Biscuits before bed may be off the menu.

For a quarter of people are undoing the benefits of healthy meals by snacking unhealthily, a study has suggested. 

Researchers from London, who monitored the eating habits of more than 850 people, found that one in four reported eating unhealthy snacks — such as chocolate, crisps and cakes — alongside ‘healthy meals’.

Results suggested that this group were ‘undoing the benefits’ of eating a nutritious breakfast, lunch and dinner, as eating junk food snacks were linked with having a higher BMI and blood sugar — raising their risk of strokes, heart disease and obesity.

However, analysis showed that snacking itself is not unhealthy — as long as the people chose healthy treats, such as fruit, nuts and seeds. 

The scientists tracked the snacking habits of 854 people from the ZOE PREDICT study, a group of in-depth nutritional research studies that aim to reveal how and why people respond differently to the same foods.

Participants consumed ‘standardised test meals’ over nine to 11 days and logged the quantity and types of snacks consumed using an online food diary. 

Some 95 per cent of cohort confessed to snacking, while the average daily intake was recorded at 2.28 snacks per days. 

Some 29 per cent of people ate more than two, researchers said. 

But writing in the European Journal of Nutrition, the scientists from Kings College London said 26 per cent of participants reported eating healthy meals but opting for ‘poor quality snacks’ which left them ‘feeling hungry’.

This group had ‘poorer health markers’. 

Snacking frequency, however, had no impact on blood fats and blood pressure. 

Dr Sarah Berry from King’s College London and chief scientist at ZOE said: ‘Considering 95 per cent of us snack, and that nearly a quarter of our calories come from snacks, swapping unhealthy snacks such as cookies, crisps and cakes to healthy snacks like fruit and nuts is a really simple way to improve your health.’ 

The most popular snacks consumed were cookies, fruit, nuts and seeds, cheese and butter, cakes and pies and granola or cereal bars, scientists said. 

High blood sugar and fat can lead to diabetes and heart disease, studies have found. 

People with diabetes are also more likely to have other conditions that raise the risk of heart disease, such as high blood pressure.

The researchers also found those who ate ‘high-quality snacks’ — like nuts, fresh fruit and granola bars — had ‘better metabolic health’ and were not as hungry. 

Ultra-processed foods like cakes, crisps and brownies generally have higher sugar, salt and saturated fat content compared with less processed foods.

The term covers food that contains ingredients that a person wouldn’t add when cooking at home — such as chemicals, colourings and preservatives.

These include ready meals, ice cream, sausages, southern fried chicken, cereals and ketchup.

They are different to processed foods, which are processed to make them last longer or enhance their taste, such as cured meat and cheese.

But researchers also found the timing of snacking was also crucial to health, with eating later at night carrying ‘significantly more negative health implications’. 

People who ate most of their snacks in the evening after 9pm saw larger spikes in their blood sugar compared to those snacked earlier in the day, they said. 

Those who snacked later also had higher concentrations of fat in their blood compared to those who snacked earlier.

Snackers at this time tended to eat energy-dense foods which were high in fat and sugar.

Dr Kate Bermingham from King’s College London and senior scientist at ZOE said: ‘This study contributes to the existing literature that food quality is the driving factor in positive health outcomes from food. 

‘Making sure we eat a balanced diet of fruit, vegetables, protein and legumes is the best way to improve your health.’

•  For those aged 75-90 sex didn’t have to be all that good – just frequent

By Sophie Freeman

Published: 20:28 EDT, 18 August 2023 | Updated: 20:52 EDT, 18 August 2023

Once upon a time, before the arrival of electric light, people would eat their evening meal by candlelight.

When my wife, Clare, and I are feeling romantic (or when there is a power failure), we still sometimes do this, although turning on an electric light is obviously far more convenient.

But perhaps the idea of going back to more candlelit dinners will catch on, thanks to recent research which suggests that reducing your exposure to bright lights in the evening can lead to better sleep, improve your blood sugar levels and even help you to lose a bit of weight.

On top of that there is evidence that exposure to bright light in the late afternoon and evening can trigger anxiety and mood swings in some people (but more on that later).

I’ve written before about the benefits of exposing yourself to bright light first thing in the morning, ideally by going for a brisk 30-minute walk or just spending a bit of time in your garden.

That’s because doing this helps reset your internal body clock, which regulates your circadian rhythms, and which, in turn, determines the timing of natural body processes and functions — including your energy levels and your sleep.

But what you do at the other end of the day also matters.

There is, for example, mounting evidence that being exposed to bright light in the evening not only disrupts your sleep but can lead to weight gain.

In a study, published in the journal PLOS One in 2016, researchers at Northwestern University in the U.S. took 19 healthy adults and asked them to eat their evening meal under either dim or bright light.

When the volunteers ate under bright light, this led to an increase in insulin resistance (which means their bodies had greater difficulty getting their blood sugar levels down after they’d eaten the meal).

The researchers said that increased insulin resistance and a build-up of blood sugar could, over time, lead to increased body fat, weight gain and a higher risk for type 2 diabetes. And pregnant women may be particularly sensitive to the impact of light; one of the unfortunate potential complications of getting pregnant is that some women develop gestational diabetes, where their blood sugar levels soar into the diabetic range.

In the UK around one in 20 pregnant women is affected, and although the condition often resolves once the baby has been born, if you develop gestational diabetes you’re ten times more likely to develop type 2 diabetes (as well as having a higher risk of cardiovascular problems and stroke) later in life.

Gestational diabetes also potentially affects the baby, increasing their risk of becoming overweight or having high blood pressure when they grow up. In a recent study of pregnant women, published in the American Journal of Obstetrics and Gynecology Maternal and Fetal Medicine, 741 pregnant women were fitted with a wrist device to measure their exposure to light — the researchers found the mothers-to-be who got the most exposure to bright light in the three hours before bedtime were at greatest risk of developing gestational diabetes.

This wasn’t a proper randomised controlled trial — involving a placebo group — but it certainly adds to research suggesting that late-night light exposure really can mess with our metabolism.

Dr Minjee Kim, an assistant professor of neurology at Northwestern University, who carried out this study, said all this research into light has affected how she lives her own life.

‘I’m now the light police at home,’ she says. ‘I switch off unnecessary lights and try to dim the light as much as possible. For evening activities such as dinner and bathing the kids, you don’t need bright light.’

She also recommends avoiding using your computer or phone during the lead-up to bedtime — ‘but if you have to use them, keep the screens as dim as possible’.

And as I mentioned earlier, light doesn’t just affect our blood sugar levels, it can also affect our mood.

Too little light in winter can lead to seasonal affective disorder (SAD), also known as the winter blues. As I know from personal experience, you feel depressed, moody and have a craving for carbs. Separately, too much light in the evening can affect people with Alzheimer’s.

If you have a loved one with this disease, you may have noticed that distressing symptoms such as confusion and anxiety become worse late afternoon and evening.

This is called ‘sundowning’ and a new study suggests it may be driven by changes in light levels.

Previously it was thought this behaviour was due to changes in the brain, but research in the journal Frontiers In Aging Neuroscience suggests it is changes in the retina, the light-sensitive area at the back of the eye, caused by Alzheimer’s, that are responsible. This understanding could poten-tially lead to new approaches to coping with sundowning.

In the meantime, Dementia UK recommends closing the curtains and turning on the lights before dusk ‘to ease the transition into night-time’.

Our remote ancestors rose with the dawn and huddled round the campfire at night.

So it’s not surprising that light, how much you are exposed to and when, has such a profound effect on our mind and bodies.