I came across a study from 2008 that has found that many children categorized as obese are getting too few calories and too little of four different micronutrients. This article at VitalChild has a good summary:
Researchers have long blamed childhood obesity and diabetes, especially in poor neighborhoods, on too much food and too little exercise.
But new findings from a San Antonio study point to another explanation: children living in poverty are obese in part because they don’t eat enough to meet the daily nutritional requirements needed for cell function and metabolism.
A 9-year-old should consume 1,400 to 2,200 calories daily to sustain their growth, said Dr. Roberto Trevino, director of the Social and Health Research Center, a nonprofit organization. But in the study of 1,400 inner-city children, 44 percent were consuming less than 1,400 calories, and 33 percent were obese.
“They were not overeating,” Trevino said. “This study shows these kids were not eating enough, and when they did eat it was all the wrong things.”
Missing from the children’s diets were four key nutrients: calcium, magnesium, potassium and phosphorus. All play important roles, but magnesium is involved in more than 300 enzymatic reactions in the body that help to spur metabolism and cell function.
When magnesium–found in cooked spinach, black beans, bran cereal and other foods–is missing from the diet, it can predispose an individual to diabetes, Trevino said.
I wonder how much of the recent uptick in Type 2 diabetes in children is caused by a lack of magnesium? Something to add to the “correlation does not equal causation” files: here we have an example of a third factor (lack of magnesium) contributing to both diabetes and high BMI.
At the bottom of the article, they list examples of foods high in each of the four micronutrients that the children in the study were lacking. The foods chosen for potassium were interesting:
• Potassium: Sweet potato, tuna, bananas, spinach, peaches
One food that is known for being high in potassium is conspicuously absent from this list: potatoes. I did a quick search for “potassium potatoes”, and the first page of this slideshow says, “The big surprise is that bananas don’t even make the top 10 list of superfoods with the most potassium!” But bananas made the VitalChild list even though they’re lower in potassium than potatoes. I’m assuming that this is because potatoes have been linked to obesity and the “obesity epidemic”–Walter Willett and the Harvard School of Public Health are big promoters of this idea.
The slideshow features potatoes at slide #5.
Potatoes: It’s America’s favorite vegetable, and one potato has 610 mg of potassium and 145 calories – if you eat the skin.
Even per calorie rather than per weight/volume (and remember, the kids in this study weren’t getting enough calories*), the potatoes (with skin on) have more potassium than tuna, bananas, or peaches.
(Sweet potatoes do have a lot of potassium, though. From the slideshow: Sweet potatoes: This root vegetable is the top source of potassium – one potato has 694 mg of potassium – about 15% of the daily recommended amount – and just 131 calories.)
The paleo fad hasn’t helped the potato’s reputation. The paleo people seem to be pushing the “carbs=bad” line hard, but we did eat root vegetables in the hunter-gatherer days; they were mostly gathered by older women.
From Sarah Hrdy’s Mothers and Others (because you know I can’t resist an opportunity to quote Sarah Hrdy):
“[Anthropologists] O’Connell and colleagues propose that long-term trends toward a cooler, drier climate at the end of the Pliocene pressured the precursors of Homo erectus to seek new ways to supplement their primary diet of fruit. By around two million years ago, game was increasingly important, but its availability was unpredictable. A division of labor between men who hunted and women who gathered also became more critical. O’Connell and others suggest that when neither meat nor more nutritious plant foods like nuts were available, our ancestors fell back on large underground tubers that plants in dry areas use to stockpile carbohydrates.
“These storage organs occur throughout the savanna but are protected by a deep layer of sun-baked earth and are hard to extract. Savanna-dwelling baboons access shallower rhizomes and corms, and chimpanzees in the only population ever to be studied in a savanna habitat use pieces of wood to dig out shallower tubers, suggesting that australopithecines may have done so as well. But it takes special equipment to dig out larger, deeply buried tubers. This is why, except for a few burrowing mammals like mole rats equipped with shovel-shaped incisors, humans are the only primates who exploit this widely available but difficult-to-access food source.
“Even before cooking, the addition of tubers to the other plant foods gathered by women would have provided new incentives for food sharing between hunters and gatherers, as well as new opportunities for postreproductive women willing to enhance the survival of kin. For women who knew where to look and who were willing to walk long distances, dig into hard earth, and carry their bounty back to camp, tubers provided a widely available if not particularly palatable source of calories when other foods were in short supply.”
Of course, tubers gathered by old ladies just aren’t as exciting as prestige-earning big game. So maybe this is just another example of the promoters of the paleo diet being evolutionarily correct. Admittedly, wild tubers are not the same nutritionally as potatoes. But the idea that carbs or starchy vegetables are unnatural in the human diet is false. The demonization of the potato has gotten out of control.
*The amount of calories required by an individual is very specific to that individual, but I don’t think the reason that a large number of impoverished kids were getting less than recommended was that they group just happened to have lower calorie requirements.