Intermittent fasting 16:8: does it help you lose weight?

In short: in trials, 16:8 intermittent fasting helps people lose weight about as well as ordinary calorie cutting, and not more. In a year-long NEJM trial, the gap between an eating window and a plain calorie deficit was not statistically significant². The window works mostly because people tend to eat less in 8 hours. If the schedule suits you, it is a perfectly good tool. If it ends in evening binges, there is no reason to hold on to it.

What 16:8 means, and the other schedules

16:8 means 8 hours when you eat and 16 hours with no calories. For example, noon to 8 p.m. In the TREAT trial, people had to avoid all calories from 8 p.m. until noon the next day¹.

It is one of several schedules. A 2025 BMJ meta-analysis sorts them into three groups⁴:

• time-restricted eating (a 16:8 window, 14:10, and similar);
• alternate-day fasting, where near-fasting days alternate with normal ones;
• whole-day fasting, such as the 5:2 plan.

What the trials found

In the Lin trial, both groups ended up eating less by almost the same amount: about 425 kcal a day with the window and 405 kcal with counting³. The window worked as a way to eat less without tracking calories.

The BMJ meta-analysis pooled 99 randomized trials and 6,582 adults⁴. Every fasting schedule and plain calorie restriction reduced weight compared with unrestricted eating. Against plain calorie restriction, only alternate-day fasting showed a small edge: −1.29 kg, with moderate certainty. In trials lasting 24 weeks or longer, the schedules no longer differed, and only the advantage over unrestricted eating remained. The authors conclude that intermittent fasting gives roughly the same results as ordinary calorie restriction.

Why it works, and why it is not magic

Weight changes through energy balance. A shorter window leaves less room for snacks, the evening tea and biscuits, and “one more plate”. That makes eating less easier for many people. But if a whole day’s usual calories fit into 8 hours, weight stays where it was. How that balance works is covered in calorie deficit in plain language.

One more detail from TREAT: among the participants tested in person, the window group lost more appendicular lean mass index (lean mass in the arms and legs) than the control group¹. It is one small trial, but the takeaway is familiar: whatever the method, protein and strength work matter. More in protein and fullness and home workouts for beginners.

Who should talk to a doctor first

• Diabetes treated with insulin or a sulfonylurea. These medicines lower blood glucose, and not eating enough carbohydrate lowers it further⁵. A long gap between meals on that treatment can lead to hypoglycemia. Agree any change to meal timing with the clinician who manages your diabetes.
• Pregnancy or breastfeeding. The trials above studied other people, and their results do not carry over.
• A current or past eating disorder. Strict rules about when eating is “allowed” can feed it.
• Teenagers. A growing body needs a different approach.

How to try it gently

1. Start with a 12-hour window, for example 8 a.m. to 8 p.m. If that feels comfortable after a week or two, narrow it by an hour or two.
2. Eat ordinary meals inside the window: protein, vegetables, normal portions. The window is not permission to eat anything. In the Lin trial, weight fell by about as much as calories fell.
3. Outside the window: water, and tea or coffee without sugar or milk.
4. If the window turns into evening overeating, irritability, or dizziness, widen it or drop the schedule. A slip is not a reason to restart on Monday: a gentle return after a slip.
5. Judge it by your average weight over 2–4 weeks, not one morning: why the scale jumps.

The bottom line

16:8 is one way to create a calorie deficit, not a separate weight-loss mechanism. In trials it does not beat ordinary calorie restriction, and it does not lose to it either. Pick the schedule you can keep for months: the one where you are less hungry and slip less often.

Common questions

Can I have coffee with milk before the window opens?

In the TREAT trial, nothing with calories was allowed outside the window¹. Milk has calories, so by the strict rule, no. A splash makes almost no difference to weight, but once the splash becomes a syrup latte, it is a meal.

Which is better, 16:8 or 5:2?

In the BMJ meta-analysis the differences between schedules were small, and in longer trials they disappeared⁴. The better schedule is the one you can stick to.

Is this the same as “no food after 6 p.m.”?

It is similar: another rule about timing. Why the clock alone does not decide much is covered in no food after 6 p.m.

Sources

1. Lowe D.A. et al. Effects of time-restricted eating on weight loss and other metabolic parameters: the TREAT randomized clinical trial. JAMA Internal Medicine, 2020;180(11):1491–1499.
2. Liu D. et al. Calorie restriction with or without time-restricted eating in weight loss. New England Journal of Medicine, 2022;386(16):1495–1504.
3. Lin S. et al. Time-restricted eating without calorie counting for weight loss in a racially diverse population: a randomized controlled trial. Annals of Internal Medicine, 2023;176(7):885–895.
4. Semnani-Azad Z. et al. Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis of 99 randomised trials. BMJ, 2025;389:e082007.
5. NIDDK: low blood glucose (hypoglycemia), and the medicines and habits that lower it.