Seeking healthful diets for kids: Why some “natural" diets can harm children

© 2010 Gwen Dewar, Ph.D., all rights reserved

Everyone has heard about the perils of the high-fat, high starch, low-fiber diet common throughout the affluent, industrialized world.

So shouldn’t we steer our families toward a more “natural" diet? Eat the way we were meant to eat. Eat like our hunter-gatherer ancestors and enjoy better health.

It’s not a bad plan.

If you consider the diets of modern-day hunter-gatherers, several things stand out.

• They eat a wide variety of fruit and vegetables.

• Their carbohydrates tend to have low glycemic indices.

• They consume little sodium.

• They get plenty of vitamins and minerals.

• They eat very little saturated fat and get much more of the good fats—like omega-3 fatty acids—than do most Americans (Eaton et al. 1999).

But not every diet claiming to be “natural" is consistent with the research. Some are based on misunderstandings. Others on quackery and pseudoscience.

And when these diets take extreme form--eliminating whole food groups from the diet or severely restricting high-energy foods--these food plans pose special health risks for kids.

Extreme diets put kids at special risk because they have special needs (Bogin 1997; Kostyak et al 2007). Consider these points:

• Compared to an adult, a young child may spend three times as much of her resting metabolism feeding her brain.

• Her brain needs fat—especially omega-3 fatty acids—to grow.

• Her body needs fat, too. And not just for energy: Some vitamins can’t be absorbed without fat in the diet.

• For her body weight, a child burns more fat than an adult. (And yes, this has been demonstrated experimentally—see Kostyak et al 2007).

• Her smaller body is less energy efficient, and her digestive tract can’t extract as much energy from high-fiber, hard to digest foods.

• If she still has her “baby" teeth—which have shallow roots and aren’t as strong as permanent, adult teeth—she can’t chew up tough, fibrous, or hard foods to the same degree that adults can.

So we can’t expect kids to thrive on exactly the same diet that adults eat.

Kids--especially young children--need more energy and fat for their body weight than adults do. They can’t handle as much fiber as adults can. And this may explains whyyoung children are so picky about what they eat. Humans have evolved an early childhood preference for soft, easy-to-eat, high-energy foods.

How do we sort the good dietary recommendations from the bad?

Here are some basic guidelines.

Very low-fat diets aren’t good for kids.

Some kids living in affluent countries consume too much fat. But extremely restrictive fat intake isn’t good either.

Research suggests that kids should get at least 25-30% of their calories from fat. When fat intake dips below this level, kids are more likely to suffer from poor nutrition and lower growth rates (Bogin 1999; Butte 2000; Kostyak et al 2007).

And according to the American Dietetic Association, dietary fat should not be restricted in babies under 2 years old.

The bottom line? Low-fat diets designed for adults (to prevent heart disease, obesity, and other ailments) are not appropriate for the average child.

Very high-fiber intake can inhibit a child’s growth and cause malnutrition

Fiber is good for us, and studies suggest that most people living in affluent, industrialized countries don’t get enough.

But people who live in impoverished agricultural societies often have the opposite problem. And kids are particularly vulnerable.

Very high-fiber diets can cause problems, particularly if these diets include lots ofphytic acid, which is found in grains and legumes and inhibits the absorption of ironand other minerals.

When young children subsist on a diet that is very high in fiber and phytates, they may suffer from malnutrition. No matter how much they eat, they can’t get enough energy—or absorb enough vitamins and minerals—to meet their needs (Bogin 1999).

What constitutes a “very high-fiber diet"? No health agency has established a firm limit. But if you stick relatively close to the recommendations of the American Dietetic Association, your child’s fiber intake will be many times less than that of the malnourished kids mentioned above.

The American Dietetic Association has proposed the "age plus 5" rule, which means that each day a child should eat 5 grams of fiber plus 1 gram of fiber for every year old he is. After the age of 20, people should aim for 25 to 35 grams per day (Slavin 2008).   

