Eating dinner too late is wrecking your gut, heart and brain health

We know that eating a packet of crisps or a bowl of ice cream before bed isn’t great for our health, but avoiding those late-night snacks may be more beneficial than you realise.

A recent study found that avoiding food in the hours before you go to bed may help to stave off cognitive decline in older age. Researchers studied 47 overweight or obese women aged 50 to 79, all of whom were asked to reduce their diet by 500 calories a day for six months, with one group eating over a 12-hour period and another eating from 10am to 6pm.

Both groups lost an average of 7kg (15lb), but those who finished eating at 6pm performed better in spatial planning and problem-solving tests, with some evidence of improved memory and learning.

“This research adds to a growing body of evidence that the time of day that we eat our food matters as well as the eating window [the time between your first meal and your last],” says Sarah Berry, a professor of nutritional sciences at King’s College London and chief scientist at nutrition data company Zoe.

Why timing matters more than what you eat

Unfortunately, swapping biscuits or crisps for something healthier might not be enough. One study published in the European Journal of Nutrition, found that snacking late at night was associated with unfavourable health outcomes such as increased body fat and blood sugars, even if people were eating healthy snacks.

Eating four hours before bed (around 6pm) gives your body enough time to fully digest food, cool down and begin its reparative processes. “Our bodies are finely tuned to operate on a roughly 24-hour cycle called our circadian rhythm,” Prof Berry explains. “It governs all our bodily processes, from the gut to the brain and everywhere in between. Eating outside our natural rhythms is one of the primary reasons late-night eating can cause problems.”

Here, Prof Berry explains the detrimental effects of late-night eating on our bodies, and shares her tips to minimise the damage.

How eating after 6pm impacts your health

Brain

As the recent study demonstrates, eating your last meal earlier could protect against cognitive decline. “Although there’s a limited amount of direct evidence,” says Prof Berry, “eating later in the evening might have a negative impact on brain health.” Eating later could disrupt the brain’s signals, disrupt our sleep and stress hormones, as well as increase inflammation in the brain.

Eating late is also known to disrupt your deep sleep, which is when our brains consolidate memories and clear out toxic waste that can lead to cognitive decline. However, deep sleep only occurs when the body cools sufficiently. If food is still being metabolised, this increases your core temperature, delaying or reducing the amount of deep sleep.

“We know from large population observational studies that people who eat later in the day are more likely to have higher blood pressure, potentially higher cholesterol, higher rates of type 2 diabetes,” says Prof Berry, all of which can increase the risk of vascular dementia.

“However, late eaters often have a less healthy diet quality, so it is difficult to tease apart the effects of a less healthy diet from the timing of eating on brain health until rigorous clinical trials have been conducted,” Prof Berry adds.

Heart

“Consistently eating late at night over many years is linked to disturbed sleep, greater body weight, disturbed metabolism, higher levels of inflammation and poorer blood lipid profiles, all of which can increase your chance of developing heart disease,” says Prof Berry. “Specifically, studies show that levels of blood triglycerides [a type of fat] are higher after meals eaten late in the day compared to earlier in the day, and this may increase risk of heart disease.”

Late eating also prevents your blood pressure from dropping to the levels it normally would during sleep, causing strain on the heart.

There is a growing body of evidence linking late eating to a higher risk of heart-related diseases, such as stroke. An ongoing study launched in 2009 in France, which published its findings in the medical journal Nature Communications in 2023, followed 103,389 adults who completed 24-hour dietary records over several years. Eating their last meal after 9pm, rather than before 8pm, was linked to a 13 per cent higher risk of developing cardiovascular disease. For stroke and transient ischaemic attack, eating after 9pm was associated with a 28 per cent higher risk than before 8pm.

Gut

Research suggests that eating a heavy meal late at night can disrupt the gut microbiome and increase the risk of acid reflux.

“Like the rest of your body, your gut microbiome also has a circadian rhythm,” says Prof Berry. “For instance, certain species [of gut bacteria] are busier during sleeping hours, cleaning up the mess left behind from the day. Eating late can interrupt their work, leaving their cleaning job undone.” Additionally, if your body expects food at a certain time, it releases digestive enzymes and stomach acid, but disrupting this rhythm can cause indigestion.

There’s also an increased risk of acid reflux: when you lie down after a meal, the stomach’s contents push acid up into the oesophagus, causing heartburn.

Immune system

“Because the gut microbiome plays such an important role in supporting and guiding the immune system, late-night eating may interrupt immune responses and promote systemic inflammation,” Prof Berry says.

Additionally, our immune system has a strong circadian rhythm, which if disrupted can cause low-grade inflammation. “We know that long-term inflammation underpins many chronic diseases [such as type 2 diabetes and cancer]. However, we need more clinical trial data to piece together the multiple complex systems at play to determine if there is a direct effect of late-night eating on immune and inflammatory responses,” Prof Berry adds.

Weight

“There is good evidence suggesting that eating late at night is associated with an increased risk of weight gain and obesity,” says Prof Berry. “Interestingly, the same meal eaten later in the day has been shown to induce less fullness hormones compared to if eaten earlier in the day. This is likely to be due to how metabolism works differently across the day, dysregulation of appetite hormones, and the gut microbiome.”

Similarly, evidence suggests that people who eat more of their calories earlier in the day are more likely to lose weight than those who eat more calories later in the day, even if their overall caloric intake is the same.

“For many of us, though,” says Prof Berry, “if there is a link between late-night eating and our weight, it may have more to do with what, how and why we’re eating at those times, rather than the when – and the fact that late night eating impacts sleep, which also indirectly impacts our weight.”

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