Short answer: Diet probably matters less than sleep for exams, but it helps. In small trials, low-GI breakfasts helped children’s late-morning memory, DHA sped up memory in young adults who ate little fish, and iron treatment helped iron-deficient women. Eat a low-GI breakfast, use caffeine moderately (under 400 mg a day), drink water and get your iron checked if you’re tired.

The best study diet is a low-glycemic breakfast, protein at every meal, oily fish a few times a week, enough water and moderate caffeine. The evidence is preliminary: small trials, mostly in children or specific groups, and no trial has tested a diet’s effect on exam results.

What to eat during exam season

  1. A low-GI breakfast before studying. Oatmeal with nuts and berries, eggs on whole-grain toast, or Greek yogurt with seeds and fruit. Skip sugary cereals, pastries and juice.
  2. Protein at every meal. About 20 to 25 grams is a reasonable target: eggs, Greek yogurt, canned fish, lentils, tofu or nuts.
  3. Caffeine in moderation. Many trials used 100 to 200 mg per dose, and it peaks 30 to 60 minutes after drinking. Stop eight to ten hours before sleep. Don’t exceed about 400 mg a day (200 mg if pregnant).
  4. Water through the day. Keep a bottle at your desk; aim for 2 to 3 liters of total fluid a day.
  5. Oily fish two to three times a week. Canned sardines, frozen salmon, walnuts and chia seeds are affordable.
  6. Check your iron if you menstruate or eat a plant-based diet and feel tired.
  7. Batch-cook once a week so you don’t fall back on instant noodles.
  8. Protect your sleep. It’s when the brain consolidates what you studied.

Breakfast: what you eat matters

A review of 36 studies in children and adolescents (Adolphus 2013) found that breakfast mainly helped on-task behavior in class. There was suggestive evidence that habitual breakfast and school breakfast programs improve academic performance, with the clearest effects on math grades in undernourished children. Factors such as family income and weak study methods may explain part of the link. Most of this research is in children, not university students.

The type of breakfast matters too. In 19 children aged six to seven (Benton 2007), memory and sustained attention two to three hours after a low-glycemic-load breakfast were better than after higher-glycemic-load breakfasts of similar energy. The children also showed fewer signs of frustration. In a crossover study of 64 children aged 6-11 (Ingwersen 2007), performance declined across the morning, but attention and memory fell less after a low-GI cereal than a high-GI one.

Glycemic load (GL) combines how fast a food raises blood sugar with how much you eat. Meals under 20 give a gradual rise; above 20, a faster rise and fall. A rough rule: if a carbohydrate is white, soft and dissolves quickly in your mouth, it’s almost certainly high-GI. If it needs chewing and has visible grains, seeds or fiber, it’s almost certainly lower-GI. Our article on breakfast and cognition covers this in more depth.

If you can’t eat early, the evidence on fasted study is mixed. A review (Dye 2000) concluded that carbohydrate at breakfast tends to improve morning performance, but the studies are rarely decisive. A small snack with some protein, such as nuts and fruit or a yogurt, within two hours of starting is a reasonable compromise.

Caffeine: how much and when

Lieberman (2002) gave 68 US Navy SEAL trainees 100, 200 or 300 mg of caffeine or placebo after 72 hours without sleep. The 200 and 300 mg doses improved vigilance, reaction time and learning, and the authors judged 200 mg optimal in those conditions. Higher doses are more likely to cause anxiety and jitteriness. See our caffeine and cognition guide for more.

In a survey of 1,248 US college students (Mahoney 2019), average intake was about 160-170 mg a day, mostly from coffee. Energy drinks were a larger source than in the general population. Some students drink far more around exams. Energy drinks contain about 80 to 300 mg per can, and the larger cans exceed the doses used in most trials.

Too much caffeine can cause anxiety, restlessness, a fast heartbeat and scattered attention. It also disrupts sleep. A systematic review (Clark & Landolt 2017) found caffeine typically lengthens the time to fall asleep, shortens sleep and reduces deep sleep, which is important for memory.

Caffeine’s half-life is about five hours, though it varies widely. A coffee at 4:00 PM means about half the caffeine is still in your blood at 10:00 PM. If you plan to sleep at midnight, stop by 2:00 to 4:00 PM. For evening study, try green tea, which has less caffeine, or a brief walk.

Water

Mild dehydration, a loss of 1 to 2% of body weight as water, has been linked to small drops in attention and working memory, mostly after exercise in the heat. In 26 young men (Ganio 2011), losing about 1.6% of body mass through exercise increased errors on a vigilance task and slowed working-memory responses. But a review (Benton 2011) concluded that results in young adults are inconsistent, with little evidence that dehydration in normal daily life disrupts thinking. The most consistent findings are in children, whose memory and attention improved after a drink.

Coffee and tea count toward fluids, but many students drink little plain water. Pale yellow urine suggests you’re drinking enough; dark yellow, or going more than four hours without urinating, suggests you’re not.

Omega-3 fats

Stonehouse (2013) ran a randomized trial in 176 healthy adults aged 18 to 45 with low DHA intake. Taking 1,160 mg of DHA a day for six months sped up episodic and working memory compared with placebo. Episodic memory accuracy improved in women and working-memory speed in men.

Two to three servings of oily fish a week, such as canned sardines or frozen salmon, provide DHA and EPA. Walnuts, chia, flax and hemp seeds provide a plant omega-3. Algae DHA supplements are an option if you don’t eat fish. Like other omega-3 supplements, they can increase bleeding risk in people taking blood thinners, so ask a doctor or pharmacist first if you take any medication. More in our omega-3 guide.

Iron deficiency

Iron deficiency is the most common nutritional deficiency worldwide, and female students are at higher risk because of menstrual losses. Iron carries oxygen to the brain and is needed to make dopamine and myelin.

