 calories in an 8 hour window and your body needs 2,300, you will still gain weight. Fat loss depends on a calorie deficit, whichever eating pattern you use to get there. If the idea of energy balance is new, my guide to calories explained is a good primer.

Generally, when total calories and protein are the same, fasting and a regular eating pattern tend to give similar results. The best method is the one you can stick to.

Who intermittent fasting tends to suit

• People who are not hungry in the morning and find breakfast a chore.
• Busy professionals who like fewer food decisions during a packed workday.
• Evening snackers who benefit from a firm "kitchen closed" time.
• People who prefer bigger, more satisfying meals over several small ones.

If that sounds like you, 16:8 is usually the easier starting point. My post on fat loss for busy professionals has more ideas for fitting eating around long days.

Pros and cons of intermittent fasting

Pros

• Simple rules that are easy to remember.
• Can reduce mindless snacking and late-night eating.
• No foods are banned, so it fits social life fairly well.
• Some people find it frees up time and mental energy.

Cons

• Hunger, irritability or headaches, especially in the first couple of weeks.
• Easy to overeat when the window opens, which cancels the benefit.
• Harder to hit your protein target in fewer meals, which matters if you want to keep muscle.
• Training on an empty stomach feels poor for some people.
• Can clash with family meals or work dinners.

How to do 16:8 well if you train

If you lift weights and want to lose fat without losing muscle, a few rules make fasting much more effective:

1. Get enough protein. Aim for 2-3 protein-rich meals in your window, each with a good portion of chicken, fish, eggs, Greek yoghurt, beans or tofu. See my guide to protein for beginners.
2. Plan your first meal. Break the fast with a proper meal, not whatever is in the office kitchen.
3. Train near your window if you can. Many people feel better training just before or after their first meal. My article on nutrient timing explains what matters and what does not.
4. Keep the window consistent. Same times most days makes hunger more predictable.
5. Still track calories, at least at first. A week or two of tracking shows whether your window is creating a deficit.

Want help with this? I do not push one diet on everyone. Some of my clients use 16:8, many do not, and both groups lose fat when the calories, protein and training are right. Book a free consultation and we will work out which approach fits your schedule. You can also read about my weight loss personal training.

Who should avoid intermittent fasting or check with a GP

Fasting is not safe or sensible for everyone. Speak to your GP before trying it, or avoid it, if you:

• Are pregnant, trying to get pregnant or breastfeeding.
• Have diabetes, particularly if you take insulin or other medication that lowers blood sugar.
• Have a history of an eating disorder or a difficult relationship with food.
• Take medication that needs to be taken with food.
• Have low blood pressure, are underweight, or have any other medical condition.
• Are under 18 or older and frail.

If you feel dizzy, faint or unwell while fasting, stop and seek medical advice. If fasting is not for you, working with a personal trainer in Archway on a structured plan can help you lose weight with regular meals instead.

Frequently asked questions

How much weight can you lose with intermittent fasting?

It depends on the calorie deficit you create, not the fasting itself. If 16:8 or 5:2 helps you eat around 500 calories a day less than you need, a loss of roughly 0.5kg a week is realistic for many people. Early weeks often look faster because of water loss, then progress settles.

Is 16:8 or 5:2 better for weight loss?

Neither is clearly better. Both work if they lead to fewer calories overall. 16:8 suits people who dislike breakfast and want a daily routine. 5:2 suits people who would rather eat normally most days and accept two harder days. Pick the one you can follow for months, not just a fortnight.

Can I drink coffee while intermittent fasting?

Black coffee, plain tea and water are generally fine during a fast and can help with hunger. Adding milk, sugar or syrups adds calories, so a splash of milk is a small compromise many people accept. Watch how much caffeine you have, because a lot on an empty stomach can affect sleep and digestion.

Can you build muscle while intermittent fasting?

You can maintain and even build some muscle while fasting, as long as you train with weights regularly, eat enough protein in your window and are not in too big a deficit. It can be harder to fit in enough protein, so plan two or three protein-rich meals rather than relying on snacks.

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