How the ‘8-hour rule’ could keep your brain ‘pincer sharp’ after 50 – and it’s got nothing to do with sleep

You know how career success is often down to who you know, not just what you know? Well, when it comes to health and wellbeing, there’s a similar rule. It’s not just what you eat, but when you eat it.

That’s a suggestion backed up by a new – small, so do take it with a pinch of salt – study that looked at the benefits of eating all your meals in a daily window of eight to nine hours, rather than spread out longer throughout the day. The research, from Rutgers University, found that women over the age of 50 who followed this ‘eight-hour rule’ performed better on problem-solving tests, pointing to a potential brain health boost.

What are the potential benefits of the ‘eight-hour rule’?

The study followed 47 women participating in a six-month weight loss programme, all of whom had been guided to cut 500 calories from their daily diet. 26 women of the 47 were also instructed to eat all their food within a period of less than nine hours a day, while the rest were able to eat whenever they wanted. Those in the time-restricted group had an average eating period of 8.2 hours a day, generally between 10am and 6pm, while the latter group ate over the course of an average 12.3 hours. In six months’ time, all the women lost a similar amount of weight, but those who had kept their eating within an 8-9 hour period performed significantly better on tests that measured planning and problem-solving. They also tended to make fewer mistakes.

The researchers noted that bigger studies will be needed to confirm a link between following the eight-hour rule and improved cognitive skills, and to explore the ‘why’ of this relationship. ‘Losing weight alone will ward off some of the ageing-related cognitive decline, and these data suggest that there may be additional benefits if you stop eating 4 hours prior to going to sleep and reduce food intake to 8-9 hours per day, compared to the usual eating window of 12 hours per day,’ said Sue Shapses, who led the study. ‘These outcomes suggest a better ability to remember information during everyday tasks and reducing mistakes related to memory, attention and problem-solving. Reductions in the eating window predicted greater improvements.’

And interestingly, this isn’t the first study to suggest we restrict the times we eat to an eight-hour window. Research from the University of Surrey found that participants who delayed their first meal of the day by an hour and a half, then ate their last meal of the day an hour and a half earlier, ended up consuming fewer calories. There’s also evidence to suggest that eating dinner earlier (say, before 6pm) can lower blood pressure and stabilise your insulin levels. Plus, it seems to improve your sleep.

‘Some research suggests that eating within an 8-9 hour window, often referred to as time-restricted eating, may have benefits for metabolic health,’ says registered nutritionist Rhiannon Lambert. ‘Some studies have found improvements in areas such as blood sugar regulation, insulin sensitivity and blood pressure in some groups of people, even when weight loss is minimal. Restricting the eating window may also naturally reduce overall calorie intake for some people, which can contribute to weight loss if that is a goal. There’s also growing interest in how meal timing interacts with our circadian rhythm, the body’s internal clock. Our metabolism tends to be better equipped to process food earlier in the day, so aligning eating patterns more closely with daylight hours may offer additional metabolic benefits.

‘That said, the evidence is still evolving. Many of the studies have been relatively small or short-term, and it’s not yet clear whether an eight-hour eating window is superior to other healthy eating patterns over the long term. Overall diet quality, food choices, sleep, exercise and other lifestyle factors remain just as important, if not more so.’

Should you try the eight-hour rule?

So, should we try following the eight-hour rule to keep our brains sharp and improve our physical health, too? The evidence isn’t solidly there just yet, but some dietitians do think that it’s worth a go – specifically by shifting your dinner earlier in the day to stick to that eight-hour window, rather than moving your other meals later, based on the research that links earlier breakfasts with increased longevity. You might, for example, say that you’ll only eat between the hours of 9.30am and 5.30pm.

‘The benefits are real, but modest,’ Dr Penelope Sheehan, a GP with a special interest in women’s health and preventative medicine at Medical Express Clinic, tells Good Housekeeping. ‘Research shows an 8-hour eating window can help with small weight loss, less fat around the middle, better insulin control and a slight drop in blood pressure. For many women, the main win is simpler: it stops late-night grazing. It’s not a magic fix, and it doesn’t clearly beat ordinary calorie control when you eat the same amount. Where it helps most is women who overeat in the evening and want a straightforward rule they can stick to.’

How to use the 8-hour rule

Whether you can embrace the 8-hour rule relies heavily on your health history and lifestyle, so it isn’t suitable for everyone. ‘It would not be recommended during pregnancy or breastfeeding, for children and adolescents, for active individuals or for anyone with a current or previous eating disorder, where restricting eating times could reinforce unhelpful behaviours,’ says Rhiannon. It’s also not recommended for people with diabetes, frail older adults and people on some medications that need to be taken with food, and may not be suitable for those with IBS or other gastric issue.

Hormonal changes can disrupt eating plans, too. Dr Sheehan says: ‘Cravings often spike in the week before a period, so a strict 8-hour window may not suit every week. That’s normal. Prioritise protein, sleep, and hydration.’ She advises getting a full blood test and speaking with your GP before diving in.

If you’re going to try it, it’s important to be realistic about whether this will work for you on a practical level. Only eating between 9am and 5.30pm will be tricky (and expensive) if you work full-time in an office without a proper kitchen.

Also, you know your body best. Tailor your 8-hour window to work best for you. If you know you’re absolutely ravenous first thing in the morning, heed your body’s hunger cues and consider shifting your eating period to earlier in the day. ‘The best eating pattern is ultimately one that is sustainable,’ notes Rhiannon.

‘Pick a window you can stick to over the long-term,’ agrees Dr Sheehan. ‘Both work: late breakfast to early evening, or breakfast and lunch with an early dinner. I slightly favour eating earlier and finishing by around 6-7pm, because trials show better blood sugar and blood pressure responses than saving most food for late evening. Don’t start with coffee and biscuits at 10am and have your last bite at midnight. Build a proper overnight fast. Start with a 10-hour window for a fortnight, then tighten to 8-9. Keep the first meal balanced with protein and fibre, and plan dinner so you’re not starving. It’s not about skipping breakfast by default, nor eating most of your calories after 8pm. Match the pattern to your life, but lean earlier if you can.’

Ensure that within your eating window, key nutritional needs are being met. Rhiannon advises: ‘Getting enough protein, fibre, fruit and vegetables, healthy fats and key micronutrients into a shorter eating window can be more challenging if meals are skipped or rushed.’ Ultimately, if the choice is between a more nutritious meal slightly later in the day and a handful of crisps pre-6pm, choose the later, nutritious meal every time.

And if you give the 8-hour rule a go and it doesn’t work for you, bin it! As Rhiannon puts it: ‘Time-restricted eating isn’t superior or magic! If someone enjoys it, feels well and it helps them establish a consistent eating routine, it may be a useful tool. But if it leads to low energy, poor concentration, disrupted training, increased negative associations with food or overeating later in the day, then it’s unlikely to be the right approach. There’s no single eating schedule that suits everyone.’