Afternoon fatigue may signal unbalanced glucose levels, a doctor warns. Dr Rangan Chatterjee, the bestselling author and host of the health podcast Feel Better, Live More, says the common 3pm slump is often dismissed as normal tiredness but can be an early metabolic warning sign.
His warning comes alongside a survey of 2,000 UK adults carried out by Abbott’s Lingo, a biosensor and app designed to help people track their glucose levels. The survey found that more than half of those who experience a post-lunch dip suffer from fatigue, a third report low mood and a quarter feel irritable. On average, Britons experience the slump three times a week. Yet only 15 per cent connect the way they feel to the food they eat; most blame stress (38 per cent) or poor sleep (34 per cent).
Dr Chatterjee said: “We’ve normalised feeling exhausted, unfocused and irritable, but these can be early signs that the body is struggling metabolically, and that matters.”
The science behind the slump
Glucose is the brain’s primary energy source. When levels drop sharply, the chemical messengers known as neurotransmitters – which carry information between brain cells – stop working properly. This disrupts the regulation of mood, concentration, memory and sleep, leading to the brain fog and poor focus that define the mid-afternoon dip. Key neurotransmitters such as serotonin, dopamine and norepinephrine are particularly affected, and even mild dehydration – more than three-quarters of the brain is water – can impair their production and signalling, compounding the problem.
The 3pm slump is partly driven by the body’s natural circadian rhythm, a 24-hour internal clock that creates a trough in alertness during the early afternoon. But a glucose crash can worsen that natural dip, prompting urgent signals from the body to replenish energy quickly. These signals often trigger cravings for sugary, high-carb foods. Dr Chatterjee warns that giving in to those cravings is counterproductive: it causes another glucose spike followed by another crash, trapping people in a cycle of energy swings.
Over time, persistently high blood glucose levels increase the risk of prediabetes. Dr Chatterjee notes that prediabetes – a condition that can progress to type 2 diabetes if untreated – is “far more common than most people realise and often develops silently”. An estimated 6.3 million people in the UK now live with prediabetes, many unaware of it. In total, one in five adults in the UK – more than 12 million people – have either diabetes or prediabetes, a situation he describes as a “hidden health crisis”.
Disruptions to the circadian rhythm from factors such as artificial light at night, irregular sleep schedules or shift work can make the afternoon slump more persistent, but a glucose imbalance remains a key and modifiable driver.
How to break the cycle
Dr Chatterjee advises that the slump can be managed through a combination of dietary changes and simple lifestyle habits. Lunches that lack protein or fibre can exacerbate the dip, so he recommends including a substantial serving of protein – such as meat, eggs or fish – to provide sustained energy. A small handful of nuts also helps: their healthy fats and protein slow digestion and the rush of sugar into the bloodstream, offering a slow-burning fuel source that stabilises energy levels. Other foods known to help regulate blood sugar include leafy greens, non-starchy vegetables, berries, seafood, beans, lentils, eggs and whole grains such as oats.
Hydration matters too. Drinking a glass of water can boost energy because even mild fluid loss affects brain function and nutrient circulation. Beyond diet, a brisk 10- to 20-minute post-lunch walk helps the body regulate glucose levels. Muscles use glucose for energy during walking, which lowers post-meal blood sugar spikes and aids digestion, circulation and mood.
Avoid reaching for caffeine or a quick sugar hit to avert the slump, Dr Chatterjee warns. These may offer a temporary lift but ultimately perpetuate the cycle of spikes and crashes that leaves people stuck in persistent fatigue, low mood and irritability.