Charles Darwin, in his autobiography described
“the oddest case which I have known. A gentleman (who, as I afterwards heard, is a good local botanist) wrote to me from the Eastern counties that the seed or beans of the common field-bean had this year everywhere grown on the wrong side of the pod. I wrote back, asking for further information, as I did not understand what was meant; but I did not receive any answer for a very long time. I then saw in two newspapers, one published in Kent and the other in Yorkshire, paragraphs stating that it was a most remarkable fact that ‘the beans this year had all grown on the wrong side.’ So I thought there must be some foundation for so general a statement.”
I had read this passage a while ago but it suddenly popped up in my mind on reading the new USDA Dietary Guidelines. The Guidlines have a strong recommendation to choose “nutrient dense” food. Since all the food you ingest contains some kind of macronutrient or micronutrient and having a food dense in one or another would depend on how much you thought was good I could not really understood what was meant. I pretty much forgot about it until I saw in a video from a TV broadcast making the same recommendation suggesting that it was intelligible to the general population. I still couldn’t understand what could be meant. The guidelines say, on page 3, “Energy-dense forms of foods, especially foods high in SoFAS, should be replaced with nutrient-dense forms of vegetables…” SoFAs stands for “solid fats and added sugars.” It would be hard to find two more nutrient dense but different substances. So at least nutrient dense is not calorie dense but it is not obvious what it is. Note added in 2013:when I first posted this, I genuinely did not know that nutrient-dense now means micronutrient-dense but I think the critique of the USDA still stands and for a description of currency of an idea that has no real meaning at all, Darwin’s story is still the best. (And, of course, vitamin deficiencies may be the least of our nutritional problems).
Darwin described how he
“went to my gardener, an old Kentish man, and asked him whether he had heard anything about it, and he answered, ‘Oh, no, sir, it must be a mistake, for the beans grow on the wrong side only on leap-year, and this is not leap-year.’ I then asked him how they grew in common years and how on leap-years, but soon found that he knew absolutely nothing of how they grew at any time, but he stuck to his belief. After a time I heard from my first informant, who, with many apologies, said that he should not have written to me had he not heard the statement from several intelligent farmers; but that he had since spoken again to every one of them, and not one knew in the least what he had himself meant. So that here a belief–if indeed a statement with no definite idea attached to it can be called a belief–had spread over almost the whole of England without any vestige of evidence.”
(In case you think that there is any botanical meaning at all: it is not just the leap-year. It is that there is no right or wrong side of the pod at all). Is it possible that the USDA guidelines, put together by the famous 13 experts have made a recommendation that was completely devoid of meaning? Page 11 says that “A nutrient-dense total diet has multiple health benefits and can be implemented in various ways” but what is nutrient-dense? Although never defined, examples are given on pages 19-20.
• Vegetables, fruits, high-fiber whole grains
• Fat-free or low-fat fluid milk and milk products
• Seafood, lean meat and poultry, eggs, soy products, nuts, seeds, and oils
• Very low in solid fats and added sugars (SoFAS)
• Reduced in sodium
The remarkable thing is that in five out of six, the nutrient density is attained by absence of nutrients: fat-free, low-fat, lean, very-low SoFAS, reduced sodium — and is there anything less dense than skim-milk? Paraphrasing Darwin, then, here is a dietary recommendation –if indeed a statement with no definite idea attached to it can be called a recommendation — will be spread over almost the whole of the country without any vestige of evidence.
Richard David Feinman 