In a placebo-controlled study of women aged 18-35 (Murray-Kolb & Beard 2007), iron-deficient women performed worse on cognitive tasks at the start. After 16 weeks, gains in ferritin (iron stores) were linked to better accuracy, and gains in hemoglobin to faster task completion.

Vegetarians and vegans face extra risk: iron absorption has been estimated at about 14-18% from mixed diets but 5-12% from vegetarian diets (Hurrell & Egli 2010). Vitamin C with plant iron (lemon on lentils, peppers with beans) improves absorption.

Fatigue, poor concentration and irritability from low iron are easy to blame on exam stress. If you have persistent symptoms, ask your doctor for a ferritin test. In a randomized trial of 144 non-anemic women with unexplained fatigue (Verdon 2003), iron supplements reduced fatigue more than placebo. The benefit was only in women with ferritin of 50 micrograms per liter or less. Don’t take iron supplements without a confirmed deficiency: excess iron can be harmful, and supplements should be kept away from young children, for whom iron overdose is dangerous.

B12 deficiency is a risk for vegans. Routine vitamin D testing is not recommended for healthy young adults.

Eating well on a student budget

Energy drinks, takeaway and packaged snacks often cost more per nutrient than whole foods. An energy drink costs about the same as a dozen eggs.

  • Batch cooking: Spend 60 to 90 minutes once a week on brown rice or quinoa (keeps 4 to 5 days in the fridge), lentils or bean soup and chopped vegetables. A dozen hard-boiled eggs keep 5 to 7 days.
  • No-cook meals: Overnight oats with nuts and fruit, canned sardines or tuna on whole-grain crackers, or nut butter on whole-grain bread with a banana.
  • Grocery list: Rolled oats, canned lentils and chickpeas, canned sardines or tuna, eggs, frozen spinach, bananas, mixed nuts, whole-grain bread, peanut butter, frozen blueberries, Greek yogurt and brown rice.

Exam day

The weeks of study matter more than exam-day food. On the day, the goal is to avoid mistakes.

The meal: Eat something familiar two to three hours before: 20 to 30 grams of protein, complex carbohydrates for sustained glucose delivery, and some fat. Around 400 to 600 calories avoids feeling heavy, though this hasn’t been tested as an exam intervention. Good options are a two-egg omelet with toast and fruit, oatmeal with nuts and banana, or toast with peanut butter and yogurt. Avoid sugary cereal, pastries, energy drinks, fried food and skipping the meal.

During the exam: For exams over two hours, a few nuts, a piece of dark chocolate or dried apricots (where rules allow) may help if you get hungry. Bring water.

Caffeine: If you normally drink it, have your usual 100 to 200 mg 30 to 60 minutes before. Don’t double it; that’s more likely to bring anxiety than sharpness. If you don’t normally drink caffeine, exam day is not the day to start.

If you pull an all-nighter

All-nighters are likely to backfire. A review by Stickgold (2005) describes memory consolidation as an active process during sleep, and missing sleep after learning impairs later memory.

If you stay up anyway, eat small protein-rich snacks every two to three hours rather than large meals or sugar. Caffeine restores alertness, but not every kind of thinking. Killgore (2012) kept 54 healthy adults awake for two nights. A 600 mg dose of caffeine reduced sleepiness and improved vigilance, yet decision-making on a gambling task stayed impaired until people slept. Smaller, spaced doses are a better approach, within about 400 mg a day.

Stop caffeine at least four hours before any planned sleep, even a short nap. In one study, a 60-90 minute nap improved a visual learning task as much as a full night of sleep (Mednick 2003). See sleep and diet for food habits that help sleep.

Frequently asked questions

Are brain supplements worth it for exams?

For most students, fixing a confirmed deficiency (such as iron or B12) is more likely to help than nootropics. Caffeine with L-theanine improved attention in a small crossover study (Haskell 2008). Any supplement can interact with medicines; ask a doctor or pharmacist first. Beyond that, the evidence for exam boosters in healthy young adults is thin.

What should I eat the night before an exam?

A normal, balanced dinner with protein, complex carbohydrates and vegetables, such as fish with brown rice and vegetables or a lentil curry. Sleep matters more than the meal: avoid alcohol, limit caffeine after early afternoon and eat early enough that digestion doesn’t keep you up.

Does chocolate help with studying?

In a crossover trial of 30 adults (Scholey 2010), cocoa drinks with 520 or 994 mg of flavanols improved a serial-subtraction task. The higher dose also increased errors on another task. A small serving of dark chocolate has much less flavanol than those drinks, and milk chocolate has far less cocoa and far more sugar.

Can a vegetarian or vegan diet support exam performance?

Yes, with attention to a few nutrients. Watch iron (paired with vitamin C), B12 (supplements are essential for vegans) and DHA (algae supplement). Also watch choline (soy, quinoa and broccoli, though less than eggs) and zinc (legumes, nuts, seeds, whole grains).

Sources

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  • Benton, D. (2011). Dehydration influences mood and cognition: a plausible hypothesis? Nutrients, 3(5), 555-573. doi:10.3390/nu3050555
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  • Clark, I., & Landolt, H. P. (2017). Coffee, caffeine, and sleep: a systematic review of epidemiological studies and randomized controlled trials. Sleep Medicine Reviews, 31, 70-78. doi:10.1016/j.smrv.2016.01.006
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  • Ganio, M. S., Armstrong, L. E., Casa, D. J., McDermott, B. P., Lee, E. C., Yamamoto, L. M., et al. (2011). Mild dehydration impairs cognitive performance and mood of men. British Journal of Nutrition, 106(10), 1535-1543. doi:10.1017/S0007114511002005
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