Short answer: Your brain needs enough protein, not a lot. In small studies, protein-rich or balanced meals led to better memory and reaction times later in the morning than carbohydrate-rich meals. Very high intakes show no benefit. Expert groups suggest 1.0 to 1.2 g per kg a day for healthy older adults, spread across meals. With kidney disease, ask your doctor.

A diet with enough protein, spread across meals, supports the brain, but a high-protein diet has no proven extra benefit. The evidence is preliminary: small meal studies show short-term effects on memory and reaction time. High-protein meals also reduce the amount of tryptophan, the serotonin building block, that reaches the brain.

How much protein, and when

  1. Get enough. The RDA for adults is 0.8 g per kilogram of body weight a day. Expert groups recommend 1.0 to 1.2 g/kg for healthy older adults. If you have kidney disease, ask your doctor what is right for you.
  2. Spread it across meals. About 25 to 35 grams per meal is a common target, rather than little at breakfast and a lot at dinner.
  3. Include protein at breakfast. Eggs, Greek yogurt, cottage cheese or a protein smoothie. Small studies suggest protein-containing or balanced breakfasts may support late-morning performance better than carbohydrate-only ones.
  4. Add complex carbohydrates at dinner. Whole grains, sweet potatoes or legumes alongside moderate protein may favor serotonin and help you fall asleep.
  5. Mix your sources. Fish such as salmon and sardines for omega-3s, eggs for choline, legumes for fiber and polyphenols, dairy or soy, and poultry or lean meat in moderation.
  6. Don’t chase very high intakes. There’s no evidence they improve thinking, and they can crowd out other foods.

How protein becomes brain chemicals

The brain makes its main signaling chemicals from amino acids in food:

  • Tyrosine becomes dopamine and norepinephrine, which drive motivation, alertness and focus. The process needs iron, tetrahydrobiopterin, vitamin B6 and vitamin C; see our guide to B vitamins and the brain.
  • Tryptophan becomes serotonin, which helps regulate mood, sleep and impulse control. Tryptophan is essential: the body can’t make it.
  • Glutamate, the brain’s main “go” signal, comes from glutamic acid in protein, and is turned into GABA, the main “stop” signal, with help from vitamin B6.
  • Histidine becomes histamine, which supports wakefulness and attention.

A review by Fernstrom and Fernstrom (2007) describes how eating more protein raises brain tyrosine and stimulates dopamine and norepinephrine production in active neurons, based mainly on animal studies. Read more in dopamine and diet.

Tyrosine matters most under stress or heavy mental load. At rest, the key enzyme is tightly regulated and extra tyrosine has little effect. A review of supplement studies (Jongkees 2015) found that results vary, but concluded that tyrosine seems to help in short-term stressful or demanding situations. Whether a protein-rich meal does the same hasn’t been tested directly.

The tryptophan paradox

High-protein meals reduce the amount of tryptophan reaching the brain. Tryptophan shares a transporter into the brain with five other amino acids (tyrosine, phenylalanine, leucine, isoleucine and valine). How much gets in depends on its ratio to these competitors, not on its absolute level.

Tryptophan is the least abundant amino acid in nearly all dietary proteins. A high-protein meal raises the competitors more than tryptophan, so the ratio falls. In a small study (Wurtman 2003), the plasma tryptophan ratio was lower after a protein-rich breakfast than after a carbohydrate-rich one. In the 8 people who ate both, the median difference was 54%.

Carbohydrates do the opposite. The insulin they trigger moves leucine, isoleucine and valine into muscle, while tryptophan, mostly bound to a blood protein, is less affected. The ratio rises and more tryptophan reaches the brain. This is the biochemical explanation offered for why carbohydrate-rich meals can feel calming and protein-rich meals more alerting. The idea that carbohydrate cravings reflect low serotonin is a hypothesis.

This doesn’t mean high-protein diets cause serotonin deficiency. The brain has ways to compensate. But meal composition affects the balance of brain chemicals for a few hours after eating. Over time, a diet very high in protein with few carbohydrates may subtly favor dopamine over serotonin. A meal with both protein and complex carbohydrates supports both.

Protein, blood sugar and morning performance

Adding protein to a meal tends to blunt the rise in blood sugar. Gannon (2003) studied 12 people with untreated type 2 diabetes. Five weeks on a diet with 30% of energy from protein instead of 15% reduced the 24-hour glucose response by 40% and lowered HbA1c. In young adults (Benton 2003), people remembered more in the late morning after a low-GI breakfast than a high-GI one, though performance tracked blood glucose only loosely. So toast with eggs may give a steadier morning than toast and jam, though the cognitive studies are not consistent. See blood sugar and brain function.

In a crossover study of 15 male students (Fischer 2002), a protein-rich meal gave the best short-term memory accuracy and a balanced meal the fastest reaction times. A carbohydrate-rich meal helped attention only in the first hour, after which the balanced and protein-rich meals did better. A review of adult breakfast studies (Galioto & Spitznagel 2016) found a small but consistent memory advantage from eating breakfast. There were too few studies of breakfast composition to draw firm conclusions. Our breakfast and cognition article covers this in more detail.

