I struggled today with balancing the oats and maltodextrin mixture of my Soylent. The reason is that grains like oats have quite a bit of Manganese. With 100g of oats (a very reasonable amount per day), this accounts for about 5mg. Combine with a multivitamin, adding another 5mg, and I was now teetering over the edge of the upper limit listed by Soylent (later edit: this was a mistake; the figure is from the USDA, but for us DIYers, we commonly associate the two)
At this point, I wondered, how, exactly are they coming up with this 11mg/day figure.
Here is what I realized:
Maganese toxicity from foods has not been reported in humans. (a more rigorous reference to come).
So how are they getting that figure of 11mg/day? See the article here by Greger (you may need an academic proxy):
One reason for the difficulty in recommending optimal intakes of manganese is that scientists really are not sure of typical manganese intakes. Daily food composites prepared on the basis of the FDA’s Total Diet Study menus contained on average 2.2 mg Mn for women and 2.7 mg Mn for men (Pennington et al. 1989). The average intakes of adults eating Western-type and vegetarian diets in various surveys ranged from 0.7 to 10.9 mg Mn/d (Freeland-Graves 1994, Gibson 1994).
- A more detailed summary of this is given in this article by Ljung and Vahter (apologies for the length). Note that NOAEL refers to “no observed adverse effect level”. Amusingly, I want you to notice that the guy who’s study is used to determine the 11mg/day limit was the same guy above who said “scientists really are not sure…”
How the NOAEL for manganese was established
In the background document for the WHO drinking-water guidelines (WHO 2004), the use of 11 mg as a NOAEL is based on a review by Greger (1999) and on a report on dietary reference values for manganese published by the Institute of Medicine in 2000 (IOM 2001):
A review of typical Western and vegetarian diets found average adult manganese intakes ranging from 0.7 to 10.9 mg/day (Greger 1999; Institute of Medicine [IOM] 2002 [sic]). The upper range manganese intake value of 11 mg/day from dietary studies is considered a NOAEL. It is not believed that this amount of manganese in the diet represents an overexposure to the element (IOM 2002 [sic]). (WHO 2004)
The IOM in turn, also refers to Greger (1999):
A NOAEL of 11 mg/day of manganese from food was identified based on the data presented by Greger (1999). Greger (1999) reviewed information indicating that people eating Western-type and vegetarian diets may have intakes as high as 10.9 mg/day of manganese [. . . .] Because no adverse effects due to manganese intake have been noted, at least in people consuming Western diets, 11 mg/day is a reasonable NOAEL from food. (IOM 2001)
However, the article by Greger (1999) did not focus on manganese intake from different diets but rather on potential biomarkers of manganese in human nutrition and toxicology. In the introduction section on manganese exposure she stated that “the average intakes of adults eating Western-type and vegetarian diets in various surveys ranged from 0.7–10.9 mg Mn/day,” with reference to Gibson (1994) and Freeland-Graves (1994). However, no mention of these values is made in Gibson (1994), whose article is a review on trace elements in vegetarian and omnivorous diets, with a concern for deficiencies in vegetarian diets. The Freeland-Graves (1994) article is also a review published in a book on risk assessment of essential elements by the International Life Sciences Institute. The intake values of 0.7–10.8 mg Mn/day were observed for Canadian women in a study carried out by Gibson and Scythes in 1982. These values were also cited in the Freeland-Graves (1994) review and presented in a table of daily manganese intakes compiled from several studies.
The values used for setting the NOAEL thus originate from one study, where 100 Canadian women aged 30 ± 6.1 years were asked to complete dietary protocols of all consumed foods and beverages (including drinking water) in their own homes for 3 consecutive weekdays (Gibson and Scythes 1982). The authors present both calculated and analyzed intake values. The calculated daily manganese intake ranged from 0.7 to 10.8 mg, where 90% of the women ingested < 5 mg/day, and almost half the women (40%) ingested < 2.5 mg/day. The average daily manganese intake was calculated at 3.1 ± 1.5 mg. The analyzed manganese intake from duplicate portions provided a slightly lower average daily manganese intake of 2.4 mg/day. The analyzed maximum intake was not presented. The slight discrepancy between the calculated and the analyzed manganese intakes was explained by the authors to be a result of an overestimation in portion size (Gibson and Scythes 1982).
The NOAEL of 11 mg/day thus is based on calculated daily intakes of manganese and not on actual measurements of manganese intakes. No mention is made of the subjects’ health statuses or why it seems unfounded to draw any conclusions on a “no observed adverse effect level” of daily manganese intakes at 11 mg. In fact, several studies from different countries have reported daily manganese intakes after 1982, when the Gibson and Scythes study was published. Table 1 shows manganese intake data from an array of countries and ages. Children’s average manganese intake from omnivorous diets was reported to be about 2 mg/day (mean values range from 1.3 to 3.6 mg/day), whereas adult omnivorous diets resulted in a slightly higher intake of about 2.7 mg/day (mean range 1.5–3.9 mg/day). This value is similar to the analyzed intake value of 2.4 mg/day reported by Gibson and Scythes (1982). Both children and adults with a vegetarian diet have reportedly higher values of daily manganese intake than those with an omnivorous diet, which can be explained by the higher manganese concentration in plants than in meat and fish. The daily intake also seems to differ with country of residence, likely because of differing diets. None of the studies found intakes as high as 11 mg/day.
I have bolded some of the text.
I realize this was a bit long, so let me summarize for you what this indicates: the figure of 11mg/day was based on a single survey of 30-year old Canadian women in which they approximated how much Maganese was consumed in an average diet. These figures ranged from 0.7-10.9mg/day. Based on the fact that these people were “healthy”, they concluded that 11mg should be the recommended upper limit.
What this means is that if you are a Canadian woman who consumes 0.7-10.9mg of Manganese per day, then you should be fine. What is the upper limit of Manganese for other people? Is 15mg/day okay? Is 20mg/day okay? We have no freakin’ idea.
My warning to all of you DIY Soylenters is to understand that there is a lot we don’t understand about diet and recommendations, and the more you dig into these recommendations, the more questions you find. This is why, as a scientist, Rob’s blog post struck me the wrong way:
Epistemic arrogance – Elemental analysis has given us a finite, complete list of the elements our bodies are made of. This doesn’t tell us the different chemical configurations required, such as vitamins, but patients have lived for many years on synthetic diets in a medical setting. It was premature in the 19th century, but it’s overdue today. Again, beware of zero-risk bias. How nutritionally complete is the average western diet already?
There is a sense of epistemic arrogance in following certain food intake guidelines that you’ve come to realize are based on singular studies and very limited data. How many other ‘recommended intakes’ are based on limited data and somewhat sketchy conclusions? I personally like the idea of Soylent, but just be careful.
And as for the Manganese issue? Now that I understand where this 11mg figure is coming from, I’m not going to freak out if I exceed this value.