PROFESSOR ROB GALLOWAY: Why I’m eating ALL my calories within this eight-hour window. And if you want to lose weight, trim your waist and balance your blood sugar, read on…

 We all know that what we eat has a massive impact on our health.

But now there’s evidence that our diet – more specifically, the timing of our meals – could actually help treat serious illness and potentially prevent conditions such as dementia.

For people like me with gut-related problems, this is potentially huge.

I have lived with Crohn’s disease since my early 20s, although it took years before I was diagnosed and for a long time I put my symptoms down to stress. But that’s a story for another day.

My symptoms include abdominal pain, fatigue and diarrhoea.

Needing the loo six to ten times a day is difficult enough at home – let alone at work – so the idea that changing when I eat, rather than what or how much, could ease my symptoms is exciting.

And this is what a study recently published in the journal Gastroenterology seems to suggest.

It found that when people with Crohn’s disease changed just their mealtimes – ie they weren’t asked to give up specific foods or cut calories – their symptoms improved significantly.

While this finding is important for me and others with an inflammatory bowel condition, the implications and potential benefits extend to all of us.

The research, from the universities of Calgary and British Columbia, both in Canada, looked specifically at the effect of time-restricted eating (TRE) – where you have your meals within a set number of hours each day – on patients with Crohn’s.

In a 12-week trial, 20 of the 35 participants (who were all obese) ate within an eight-hour window (for example 10am to 6pm) for six days a week; the rest continued their usual eating patterns.

Despite the two groups reporting a similar quality diet and calorie intake, the fasting group lost an average of 2.5kg (5.5lb), while the others gained about 1.7kg (3.7lb).

In addition, scans showed a reduction in the fat surrounding internal organs in the fasting group, compared with an increase in the others.

The TRE group also experienced beneficial changes in their gut bacteria, including a more varied mixture of microbes and an increase in some bacteria that produce substances known to help regulate inflammation. Plus, they had significant changes in three proteins linked to fat tissue, inflammation and the immune system.

Crucially, these included leptin – which is produced mainly by fat cells and helps control appetite, but also plays a role in regulating immunity.

While we don’t understand for certain why TRE had this effect on gut microbes and inflammation, having regular periods with no food may alter the balance of the bacteria, encouraging those that produce substances that help regulate inflammation.

But we do know that excess inflammation is central to Crohn’s and other types of inflammatory bowel disease – tellingly for me, the TRE group reported a 40 per cent fall in bowel movements and a 50 per cent reduction in abdominal discomfort – improvements not seen in the control group.

Despite this being a small preliminary study, the findings highlight how our body clock does much more than determine when we feel sleepy; it’s crucial for our digestion, hormone release and blood-sugar control.

And eating within a restricted window and avoiding food late in the evening, may help us work with our body clock rather than against it – for instance, our bodies are generally more sensitive to the hormone insulin earlier in the day and therefore better able to deal with a rise in blood sugar after a meal.

We know that disrupting these rhythms can matter because people who work night shifts have higher rates of obesity and metabolic disease, such as type 2 diabetes.

Major proof for all this came in an analysis of 41 trials, published in BMJ Medicine earlier this year, which found that TRE improved weight, waist size, blood sugar and insulin levels, compared with usual eating patterns.

But perhaps more interestingly, those who ate earlier in the day generally did better than those who ate later – losing about 1kg more and having lower insulin levels. However, simply making the eating window shorter and shorter did not consistently produce better results.

The idea that restricting when we eat can be beneficial makes evolutionary sense.

In the past, we would only be able to eat after we had successfully hunted prey. But now we have high-fat, high-sugar food available 24/7.

The first real clue about the impact of fasting came in a landmark study published in 2012, that showed that mice fed a high-fat diet but only allowed to eat within an eight-hour window were protected against obesity, high insulin levels, inflammation and fatty liver.

More recently, researchers at the University of Texas Southwestern Medical Centre looked at the impact of TRE on ageing in mice and found that those limited to eating to either eight or 12 hours were less frail and had less body fat – while the males also aged more slowly (why males only is not clear), reported Nature Aging in June.

But not every study has been as positive. Most notably, a review by the authoritative Cochrane group earlier this year found that intermittent fasting produced little or no more weight loss than conventional dietary advice.

This prompted ‘fasting doesn’t work’-type headlines – but the fact is, the participants still lost weight. Plus, the review did not look at whether timing might have benefits for metabolism, inflammation and the gut.

For me, time-restricted eating seems to have potential to improve metabolic health and reduce some of the processes linked to inflammation, which is relevant to all of us because inflammation is contributory to chronic conditions including heart disease, stroke and dementia.

So after reviewing all the research, I’m going to try and keep my calories within an eight-hour window – from 10am to 6pm. Because it’s not just what you eat that matters, but when.

NOTE: Don’t try TRE if you are pregnant or lactating – and if you have any medical condition, speak to your GP first.

@drrobgalloway