16/8 intermittent fasting and eating in the evening. What the evidence says

With 16/8 fasting you eat within an 8-hour window, for example from 12:00 to 20:00, and you don't eat for the other 16 hours. There are other forms of intermittent fasting, such as 5:2, with two days a week on very few calories, or alternate-day fasting. The question is whether they do anything more than a simple diet with fewer calories.

What the large reviews say

The Cochrane review of February 2026 brought together 22 randomised trials with 1,995 adults with overweight or obesity, followed for 6 months or more. Compared with standard dietary advice, intermittent fasting made little or no difference to weight loss, about 0.3 percentage points, with low certainty. For side effects the difference was also small, with very low certainty. The authors conclude that the choice is best made on the basis of what a person can keep up in practice.

A 2025 analysis in the BMJ, with 99 trials and 6,582 adults, found that all forms of fasting and daily calorie reduction lowered weight compared with changing nothing. Time-restricted eating, such as 16/8, was no better than daily calorie reduction. Only alternate-day fasting gave slightly more, about 1.3 kg, and not in the trials that lasted 24 weeks or more.

The UK's NICE looked at intermittent fasting in its 2025 guideline and made no recommendation for or against it. It said that for most outcomes fasting was not effective, and it called for more research.

Trials with an eating window

The trial in China gives the clearest answer. When calories were the same, the timing added almost nothing. This is fairly certain. In the Chicago trial, 16/8 worked as well as calorie counting, because participants ate less with both approaches. In the first trial, in the group that was measured precisely, 16/8 lowered fat-free mass in the arms and legs slightly more. This finding comes from a small group, but it is a reason to keep an eye on your protein.

Does eating in the evening make you put on weight?

If you eat dinner at 9 or 10 in the evening, this section is for you.

• A study in Spain of 420 people on a 20-week programme linked a late lunch, after 15:00, with less weight loss, 7.7 kg against 9.9 kg. Dinner time made no difference. Those who ate before 21:30 and those who ate after it lost about the same, 8.7 and 8.8 kg. The study did not assign meal times at random, so it does not show cause.
• Big breakfast or big dinner, at the same calories: in 30 adults, weight loss was the same. With the big breakfast they felt less hungry.
• In a small laboratory study of 16 people, the same food eaten 4 hours later increased hunger and slightly lowered the energy they used while awake, by about 59 kcal a day. The study lasted a few days and cannot tell us what happens to weight.
• Two reviews of trials found that when calories are moved earlier in the day, slightly more weight is lost, about 1.2 to 1.8 kg. The researchers behind one of them describe this as small, and in that review 22 of the 29 trials had a high risk of bias.

Overall, the evidence does not show that dinner at 9 or 10 ruins a diet. The day's calories come first. Eating more earlier may help a little, mainly because you feel less hungry. The finding is of low certainty.

Fruit in the evening

In October 2026 we searched for trials looking at fruit in the evening and body weight. We found none. The only related study we found is a large observational study of 133,468 adults in the US, followed for up to 24 years. Each extra daily serving of fruit was linked with about 0.24 kg less weight gain every 4 years. The time of day was not examined. So we know nothing certain about fruit in the evening, and we found no evidence that it makes you put on weight.

If you want to try 16/8

• Choose a window that suits your day. If you eat dinner at 9, a window from 13:00 to 21:00 is easier than an early one.
• Keep the same calories and the same protein as before. With two meals instead of three, the protein in each meal needs to be higher. See how much protein you need.
• If within a few weeks it makes you eat more in the evening or think about food all the time, stop and cut calories another way.

Orthodox Church fasting is a different thing. For that, see the article on fasting and protein.

Who should not fast on their own

• Diabetes treated with insulin or sulphonylureas: in a trial of people with type 2 diabetes, two days a week on 500 to 600 kcal doubled hypoglycaemic episodes, even though medicines were reduced. The trial was on 5:2, not 16/8, so this is indirect evidence. Talk to your doctor first. The same applies if you take SGLT2 inhibitors.
• Pregnancy: there are only small trials with a window of up to 10 hours and medical supervision. They showed no benefit for blood sugar, and in one of them the women were hungrier in the evening. Do not fast on your own.
• Breastfeeding: no fasting.
• An eating disorder now or in the past: in 2,762 teenagers and young adults in Canada, intermittent fasting was linked with eating disorder symptoms. The study does not show cause, but fasting is not a good idea in this situation.
• Under 18, low body weight, frail older people, or medicines that must be taken with food: talk to your doctor first.