Intermittent fasting for weight loss

Intermittent fasting has become one of the most talked-about non-medicated approaches for weight loss. You might have heard friends talk about it, or seen claims online about improved health and easier weight loss. You might even be considering it yourself, but still feel uncertain about what it actually involves.

Put simply, the idea is that instead of focusing on what you eat, you switch the focus to when you eat [1,2]. But is intermittent fasting genuinely more effective than other dietary methods, or simply another way of creating a calorie deficit?

This article explores what intermittent fasting actually involves, including the most common ways of doing it, what the research says, and the potential pros and cons. By the end, you’ll know what to expect and whether it could be a good fit for you.

What is Intermittent Fasting?

The term intermittent fasting is sometimes used interchangeably. For some, it refers to time-restricted eating (daily eating windows such as 16:8). For others, it means patterns like the 5:2 diet or alternate-day fasting. Generally speaking, intermittent fasting describes any eating pattern that cycles between periods of fasting and periods of eating, but the details can vary.

In time-restricted eating, fasting periods usually mean consuming no calories at all [3]. Water, black coffee, and unsweetened tea are allowed because they don’t provide any calories so don’t break the fast [3]. By contrast, in approaches like the 5:2 diet or alternate-day fasting, “fasting days” are actually very low-calorie days [2,6].

All forms of intermittent fasting are designed to help reduce overall calorie intake. Weight loss is often most noticeable in the first few weeks [2], but the main driver of results is still creating a calorie deficit rather than the timing alone [4].

Popular Approaches to Intermittent Fasting for Weight Loss

The 5:2 diet.

The original design of intermittent fasting is often known as the 5:2 diet. You eat normally on five days of the week, and on two non-consecutive days you reduce intake to around 500–600 calories, roughly 25% of your daily needs [2].

Whilst this may work for some, it can be difficult to sustain as it often limits social flexibility and energy on fasting days. Sometimes unexpected plans come up, and no diet should be stopping you enjoying your life. Thankfully, there are other ways to structure fasting that may feel more flexible.

Time-Restricted Eating

Time-restricted eating applies fasting to each day. You fast for a set number of hours (including overnight) and eat within a shorter timeframe during the day. You might hear terms such as “eating window” and “fasting window”. Here are a few variations on time-restricted eating:

• 12:12 – Fast for 12 hours, eat within a 12-hour window (e.g. 8am–8pm).
• 14:10 – Fast for 14 hours, eat within 10 hours (e.g. 10am–8pm).
• 16:8 – Fast for 16 hours, eat within 8 hours (e.g. 12pm–8pm). One of the most common approaches, which most often just means skipping breakfast.
• 18:6 – A stricter pattern, fasting for 18 hours and eating in a 6-hour window.

People often report benefits like more energy, lighter digestion, and less bloating within a couple of weeks [5].

Starting with a 12:12 or 14:10 window can make the transition easier before moving to longer fasting periods [3]. Choosing a window depends on your lifestyle, social schedule, and preferences. What matters most is finding one that feels sustainable for you.

Alternate-Day Fasting

Another option is alternate-day fasting, which follows a similar calorie approach to 5:2 but on a different schedule. This approach alternates fasting days with normal eating days. On fasting days, the calorie allowance is the same as the 5:2 diet. This means around 500–600 calories, or roughly 25% of daily needs on fasting days [2,6]. On eating days, food intake is unrestricted.

The main difference is the frequency. Instead of just two fasting days per week, as in the 5:2, alternate-day fasting means fasting every other day. Because it involves more frequent low-calorie days, some people find it harder to maintain without guidance or support.

Side Effects of Intermittent Fasting for Weight Loss

Like any dietary change, intermittent fasting can take time to adjust to. Side effects may include headaches, tiredness, irritability, constipation, hunger, or brain fog [2,7,8]. These usually improve after the first couple of weeks.

Hunger on fasting days can be difficult to manage if you’re not sure how to make the most of your calories. Choosing low-calorie, nutrient-dense foods that are rich in protein, fibre, and healthy fats will help you stay satisfied [6,9]. With the right knowledge or support, this becomes much easier to get right.

And while intermittent fasting doesn’t dictate what you eat, choosing nutrient-dense meals is also important for maintaining energy and avoiding nutrient gaps [2,9].

Who Should Avoid Intermittent Fasting

Intermittent fasting is not recommended if you are [2,3,6,10]:

• Under 18.
• Pregnant, breastfeeding or trying to conceive.
• Living with or recovering from an eating disorder.
• Managing a condition where weight loss would be harmful.
• On medications or supplements that must be taken with food.

Shift workers and people with high energy needs (e.g. athletes) may also find fasting disruptive or impractical [2].

Practical Tips if You’re Considering Intermittent Fasting

To make fasting easier to stick with, consider these strategies [2,3,5,6]:

• Start gradually: Try a 12-hour overnight fast before moving to 14:10 or 16:8.
• Stay hydrated: Water, black coffee, and unsweetened tea do not break a fast.
• Plan workouts: Exercising near your eating window makes refuelling easier.
• Finish meals earlier: Eating earlier in the day may better align with your body’s natural rhythms.
• Choose quality foods: Focus on whole, nutrient-dense meals.
• Listen to your body: If you feel faint, nauseous, or unwell, break your fast and reconsider your approach.
• For women: Pay attention to hormonal symptoms or menstrual changes. If cycles become irregular or energy availability feels too low, fasting may not be the right choice.

Bottom line

Intermittent fasting for weight loss isn’t a magic bullet. Instead, it works because it helps some people reduce their calorie intake, not because the timing itself is uniquely powerful [4].

For some, it’s a simple, flexible way to reduce calories and may also bring early wins like improved energy, mood, or digestion [5]. On the other hand, it can feel restrictive or unsustainable.

That’s why any dietary approach should be personalised to you and your lifestyle. So, if you feel like you’ve tried everything and nothing seems to stick, you might find this blog, “I’ve tried them all”, reassuring. It’s a reminder that you don’t have to keep forcing yourself into approaches that don’t fit.

Ultimately, if you’re wondering whether intermittent fasting is right for you, please book in to speak with me. Together we can explore whether fasting could be a good fit, or find another approach that supports your weight loss in a healthy, sustainable way.

For more information on the above or for ways on how to work with me get in touch, I’d love to hear from you.

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3. ZOE. How to fast: your guide to fasting safely. [Internet]. 2023 [cited 19 Sep 2025]. Available from: https://zoe.com/learn/how-to-fast
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5. ZOE. What schedule can you follow for intermittent fasting? [Internet]. 2023 [cited 19 Sep 2025]. Available from: https://zoe.com/learn/intermittent-fasting-schedule
6. ZOE. Intermittent fasting for women: what women should know before trying intermittent fasting. [Internet]. 2023 [cited 19 Sep 2025]. Available from: https://zoe.com/learn/intermittent-fasting-for-women
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10. Simple, 2021. Can you fast while taking medications? Accessed 16th April 2023. Online, available at: https://simple.life/blog/intermittent-fasting-and-medication/