Evening carbohydrates and sleep

In 12 healthy young men (Afaghi 2007), a high-GI carbohydrate meal four hours before bed shortened the time to fall asleep compared with a low-GI meal. No high-protein meal was tested. The proposed reason is the tryptophan effect above. This doesn’t mean white rice for dinner. A balanced evening meal with complex carbohydrates and moderate protein may suit sleep better than a purely high-protein dinner.

Spreading protein through the day

In eight healthy adults (Mamerow 2014), spreading protein evenly across three meals (about 30 grams each) gave 25% more muscle protein synthesis over 24 hours than a skewed pattern. The skewed pattern was 10 grams at breakfast, 15 at lunch and 65 at dinner, typical of many Western adults. The study measured muscle, not the brain; whether the same applies to the brain is not known.

Protein needs at different ages

Children: The developing brain needs amino acids to build its structures. Undernutrition in early childhood, shown by stunting, is linked to poorer cognitive development and school achievement in long-term studies from developing countries (Grantham-McGregor 2007). The RDA for children is 0.95 to 1.05 g/kg a day.

Older adults: Aging muscles respond less to protein. Roberts (2012) followed 937 cognitively normal older adults in the Mayo Clinic Study of Aging for about four years. A higher share of energy from protein was linked to lower risk of mild cognitive impairment or dementia. The trend was statistically significant (p for trend 0.03), but the top-versus-bottom quarter comparison was not, and the study is observational. Expert groups recommend 1.0 to 1.2 g/kg a day for older adults, mainly for muscle and function, and up to 1.5 g/kg with acute or chronic illness. People with chronic kidney disease are an exception and should follow their doctor’s advice. See our over-50 brain diet.

Pregnancy: The recommended intake is about 1.1 g/kg a day, rising in the second and third trimesters.

Animal or plant protein?

Animal proteins (meat, fish, eggs, dairy) contain all nine essential amino acids and are highly digestible. They also bring nutrients that are hard to get from plants. These include vitamin B12, ready-made DHA and EPA from fatty fish, well-absorbed heme iron, choline (especially in eggs and liver) and creatine.

Plant proteins (legumes, soy, nuts, seeds, whole grains) are each short in one or more essential amino acids, but combining them through the day fills the gaps. Soy is a complete protein. Plant sources bring more fiber and polyphenols.

If you eat a plant-based diet, combine protein sources, take vitamin B12 and watch iron, zinc, choline and omega-3. Some vegetarians consider creatine. In a crossover trial of 45 young vegetarians (Rae 2003), 5 g a day for six weeks improved working memory and reasoning scores. Ask a doctor first if you have kidney disease or take medication.

Can you eat too much protein?

More protein doesn’t mean more brain chemicals. The enzymes that make dopamine and serotonin are self-limiting, and once there’s enough raw material, extra does little. The Jongkees review concluded that tyrosine helps only when demand temporarily depletes dopamine and norepinephrine. There is no evidence that 2.5 or 3.0 g/kg a day, common among bodybuilders, gives any cognitive advantage.

  • Kidneys: In chronic kidney disease, high protein can speed the decline in kidney function, so individual medical advice is needed. A meta-analysis of 28 trials (Devries 2018) found higher-protein diets did not change kidney function in healthy adults, but evidence for very high intakes over many years is limited.
  • Crowding out other foods: Very high-protein diets can displace fruit, vegetables, whole grains and legumes.
  • Gut and heart: High protein with little fiber increases protein fermentation in the colon; whether this matters for the brain is unknown. Red meat raises TMAO, a gut-bacteria product linked to cardiovascular risk in epidemiological studies (Wang 2011). Whether it causes harm is not settled, but it’s another reason to vary your protein.

Frequently asked questions

Can high-protein diets cause depression by lowering serotonin?

The risk is modest for people eating balanced diets, because the serotonin system can compensate. Problems are more likely with extreme high-protein, very low-carbohydrate diets kept up for long periods. Including complex carbohydrates avoids keeping the tryptophan ratio low. If you have depression, diet is not a substitute for the treatment your doctor prescribes.

Is whey protein good for the brain?

Whey is a complete, fast-absorbed protein, and its alpha-lactalbumin fraction is unusually rich in tryptophan. In 58 adults (Markus 2000), an alpha-lactalbumin-enriched diet raised the plasma tryptophan ratio by 48% compared with casein. In stress-prone participants it reduced cortisol and depressive feelings under experimental stress. For most people, whey is a convenient protein source with no special advantage over whole foods.

Does protein intake affect Alzheimer’s risk?

In the Mayo Clinic study above, a higher share of energy from protein was linked to lower risk, but this is observational. The Mediterranean and MIND diets, which favor fish and plant protein over red meat, are linked to lower Alzheimer’s risk in observational studies.

