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2016 Lecture Summary

26th Apr 2016 by Tom Brenna (Professor of Human Nutrition, Cornell University)

Nutrition and behaviour: are people and governments buying in?

When talking about nutrition, there are three audiences: regular people, scientists, governments.

Regular people

Regular people have long had the concept of “brain food”. The belief that fish is good for the brain dates back to the discovery of the element phosphorus in 1669, followed in 1719 by the realisation that brains are rich in phosphorus. So is fish, and in the nineteenth century the influential naturalist Louis Agassiz suggested that people should eat fish for this reason. His remarks were popularised by Mark Twain, who in response to a would-be author’s query on the topic, replied:[1]

To Young Author: Yes, Agassiz does recommend authors to eat fish, because the phosphorus in it makes brains. So far you are correct. But I cannot help you to a decision about the amount you need to eat - at least, not with certainty. If the specimen composition you send is about your fair usual average, I should judge that a couple of whales would be all that you want for the present. Not the largest kind, but simply good middling-size whales. Mark Twain, in the Galaxy

Fish is brain food. Fish are high in essential fatty acids such as the omega-3 and omega-6 fatty acids, which help build brain cell membranes and are needed for making new connections between them. Phosphorus is required for these processes and for many others.[2]

Thus the concept of brain-selective nutrients was established. It now, more scientifically, includes fatty acids – like the omega-3s DHA and EPA – and minerals like iron, zinc, iodine, selenium and copper. Here the focus is on DHA, because “As calcium is to the bones, DHA is to the brain”.[3]

Why are brain-selective nutrients so important? Imagine the set of all the scientific problems we face. Which one matters most? Climate change? Population increase? An asteroid striking the Earth? The solutions to all of these need human brains: so the most important problem is surely how to build the most effective brains.

Nature shows us many “runaway organs” which have evolved into a greatly exaggerated form – crabs with giant claws, elephant trunks and so on. Humans, as Professor Michael Crawford (who gave last year’s lecture) has noted, have runaway brains. Brain growth is so prioritised in human development that toddler brains are almost the same size as adults.

Scientists

What is the brain made of? Uniquely among body organs, about 60% of its dry matter is fat rich in omega-3 and omega-6. DHA is especially enriched, suggesting its importance. Unlike other fatty acids, from about 28 weeks of pregnancy it begins to accumulate in the rapidly-growing foetal brain. It keeps rising after birth up to about 18 years of age, after which levels are fairly stable throughout life.[4]

In 2004 a randomised controlled trial examined the development of babies breastfed exclusively until they were 6 months old, and then given baby food either enriched in DHA or not.[5] The scientists measured how well the infants could see – their visual acuity – which reflects their nerve development. Within 3 months the DHA group were doing better, and this continued up to 12 months. The difference was highly significant, striking even to the clinician: equivalent to reading 1.5 lines further down the eye chart.

In a 2014 study the late Sheila Innis and colleagues supplemented pregnant mothers with DHA, or a placebo, and then assessed their toddlers’ linguistic ability at 14 or 18 months. The DHA group understood and produced more words, and were more likely to be in the top quartile for linguistic ability, whereas the placebo-supplemented infants were less likely to excel.[6]

Omega-3s are also important for how adult brains function. A meta-analysis – the highest level of medical evidence if conducted correctly – found that EPA is an effective treatment for depression. Or, as a nutritionist would see it, giving EPA can correct a brain-impairing deficiency (like giving Vitamin C corrects scurvy).

Governments

Governments have only recently caught up with the idea of brain-selective nutrients, and there is still little work in the EU, Australia or New Zealand on official recommendations for brain development. The US, however, has now made some progress.[7] This matters both because governments inform the public and because they directly feed millions of people every day, e.g. in the military. Government guidelines are highly influential; individuals and practitioners pay attention.

