Did rationing in World War 2 increase intelligence of Britons?

The journal article is Aging trajectories of fluid intelligence in late life: The influence of age, practice and childhood IQ on Raven's Progressive Matrices and the key passage is reproduced below:

"Standardizing the MHT [original] scores indicated a difference between the cohorts of 3.7 points. This is slightly smaller than expected and may be brought about by survival and selection bias discussed above. Late life comparisons indicate a significantly greater difference between the cohorts, comparing the cohorts at age 77; where there is overlap in data we find a difference of 10.4 raw RPM points or 16.5 IQ points, which is surprisingly large."

What this says is that both groups started out pretty much the same but by the time they had got into their 70s the younger group was much brighter.  The authors below attribute the difference to nutrition, which is pretty nonsensical.  They say that eating "rich, sugary and fatty foods" lowers IQ but where is the evidence for that?  The only studies I know are epidemiological and overlook important third factors such as social class. So those studies can only be relied on if you believe that correlation is causation, which it is not.  And one might note that average IQs in Western nations have been RISING even as consumption of fast food has been rising.  So even the epidemiology is not very supportive of the claims below.

Where important  micronutrients (iodine and iron particularly) are largely absent in the food of a population  -- as in Africa -- nutritional improvements can make a big difference but the idea that Aberdonians in the 1920s were severely deprived of such micronutrients seems fanciful. Aberdeen has long been an important  fishing port and fish are a major source of iodine -- and iron is mostly got from beef and Scots have long raised and eaten a lot of beef.  The traditional diet of poor Scots -- "mince 'n tatties" -- is certainly humble but it does include beef. Aberdeen even has an important  beef animal originating there: The widely praised "Aberdeen Angus".  You can eat meat from them in most of McDonald's restaurants these days.

So why was the IQ divergence between the two groups below not observed in early childhood when it was so strong in later life?  A divergence of that kind (though not of that magnitude) is not unprecedented for a number of reasons:  IQ measurement at age 11 is less reliable than measures taken in adulthood; IQ becomes more and more a function of genetics as we get older.  In early life environmental factors have more impact and it takes a while for (say) a handicapping early environment to be overcome. 

But I suspect that the main influence on the finding was that two different tests were used.  IQ was measured at age 11 by an educational aptitude test and in the 70s it was measured by a non-verbal test.  The two were correlated but only about .75, which does allow for considerable divergence.  So the oldsters (1921 cohort) were simply not good at non-verbal puzzles, probably because they had little experience with them.  The tests they did in 1921, however mostly used problems similar to problems they had already encountered many times in the course of their schooling.

The 1936 cohort, by contrast, had most of their education in the postwar era when people spent longer in the educational system. And IQ testing in the schools was much in vogue up until the 1960s so that generation would have had a much wider testing experience.

The retest was, in other words, invalid.  It was not comparing like with like

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A study by the University of Aberdeen and NHS Grampian has found that children who grew up during the Second World War became far more intelligent than those who were born just 15 years before.

Researchers think that cutting rich, sugary and fatty foods out of the diets of growing children had a hugely beneficial impact on their growing brains.

The University of Aberdeen team examined two groups of people raised in Aberdeen, one born in 1921 and one born in 1936. These people are known as the Aberdeen Birth Cohort and were tested when they were aged 11 and when they were adults after the age of 62. The study consisted of 751 people all tested aged 11 and who were retested between 1998 and 2011 on up to five occasions.

Researchers compared the two groups at age 11 found an increase in IQ of 3.7 points which was marginally below what was expected but within the range seen in other studies. However, comparison in late life found an increase in IQ of 16.5 points which is over three times what was expected.

Before the war, more than two thirds of British food was imported. But enemy ships targeting merchant vessels prevented fruit, sugar, cereals and meat from reaching the UK.

The Ministry of Food issued ration books and rationing for bacon, butter and sugar began in January 1940.

But it was the MoF’s Dig For Victory campaign, encouraging self-sufficiency, which really changed how Britain ate. Allotment [mini  farm] numbers rose from 815,000 to 1.4 million.

Pigs, chickens and rabbits were reared domestically for meat, whilst vegetables were grown anywhere that could be cultivated. By 1940 wasting food was a criminal offence.

More HERE