Sources

  • Afaghi, A., O’Connor, H., & Chow, C. M. (2007). High-glycemic-index carbohydrate meals shorten sleep onset. American Journal of Clinical Nutrition, 85(2), 426–430. doi:10.1093/ajcn/85.2.426
  • Benton, D., Ruffin, M. P., Lassel, T., Nabb, S., Messaoudi, M., Vinoy, S., Desor, D., & Lang, V. (2003). The delivery rate of dietary carbohydrates affects cognitive performance in both rats and humans. Psychopharmacology, 166(1), 86–90. doi:10.1007/s00213-002-1334-5
  • Devries, M. C., Sithamparapillai, A., Brimble, K. S., Banfield, L., Morton, R. W., & Phillips, S. M. (2018). Changes in kidney function do not differ between healthy adults consuming higher- compared with lower- or normal-protein diets: a systematic review and meta-analysis. Journal of Nutrition, 148(11), 1760–1775. doi:10.1093/jn/nxy197
  • Fernstrom, J. D., & Fernstrom, M. H. (2007). Tyrosine, phenylalanine, and catecholamine synthesis and function in the brain. Journal of Nutrition, 137(6 Suppl 1), 1539S–1547S. doi:10.1093/jn/137.6.1539S
  • Fischer, K., Colombani, P. C., Langhans, W., & Wenk, C. (2002). Carbohydrate to protein ratio in food and cognitive performance in the morning. Physiology & Behavior, 75(3), 411–423. doi:10.1016/s0031-9384(01)00676-x
  • Galioto, R., & Spitznagel, M. B. (2016). The effects of breakfast and breakfast composition on cognition in adults. Advances in Nutrition, 7(3), 576S–589S. doi:10.3945/an.115.010231
  • Gannon, M. C., Nuttall, F. Q., Saeed, A., Jordan, K., & Hoover, H. (2003). An increase in dietary protein improves the blood glucose response in persons with type 2 diabetes. American Journal of Clinical Nutrition, 78(4), 734–741. doi:10.1093/ajcn/78.4.734
  • Grantham-McGregor, S., Cheung, Y. B., Cueto, S., Glewwe, P., Richter, L., & Strupp, B. (2007). Developmental potential in the first 5 years for children in developing countries. The Lancet, 369(9555), 60–70. doi:10.1016/S0140-6736(07)60032-4
  • Jongkees, B. J., Hommel, B., Kühn, S., & Colzato, L. S. (2015). Effect of tyrosine supplementation on clinical and healthy populations under stress or cognitive demands — a review. Journal of Psychiatric Research, 70, 50–57. doi:10.1016/j.jpsychires.2015.08.014
  • Mamerow, M. M., Mettler, J. A., English, K. L., Casperson, S. L., Arentson-Lantz, E., Sheffield-Moore, M., Layman, D. K., & Paddon-Jones, D. (2014). Dietary protein distribution positively influences 24-h muscle protein synthesis in healthy adults. Journal of Nutrition, 144(6), 876–880. doi:10.3945/jn.113.185280
  • Markus, C. R., Olivier, B., Panhuysen, G. E., Van der Gugten, J., Alles, M. S., Tuiten, A., et al. (2000). The bovine protein alpha-lactalbumin increases the plasma ratio of tryptophan to the other large neutral amino acids, and in vulnerable subjects raises brain serotonin activity, reduces cortisol concentration, and improves mood under stress. American Journal of Clinical Nutrition, 71(6), 1536–1544. doi:10.1093/ajcn/71.6.1536
  • Rae, C., Digney, A. L., McEwan, S. R., & Bates, T. C. (2003). Oral creatine monohydrate supplementation improves brain performance: a double-blind, placebo-controlled, cross-over trial. Proceedings of the Royal Society B, 270(1529), 2147–2150. doi:10.1098/rspb.2003.2492
  • Roberts, R. O., Roberts, L. A., Geda, Y. E., Cha, R. H., Pankratz, V. S., O’Connor, H. M., Knopman, D. S., & Petersen, R. C. (2012). Relative intake of macronutrients impacts risk of mild cognitive impairment or dementia. Journal of Alzheimer’s Disease, 32(2), 329–339. doi:10.3233/JAD-2012-120862
  • Wang, Z., Klipfell, E., Bennett, B. J., Koeth, R., Levison, B. S., DuGar, B., et al. (2011). Gut flora metabolism of phosphatidylcholine promotes cardiovascular disease. Nature, 472(7341), 57–63. doi:10.1038/nature09922
  • Wurtman, R. J., Wurtman, J. J., Regan, M. M., McDermott, J. M., Tsay, R. H., & Breu, J. J. (2003). Effects of normal meals rich in carbohydrates or proteins on plasma tryptophan and tyrosine ratios. American Journal of Clinical Nutrition, 77(1), 128–132. doi:10.1093/ajcn/77.1.128