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expert reaction to study looking at Marmite and brain response to stimuli

Publishing in the Journal of Psychopharmacology scientists investigated whether dietary intervention aimed at increasing levels of the neurotransmitter GABA can influence neural response to basic sensory stimuli.

 

Catherine Collins, Registered Dietitian and Spokesperson for The British Dietetic Association, said:

“From depression to happiness, how food influences mood is a popular topic for investigation in psychology research.  Whilst animal studies can be used to measure brain levels of dietary constituents to estimate effect on mental and cognitive function, invasive sampling techniques don’t lend themselves to general psychology research, and so proxy markers of behaviour and/or brain function are used to justify the effect – or not – of dietary intervention.

“In this study, subjects were advised to take 5g / 1 teaspoon of Marmite or (placebo) smooth peanut butter each day, and steady state EEG monitoring was used to demonstrate differences in the brain response to visual stimuli.  The authors suggest this was consistent with an increase in availability of GABA manufactured from glutamate, a naturally occurring constituent of Marmite, present in much smaller amounts in peanut butter.

“Marmite is a rich source of glutamate, the substance that generates the ‘umami’ taste of ‘savouriness’ in foods we eat.  Analysis by the researchers demonstrated the 5g portion of Marmite provided 140mg of glutamate, and the same weight of peanut butter, 80mg.  Yet no attempt was made to establish baseline intake of glutamate rich, ‘umami’ containing foods within or between groups.  Matured cheeses, and others like Roquefort and Parmesan, and cured meats are all rich in glutamate.  Fish sauces, including Worcestershire sauce, are also rich in glutamate.  Including soy sauce, soy proteins, mushrooms, ripe tomatoes and walnuts in the diet would have all skewed the contribution of glutamate to the diet, and this was not factored in as a confounding variable in their analysis.  A 10ml dash of soy sauce, a sliver of Roquefort, a modest serving of Parmesan on top of a pasta dish, or a couple of tomatoes would have provided more glutamate than the Marmite serving itself, and that did not include lower levels present naturally in dietary protein-rich foods.

“That Marmite had an influence was not in doubt.  However, as a dietitian I’d suggest that it was the addition of over half a gram of salt, around a tenth of the daily recommended amount, that may have had a greater effect through its impact on thirst and hydration, and possibly blood pressure.  Perhaps the pleasure of Marmite-lovers in being able to consume a favourite food daily as part of an experimental study could also have influenced the glutamate-GABA ratio in the brain.  As neither of these physiological responses were measured, it’s hard to venture a conclusion.

“Marmite is a useful food in terms of B group vitamin provision, and as a sugar-free alternative to jam on bread.  But with so little control of baseline diet, and that glutamate and GABA in the brain can be easily converted from one to another, the rationale for differences in EEG readings being related to diet is unconvincing, and I presume the alternative may have been found had participants disliked Marmite.”

 

Prof. David Smith, Professor Emeritus of Pharmacology, University of Oxford, said:

“The observations are clear enough but the interpretation is not sound. The amount of vitamin B12 in the 5 mL helping of Marmite taken each day (1.45 micrograms) is far too little to have any effect on the brain.  The normal dietary intake of B12 is about 2 micrograms per day.  There is also very little experimental evidence that B12 influences GABA in the brain and no theoretical basis for it to do so.  The authors might consider whether folic acid, present in Marmite at levels about 150 times greater than B12 could be the active factor.

“For people that are thinking about increasing their intake of B12, this vitamin is not naturally present in yeast, from which Marmite is made, but is added by the manufacturer.  Folic acid, on the other hand, is naturally enriched in Marmite and the discovery of folic acid was made when Marmite was found to prevent the anaemia of pregnancy by Lucy Wills in 1931.”

 

Dr Martin Coath, Associate Lecturer, Plymouth University, said:

“It is a shame that they stopped at using Marmite because their principle hypothesis is that it is the B vitamins, particularly the B12, in the Marmite that is responsible in some way for the observed effect.  This would have been simple to confirm by repeating the experiment with B12 supplements at the same level as is found in the commercial spread.  This level is, in any case, achieved in the spread by adding supplements.  I would be very interested to see if the results were repeatable with B12 only.

“It is certainly interesting that a significant change can be observed with such a simple, and moderate, dietary modification.  However, there is no suggestion that such a change would be an improvement with respect to any practical task, or clinical condition.  But I am sure that commercial interests that depend on marketing cognitive or health improvements through dietary supplements or modification will seize, and misuse, this result gleefully!”

 

Prof. Dorothy Bishop, Professor of Developmental Neuropsychology, University of Oxford, said:

“On the positive side, the study adopted an experimental approach, with participants randomised to treatment (Marmite or peanut butter).

“However, the sample size is very small.  I would be dubious about accepting the findings without a replication in an independent sample.”

 

Dr James Pickett, Head of Research at Alzheimer’s Society, said:

“Evidence shows that our diet plays an important role in the way our brain functions. This research only looked at how men in their 20s responded to visual stimuli rather than testing their thinking or memory, so there’s no way to say from this study whether eating Marmite can affect your dementia risk.  But the study does give us a deeper understanding of how certain aspects of diet could affect the function of nerve cells in the brain.

“Along with eating a healthy diet, the best ways to reduce your risk of dementia are to exercise regularly, avoid smoking and keep your blood pressure in check.”

 

* ‘Dietary modulation of cortical excitation and inhibition’ by Anika K. Smith et al. published in the Journal of Psychopharmacology on Wednesday 5 April 2017.

 

Declared interests

Catherine Collins: “Hate Marmite. Introduced Marmite to daughter as toddler. She loves Marmite.”

Prof. David Smith: “I have no conflicts.”

Dr Martin Coath: “I have no interests.”

None others received.

 

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