One Kabob Short of Drug Addiction

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Every once in a while, the scientific literature offers up a gift to write about. This study, Meat Consumption During Pregnancy and Substance Misuse Among Adolescent Offspring: Stratification of TCN2 Genetic Variants, is one of those times. Let me jump to their conclusion, 

“This study identifies low meat consumption in the prenatal period as potentially modifiable risk factor for adolescent substance use.”

That’s right if your mother was a vegetarian you are more likely to abuse alcohol, marijuana and even tobacco. How can this be? But not to worry, to say the study is flawed is being restrained. The underlying hypothesis was that:

“Vegetarian dietary patterns are associated with improved health outcomes among adults and, in addition, have strong ethical imperatives including promotion of sustainability, food security and reducing industrialized production of animals. However, avoidance of relatively nutrient dense meats can decrease intakes of cobalamin, iron, omega-3 fatty acids, selenium and zinc, particularly in young women of childbearing age. … Cobalamin is a biochemically essential nutrient available predominantly from meats and shellfish; up to 62% of vegetarians are deficient in this nutrient during pregnancy….  Profound neurodevelopmental abnormalities [are] due to severe cobalamin deficiencies” [1]

The researchers studied a 14,451 patient cohort of a longitudinal study of women. They used a survey of the women's’ eating habits at the 32nd week of their pregnancy to classify them into one of five groups; “’health conscious, traditional, processed, confectionary and vegetarian.” Fifteen years later they surveyed the offspring of those pregnancies about their substance abuse. Leaving aside the issue of survey accuracy, only 5,246 (36%) of the children participated in the substance abuse survey. We have no information about the eating habits of the remaining 64% of women or the substance abuse habits of their children to use for comparison, but, as you will see, it doesn't really matter.

The researchers also considered other sociodemographic variables housing, highest maternal education, parity, social class, occupations, ethnicity, home overcrowding, maternal age at delivery, disposable income, housing benefits, and measurements of parent-child relationships. These don't matter either, so let's just ignore them as well. They did a number of regressions to find the diets most strongly associated with subsequent substance abuse. There cannot be a better example of data mining, aka "data dredging."

While there was little evidence of an association between substance abuse and prenatal, traditional, processed or confectionary diets and a moderate association with a ‘healthy’ diet, it was the "strong" evidence of an association between substance abuse and vegetarian diets that were now the researcher's focus.

Consider first the children, evidently a group of “party animals.”

  • 50.8% had heavy, frequent or regular binge drinking with 35.2% demonstrating addictive or problematic behavior
  • 29.1% used cannabis with 3.8% having problematic use
  • 10.3% used tobacco weekly

It is probably worth noting that addictive/problematic behavior was much higher for alcohol use (69%) than cannabis (13%) although this is not a brief for cannabis use.

Because the authors' hypothesis concerned cobalamin (Vitamin B12) and other nutritional deficient in this diet, they looked at TNC2, a gene that codes for the transport protein for B12, Cobalamin should be adequately transported when the gene is intact and carried to a lesser degree when it is not. The researchers had data to characterize the TNC2 status of their mothers and found that for homozygous mothers, with intact cobalamin transport, there was a linear “dose-response” relationship between eating meat and lower rates of substance abuse.

That is, cobalamin in meat was good for the offspring. On the other hand, among mothers heterozygous for TNC2 with impaired cobalamin transport, there was no association between meat intake and avoidance of substance abuse. In the face of impaired transport, increased cobalamin from meat was ineffective. The authors stated that the “Risks attributable to cobalamin deficits during pregnancy for adverse adolescent alcohol, cannabis, and tobacco use were 14 %, 37%, and 23% respectively.” What makes this statement so extraordinarily bad is that they never measured cobalamin levels in the mothers or their offspring. There is no evidence for their belief that these children or their mothers were cobalamin deficient. They imputed a deficiency, which is a way of saying they assumed one.

But vegetarians need not worry:

“In identifying vitamin B12 insufficiencies as highly likely to have a contributing role to our findings, greater meat consumption need not be advised to modify this risk. For example, fortification of foods with vegetarian sources of cobalamin and more widespread use of supplements may be low cost and readily feasible interventions.”

I am confused at least a little. I can certainly understand how vegetarian mothers with an intact cobalamin transport system would benefit from supplemental Vitamin B12. But what about those other vegetarian mothers, or for that matter, any mothers without intact cobalamin transport supplements are not going to help them?

To my mind, the overwhelming flaw of this study (and there are plenty) is that the other sociodemographic factors were not considered and their impact upon substance abuse not put into context compared with possible Vitamin B12 deficiencies. There were other factors, lower income, lower educational levels, overcrowded housing that all are known contributors to substance abuse. And let us not leave out the factors that had far more impact than the mother’s diet, measures of the relationship between the parent and the child.

The greater the parental monitoring, parental child arguing and children hiding their activities were all associated with substance abuse in more significant degrees than any of the diet correlates. For example, the odds ratio that a vegetarian mother was associated with problematic cannabis use was 1.36, for parental monitoring 2.20 and children and parents fighting 1.55. And while no clear-cut pattern relating parenting to diet was identified, concerning monitoring and parental-child conflict, vegetarian mom’s were the worst, and concerning the children hiding their activities, only mothers eating processed foods were worse. 

The authors have some a striking conclusion.

“Lower prenatal meat consumption was associated with increased risks of adolescent substance misuse. Interactions between TCN2 variant status and meat intake implicate cobalamin deficiencies”

But there is one last caveat, while their imputed belief that cobalamin deficiencies result from heterozygous TNC2 changes

“may be plausible … there is no consensus in the literature regarding the differences in biological activities of the transcobalamin products of TCN2 homodimers compared to those of TCN2 heterodimers and that this interpretation is therefore speculative.”

We are left with only the association between lower maternal meat consumption and an increased risk of substance abuse. An association with no known causal link. Ridiculous. Given the speculation and grotesque data mining of this study it should not have been sponsored, in part, by our National Institute of Health’s National Institute on Alcohol Abuse and Alcoholism, but by our now defunct Bureau of Mines.


[1] It is probably worthwhile to note the moral imperative of vegetarian diet patterns, it is not simply a choice for health, but a choice for good. Evidently, meat eating is both unhealthy and morally challenged.