Three o’clock, a deadline at five, and a chocolate bar in the desk drawer: sugar is a familiar answer to the afternoon slump, and it is the fix the research most clearly rules out. A 2019 meta-analysismeta-analysis: A study that combines the results of earlier studies on the same question into one overall estimate. Pooling makes the estimate more precise, but it cannot repair the studies it pools: a meta-analysis of surveys is still survey evidence.Full entry in the glossary pooling 31 studies found that carbohydrate gave no lift in mood at any point after eating, and within the first hour people felt more tired and less alert than after a placebo.¹

So how to eat for energy comes down to a few modest habits, not a special diet. Most of the research behind them is short studies and official advice rather than long trials, so each habit below carries its own grade:

1. Eat at regular times instead of going hours hungry
2. Skip sugar as a pick-me-up
3. Keep lunch moderate and plan around the afternoon dip
4. Build meals from whole foods, not sugary extras
5. Drink water through the day
6. Get tested before you take supplements

When tiredness lasts all day rather than just the afternoon, the wider picture is in the guide to why you might feel tired all the time; this page stays with food.

A sweet snack is a poor pick-me-up

A dose of sugar does not make people feel more energetic, according to a 2019 review by psychologists in Germany and the UK, led by Konstantinos Mantantzis, that pooled studies comparing carbohydrate with a placebo.¹

The study

Moderate evidence

Sweet dose or placebo: 31 studies of carbohydrate and mood, pooled in 2019

The team pooled studies in which people took carbohydrate or a placebo and then rated their mood. Carbohydrate had no positive effect on any aspect of mood at any time point after eating. Within the first hour it was linked to more fatigue and less alertness than the placebo.¹

The finding cuts against a belief many people hold from childhood. Its weak spot is scope rather than design: the studies compared one-off doses with a placebo, so the result does not speak to fueling long exercise or to sugar eaten as part of a mixed meal.

Why sugar leaves people flatter is not settled. The popular story is a spike followed by a crash below normal, but in healthy people blood sugar spends only a small share of the day in the low range, as the monitoring study further down shows. The lesson holds whatever the mechanism: the afternoon chocolate bar may be pleasant, but the research gives no reason to expect a sharper hour afterward, and some reason to expect a slightly sleepier one.

The afternoon dip arrives even without lunch, and a carb-heavy lunch can deepen it

Food explains only part of the mid-afternoon slump. A 2005 review by Timothy Monk at the University of Pittsburgh Medical Center in the US concluded that the post-lunch dip is real, can occur even when people have had no lunch and do not know the time, and has its roots in human biology, possibly in the body’s daily clock. A lunch heavy in carbohydrate, he wrote, deepens it.³

That changes what to do about it. If the dip were only about digestion, skipping lunch would cure it; because it can come without any lunch, skipping the meal is no reliable fix. The review also notes that the dip shows up for some tasks and some people rather than everyone, and the size of an ordinary lunch has been studied less, so treat “a big meal makes it worse” as plausible rather than proven.

In an ordinary week it can look like this: the early-afternoon meeting after a big bowl of pasta and a dessert feels like wading through fog, while the same meeting after a lighter lunch feels only a little slow. Both days have a dip; one has a deeper one.

The lesson is to plan around the dip rather than fight it with sugar. Keep lunch to a size that leaves you comfortable, put your most demanding thinking in the late morning where you can, and save routine tasks for early afternoon. A brisk walk after lunch is another option: a short bout of activity gives many people a brief lift in energy, as the research on exercise and energy shows.

How to eat for energy in an ordinary working day

Six low-risk habits cover what the evidence supports for healthy adults. They are general habits, not a treatment, and the support behind them ranges from a pooled analysis of controlled studies to plain official advice.

1. Eat at regular times instead of going hours hungry

The UK’s NHS, in advice last reviewed in 2023, suggests eating regular meals and healthy snacks every 3 to 4 hours, rather than a large meal less often, to keep energy up through the day.⁴ This is guidance rather than the result of trials on energy. In practice it might mean breakfast, lunch and an afternoon piece of fruit or yogurt spaced a few hours apart, instead of coffee alone until a late, large lunch. On breakfast itself, a 2016 review of studies in adults found eating it linked to slightly better memory afterward, with mixed results for attention and other thinking skills.⁵ If you are not hungry early, a later first meal is fine; people who fast for religious reasons can apply the same idea to the hours when they eat.

2. Skip sugar as a pick-me-up

Beyond the lack of any lift, the World Health Organization, in its healthy-diet fact sheet updated in 2026, advises keeping free sugars, those added to food plus the sugar in honey, syrups and juices, to less than 10 percent of daily energy, and notes that 5 percent or less may bring further health benefits.⁶ If you are hungry mid-afternoon, fruit, a handful of nuts or yogurt makes a snack; a sweet drink taken on its own is the one option the evidence argues against.

3. Keep lunch moderate and plan around the afternoon dip

Eat enough to feel satisfied, not stuffed, and plan the early afternoon for work that tolerates a dip. That might be soup and a sandwich rather than a second helping, with the report review moved to late morning and the inbox saved for after lunch. Skipping lunch is no reliable cure, since the dip can arrive without it.

