Here is the headline most intermittent fasting content leaves out: in the best head-to-head trials, eating within a time window leads to about the same weight loss as simply eating a bit less, spread across the day. The real intermittent fasting benefits are practical rather than magical. For some people, a clear "kitchen closed" rule makes eating less easier. For others, it backfires, and for a few groups it is not safe without medical guidance.

What is intermittent fasting, exactly?

"Intermittent fasting" is an umbrella term for eating patterns that cycle between eating and not eating. The main types are:

• Time-restricted eating (TRE): eating within a daily window, such as 16:8 (16 hours fasting, 8 hours eating) or a gentler 14:10.
• 5:2: eating normally five days a week and around 500 to 600 calories on two non-consecutive days.
• Alternate-day fasting: alternating normal days with very low-calorie or zero-calorie days.

Many readers here already know fasting in a very different form: Ramadan, where Muslims abstain from food and water from dawn to sunset. That is a religious practice with its own rhythm and meaning, and it differs from most IF protocols, which allow water, black coffee and plain tea during the fast. Research on Ramadan fasting is a separate field, so do not assume findings transfer directly in either direction.

What are the real intermittent fasting benefits?

A widely cited 2019 review in the New England Journal of Medicine by Rafael de Cabo and Mark Mattson described how fasting periods trigger a "metabolic switch", where the body shifts from using glucose to burning fat and producing ketones. In animal studies this switch is linked to improved insulin sensitivity, lower inflammation and longer lifespan.

The human evidence is more modest. Here is an honest summary:

What do the big trials say?

Three studies are worth knowing because they get quoted, and misquoted, a lot.

The 2022 NEJM trial (Liu and colleagues). In China, 139 adults with obesity were assigned to calorie restriction alone or calorie restriction eaten between 8am and 4pm, for 12 months. Both groups lost weight, around 6 to 8 kg on average, and the difference between them was not statistically significant. The takeaway: the calories did the work, not the clock.

The 2020 TREAT trial in JAMA Internal Medicine (Lowe and colleagues). Adults assigned to a 16:8 window, without other diet advice, lost only slightly more weight than a control group over 12 weeks, and the difference was not significant. There were also signs that some of the weight lost was lean mass, which is a reason to keep protein and strength training up if you fast.

The 2024 American Heart Association conference abstract. Headlines claimed that eating within 8 hours was linked to a much higher risk of cardiovascular death. This was an observational analysis based on a couple of days of dietary recall, presented as an abstract rather than a peer-reviewed paper, and it could not show cause and effect. It is a reason for curiosity, not panic.

Who does intermittent fasting tend to help?

• People who snack late at night. A firm cut-off, say 8pm, removes the supper run to the mamak and the post-dinner biscuits.
• People who genuinely are not hungry in the morning. If you already skip breakfast comfortably, formalising it may just make your routine easier.
• People who like simple rules. "Eat between 10am and 7pm" is easier for some than counting anything.
• Some people with prediabetes or excess weight, under medical guidance, where a structured approach helps them eat less.

Who should skip it or get advice first?

• Anyone with a current or past eating disorder. Rigid food rules can trigger restriction and bingeing cycles.
• Pregnant or breastfeeding women, who have higher and steadier nutrient needs.
• People taking insulin or sulfonylureas (such as gliclazide) for diabetes, because of the risk of low blood sugar. Medication often needs adjusting.
• Teenagers and children, who are still growing.
• People with low body weight, or older adults at risk of muscle loss.
• People who find it makes them irritable, dizzy, unable to focus or prone to overeating when the window opens. That is useful data, not a failure.

It can also clash with real life. Shift workers, parents feeding young children and anyone whose social life revolves around late dinners may find the window hard to hold. A rule you break four nights a week will mostly produce guilt.

How to try it sensibly

If you want to experiment, a gentle approach looks like this:

1. Start with 12 hours overnight, for example 8pm to 8am. Many people already do this.
2. Move to 14:10 if it feels easy after a couple of weeks. There is no strong evidence that 16:8 or longer is better for most people.
3. Favour an earlier window where possible, finishing dinner by around 7 or 8pm, which also tends to help sleep.
4. Break the fast with protein and fibre, not a sugary drink. See our guide on getting enough protein in an Asian diet.
5. Keep hydrated with water, plain tea or black coffee. In our heat, fasting windows can quietly turn into mild dehydration.
6. Review after four weeks. Are you sleeping, focusing and training well? If not, stop.

And if a fixed window does not suit you, the same benefits usually come from the basics: fewer sweetened drinks, smaller rice portions, more vegetables and not eating in front of a screen. Our look at rice, carbs and blood sugar covers several.

This article is general information, not medical advice. Talk to a doctor or pharmacist before fasting if you are pregnant, breastfeeding, on medication (especially for diabetes or blood pressure) or managing any health condition.

Frequently asked questions

Is intermittent fasting better than calorie counting for weight loss?

Most trials find they produce similar weight loss when total calories are comparable. The best choice is whichever you can stick with. Some people find a time window easier than tracking; others find the opposite.

Does black coffee break a fast?

Black coffee and plain tea contain almost no calories, so most IF protocols allow them. Adding milk, sugar or creamer does add calories. Be mindful that coffee on an empty stomach bothers some people's digestion.

Is 16:8 fasting safe every day?

For many healthy adults it appears to be safe in the short to medium term. It is not appropriate for everyone, including those with eating-disorder history, pregnancy or diabetes medication. Long-term data on daily 16:8 remains limited.

Can intermittent fasting cause muscle loss?

Any weight loss can include some lean mass, and one 2020 trial of 16:8 raised this concern. Eating enough protein within your window and doing resistance training helps protect muscle.

Is intermittent fasting the same as Ramadan fasting?

No. Ramadan fasting excludes both food and water from dawn to sunset and is a religious observance. Most intermittent fasting plans allow water and zero-calorie drinks during the fasting period and are followed for health or weight reasons.

Sources

1. de Cabo R, Mattson MP. Effects of Intermittent Fasting on Health, Aging, and Disease. NEJM, 2019
2. Liu D et al. Calorie Restriction with or without Time-Restricted Eating in Weight Loss. NEJM, 2022
3. Harvard T.H. Chan School of Public Health: Diet review, intermittent fasting
4. Johns Hopkins Medicine: Intermittent fasting, what is it and how does it work?
5. World Health Organization: Healthy diet fact sheet