In 1977, the US Senate Select Committee Report on Nutrition and Human Needs linked too much dietary fat, sugar and salt to heart disease, cancer, obesity, stroke and other killer diseases – and recommended eating less of them. Since then, mental health issues have been recognised in the guidelines; and seafood was recommended for pregnant and breastfeeding women in 2010, addressing the needs of baby’s brain.

Some critics worry about seafood because of contaminants like mercury. However, a meticulously researched and reviewed official report by the U.S. Food and Drug Administration (FDA) found that children’s IQ rises when mothers eat more fish: at 50g/day consumption of salmon in pregnancy, baby has a 3-point higher IQ. Even eating that amount of shark, which is potentially much higher in mercury, still leads to a 2-point IQ increase.[8] Data from the Avon Longitudinal Study of Parents and Children found no evidence of adverse associations between maternal prenatal blood mercury and child development between 6 and 42 months of age.[9]

But it is not just the developing brain that benefits from essential fatty acids. The 2015 Dietary Guidelines for Americans were the first to consider whether diet could help with depression, and with age-related cognitive impairment and decline. Both are huge problems. Dementia and age-related cognitive impairment cost the US over $200 billion, while a nationwide survey (NHANES) estimated that 21 million Americans had experienced debilitating depression. The guidelines concluded that limited evidence supported the conclusion that certain dietary patterns do lead to lower rates of development of depression and impairment. These diets involve seafood with DHA, more vegetables, whole fruits, whole grains and nuts and at the same time eating less red meat, salt and sugar.

Wild vs. Farmed

Some methods of food production pose a challenge to the nutritional quality of the food supply. The conventional wisdom is that wild fish is higher in essential nutrients than farmed fish. But for salmon and trout (in the US and UK at least), properly farmed animals can have as much omega-3 as wild fish. Other farm species can also, through correct feeding and aquaculture, be very useful sources of essential fatty acids.

The Dietary Guidelines Advisory Committee report now recommends that farmed fish should have the same levels of nutrients as wild fish of the same species – a principle which should be extended to other food production.

Conclusions

Government is slowly buying in to the idea that diet matters for brain health and development, issuing guidelines for pregnancy, breastfeeding and infancy. Research is increasing rapidly: there have been numerous studies on depression and diet in the last two years but while interest is growing, the application of the principles is not yet widespread.

So where does that leave us? While it is clear that the structures of the brain are laid down in the earliest stages of life, there is ample evidence that nutritional intervention is essential throughout the life-cycle. If you build a house, you maintain it to keep it sound. The same goes for our brains.

Endnotes

[1] Twain is quoted in the Montreal Daily Witness, 16 February 1871, available from Google. It is said that his remarks led to higher demand for fish in New York.
[2] Western diets contain much more phosphorus than they used to, so taking it as phosphate supplements is not recommended by, for example, the Royal Society of Chemistry..
[3] The quotation is from the high-profile US paediatrician William Sears’ book The Omega-3 Effect (Little, Brown and Co., 2012).
[4] Carver, J. D., V. J. Benford, et al. (2001) “The relationship between age and the fatty acid composition of cerebral cortex and erythrocytes in human subjects.” Brain Research Bulletin 56(2): 79-85.
[5] Hoffman, D. R., R. C. Theuer, et al. (2004)). “Maturation of visual acuity is accelerated in breast-fed term infants fed baby food containing DHA-enriched egg yolk.” The Journal of Nutrition 134(9): 2307-2313.
[6] Mulder, K. A., D. J. King, et al. (2014). “Omega-3 fatty acid deficiency in infants before birth identified using a randomized trial of maternal DHA supplementation in pregnancy.” PLoS ONE 9(1): e83764.
[7] Tom Brenna was on the US government committee which established the scientific basis for the 2015-2020 guidelines.
[8] A Quantitative Assessment of the net effects on Fetal Neurodevelopment from eating commercial fish (As Measured by IQ and also by Early Age  Verbal Development in Children) (May 2014)
[9] Golding, J., S. Gregory, et al. (2016). “Associations between prenatal mercury exposure and early child development in the ALSPAC study.” Neurotoxicology 53: 215-222.

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