What does 12:12 fasting deliver compared with 16:8?
16:8 fasting demonstrably produces more weight and fat loss in healthy adults than 12:12, which showed no measurable effect after 8 weeks. If you want to achieve something with time-restricted eating, an eating window of 8 to 10 hours is worth considering.
After 8 weeks, 16:8 fasting produced clearly measurable results in healthy, untrained adults: body weight fell by 2.46% and fat mass by 8.65%, without any significant change in muscle mass or calorie intake. It therefore appears that the fasting window itself makes the difference, not simply eating less.
12:12 fasting showed no measurable change in weight, fat mass or cardiometabolic values in the same study over the same 8 weeks. For anyone whose goal is weight loss, a 12-hour eating window seems to offer little benefit.
For people who already have obesity or metabolic syndrome, the picture is somewhat different. An eating window of 8 to 10 hours appears to offer the best balance between metabolic benefit and long-term adherence in that group. In people with metabolic syndrome, long-term blood sugar (HbA1c) fell by 0.10% after three months, on top of standard medication-based care. That is statistically demonstrable, but modest.
An eating window of 12 hours or longer scores better on adherence, but may at the same time be associated with disruption of the body's day-night rhythm, which in turn may increase the risk of obesity and metabolic problems. That relationship has not yet been established as cause and effect, but it is a reason to pay attention to the timing of eating as well, not just the duration.
Across all fasting methods combined, fasting produces weight loss compared with unrestricted eating. Compared with straightforward calorie restriction the advantage is small, and in studies lasting longer than 24 weeks that small difference largely disappears. The shorter eating window of 16:8 therefore performs better than 12:12, but is no miracle cure compared with other forms of dieting.
The direct comparison study between 12:12 and 16:8 in healthy adults comes from a single randomised trial of 8 weeks. Broader insights into time-restricted eating come from multiple randomised studies and two systematic reviews of the existing literature. The researchers of the broader systematic review rated the evidence for most outcomes as moderate certainty; on a scale from certain to uncertain, that sits in the middle. The blood sugar outcome in metabolic syndrome is likewise rated as moderate certainty. This means the findings are plausible, but that future research may still refine them.
Does it matter what time of day I eat?
Eating earlier in the day is more favourable for your weight, blood sugar and hormone balance than eating late or at night. The effects have been demonstrated in studies in people, but average weight loss is small: around 1 to 2 kg.
I am overweight: what will losing weight do for me?
Losing weight delivers measurable health gains from as little as 5% weight loss: better blood sugar, lower blood pressure and less pressure on your knees. Combine diet with strength training to preserve muscle mass and reduce the risk of weight regain.
What is NAD+ and why does it decline as you age?
NAD+ measurably declines with ageing, and supplements raise levels demonstrably in people. Whether that also makes you healthier has not yet been proven, and the safety of taking them for many years deserves attention.
Does my metabolism really slow down as I get older?
Your metabolism does not slow down from your thirties onward, but after your sixties energy expenditure does decline noticeably. Muscle loss and reduced physical activity are the biggest culprits, and these are also the areas where you have the most influence yourself.
Does the 16:8 schedule work better than other forms of intermittent fasting?
16:8 works better than shorter fasting windows in the short term, but over the long term it is not demonstrably better than simply eating fewer calories. Choose the approach you can sustain best.
Does a fasting-mimicking diet work better than simply eating less?
A fasting-mimicking diet has promising effects on several health markers, but whether it works better than simply eating less has not yet been demonstrated. If you want to try it, be aware that independent long-term data are still lacking and that the costs of commercial packages are a real consideration.