4. Build meals from whole foods, not sugary extras

The WHO recommends a varied diet of mostly unprocessed foods, including fruit, vegetables, whole grains, legumes and nuts, with at least 400 grams of fruit and vegetables a day.⁶ Many national food guides say much the same, so check your own country’s version. The evidence for this pattern is about long-term health; its effect on daytime energy has not been tested directly.

5. Drink water through the day

The NHS notes that mild dehydration alone can leave you feeling tired, and that a glass of water will often help.⁴ Unless a doctor has asked you to limit fluids, sip through the day. Needs vary with heat, activity and body size, as the guide to how much water you really need explains. Coffee counts toward fluids too, within the limits set out in how much caffeine is too much.

6. Get tested before you take supplements

When tiredness lasts, a blood test beats a guess. In a 2012 randomized trialrandomized controlled trial: A study that assigns participants to the treatment or the comparison group at random, so the groups start out alike and a difference in what happens next can be put down to the treatment. Random assignment makes the two groups comparable; it does not make the people in the trial representative of anyone else.Full entry in the glossary in France of 198 women who reported fatigue and had low iron stores but no anemia, fatigue scores fell by nearly half on daily iron tablets over 12 weeks, against under a third on placebo.⁷ Because the women were tested first, the result says nothing about iron for people with normal iron stores. The UK’s NHS warns that high doses of iron can cause side effects such as constipation and stomach pain, and that very high doses can be fatal, particularly for children, so keep iron supplements out of their reach.⁸ Under a 1994 US law, the FDA has no authority to approve dietary supplements before they are sold, and rules differ elsewhere, so talk to a doctor or pharmacist before starting one.⁹

WiserHours

A steadier-energy eating day

• A first meal once you are hungry, then something every few hours
• No sweet drink or sweet snack eaten on its own as an energy fix
• A lunch that leaves you satisfied, not stuffed
• Fruit, vegetables, legumes, nuts or whole grains in most meals
• A glass of water with each meal and after exercise
• Demanding work in the late morning, routine work after lunch
• A short walk after lunch when you can
• A doctor, not a supplement shelf, if tiredness lasts for weeks

Find this checklist online:
https://wiserhours.com/energy/eat-for-energy/#checklist-eat-for-energy-day

Rises in glucose after meals are normal, not a warning sign

In people without diabetes, blood glucose rises after a meal and settles again, staying in the normal range for almost all of the day. A 2019 US study fitted 153 healthy children and adults with continuous glucose monitors and found that the typical participant’s readings sat between 70 and 140 mg/dL (3.9 to 7.8 mmol/L) about 96 percent of the time. Brief rises above that range and short dips below it happened too, so a healthy day includes them.¹⁰

That matters because wellness media often present every rise after a meal as a “spike” that drains your energy. Glucose monitors are mainly used by people with diabetes who need insulin, and a curve on a phone does not tell you how alert you feel.

Responses do differ between people. A 2015 study by a team at Israel’s Weizmann Institute of Science monitored 800 people for a week and found that responses to identical meals varied widely from person to person, then built an algorithm to predict each person’s response.¹¹ It measured glucose, not energy or alertness. That leaves a real evidence gap: none of the studies behind this article show that flattening normal glucose rises gives healthy people steadier energy.

Myth

Every glucose spike after a meal drains your energy.

Fact

In healthy people, glucose rises after meals and returns to the normal range. A 2019 monitoring study found this pattern normal, and none of the studies here link it to tiredness.

Unless a doctor has asked you to monitor, judge a meal by how you feel and work in the two or three hours after it, not by a curve. If tracking numbers about your food leaves you anxious or cutting out more and more foods, mention it to a doctor.

Each habit, graded by its evidence

The table grades each habit by the strongest evidence behind it. Only the sugar row rests on a pooled analysis of controlled studies; the rest lean on official advice, single studies or indirect evidence.

Shaky spells, lasting tiredness or food worries: who to call and when

Tiredness that lasts for weeks despite sensible eating needs a doctor’s appointment, and a few signs need help at once. These routes draw on the UK’s NHS (pages reviewed in 2023) and on crisis services in several countries; outside the UK, use your own doctor and local emergency number.

• Immediately: if someone with suspected low blood sugar stops responding normally or passes out, call your local emergency number (999 in the UK, according to the NHS).² If thoughts about food, weight or anything else turn to suicide or self-harm, get help straight away through your local emergency number or a crisis line: 988 takes calls and texts in the US, Samaritans (UK and Ireland) answers on 116 123, and Find A Helpline lists free lines in many other countries.¹²¹³¹⁴
• Soon: book a GP or family-doctor appointment if you have been tired for a few weeks for no obvious reason, or if weight loss or other symptoms come with it, as the NHS advises.¹⁵ The NHS also points people without diabetes who keep having low-blood-sugar symptoms, such as shaking, sweating or a fast heartbeat, to a GP.² If food rules, tracking or bingeing are taking over your days, talk to a doctor; the UK eating disorder charity Beat runs a helpline, and elsewhere a doctor can point you to local services.¹⁶
• Routine: at a regular appointment, bring up any plan to take supplements, or to change how you eat while pregnant or living with diabetes or kidney disease.

The bottom line

Eating for steady energy is less about finding the right food than about avoiding the wrong habits: long hungry stretches, sugar as a rescue and heavy, carb-laden lunches. Expect some afternoon dip whatever you eat, treat ordinary glucose rises as normal, and if tiredness lasts for weeks, see a doctor and get tested rather than guessing with supplements.