Diets for kids that eliminate sources of B12, calcium, and other essential nutrients can have dire consequences.

Deficiencies of B12 and other nutrients can cause developmental delays, brain disorders, and impaired growth.

This explains why veganism and related diets (like macrobiotics) require careful planning to get right.

Diets that heavily restrict or exclude animal-derived foods are deficient in key nutrients. In theory, it’s possible to make up for these deficiencies with supplements. But in practice, some people don’t make the proper adjustments.

For example, human infants forced to subsist on macrobiotic diets have developed scurvy (Dagnelie et al 1990). And various studies have reported that vegan kids are deficient in vitamin B12 (e.g., Dagnelie et al 1004; Van Dusseldorp et al 1996; Larsson and Johansson 2002).

Beware of the “natural" raw food diet

There is nothing wrong with children eating some raw fruits and vegetables.

But diets for kids that consist of entirely and exclusively of raw foods? That's another story.

Contrary to what some zealots believe, there is nothing "unnatural" about cooked food. 

In fact, our hunter-gatherer ancestors began roasting their food long ago. And the introduction of cooking was probably a key event in human evolution, because cooking breaks down indigestible fibers and makes food easier to digest (Wrangham 2009).

When adults adhere to a strict, raw foods diet, they tend to become quite thin. For kids, such a diet will likely lead to malnutrition, developmental problems, and growth delays.

Beware of low-carb diets for kids

Low-carb diets that restrict the consumption of fruits, vegetables, milk, and whole grains may put kids at risk for vitamin and mineral deficiencies. These restrictions will also result in a diet that is too low in fiber.

Beware of plausible-sounding claims about “Paleolithic nutrition" and “ancestral" diets for kids

You might have heard the argument: We shouldn’t eat wheat or legumes or cow’s milk products because these foods weren’t consumed before 10,000 years ago. That’s not very long ago in evolutionary terms. So—the argument goes—humans haven’t had time to adapt to these new foods.

The problem with this argument is that it’s based on a false premise.

Ten thousand years isn’t very long, but it’s been enough time for many populations to evolve new physiological adaptations to the post-Paleolithic world. The best known dietary example is the evolution of lactose tolerance (Tishkoff et al 2007). But it’s likely that researchers will discover other cases in future.

The bottom line? While individual people might have good, personal reasons for avoiding specific foods, there is no logical reason for all people to reject all post-Paleolithic foods.

Some fans of the Paleolithic diet fail to recognize the difference between wild foods and supermarket foods.

Consider the vogue for low-carb diets that include the frequent consumption of red meat. To the degree that our hunter-gatherer ancestors ate red meat (and some ate surprisingly little), they were eating very lean, wild game. They weren’t eating domesticated livestock, which isn’t just higher in fat—it’s also higher in “bad" saturated fat and lower in “good" omega-3 fatty acids (Eaton and Cordain 1997).

So Paleolithic nutrition doesn’t justify eating lots of supermarket red meat.

But, as I suggest above, there is much to recommend the Paleolithic diet. For more information, see this article about hunter-gatherer nutrition and its implications for creating better diets for kids.

More information

For more articles about nutrition for kids, visit my index. 

References: Healthful diets for kids

Bogin 1997. Evolutionary hypotheses for human childhood. American Journal of Physical Anthropology

Dagnelie PC, van Dusseldorp M, van Staveren WA, and Hautvast JG. 1994. Effects of macrobiotic diets on linear growth in infants and children until 10 years of age. Eur J Clin Nutr. 48 Suppl 1:S103-11; discussion S111-2.

Dagnelie PC, Vergote FJ, van Staveren WA, van den Berg H, Dingjan PG, and Hautvast JG. 1990. High prevalence of rickets in infants on macrobiotic diets. Am J Clin Nutr. 51: 202-8.

Eaton SB, Eaton SB III, and Konner MJ. 1999. Paleolithic nutrition revisited. In W. R. Trevathan, E.O. Smith, and J.J. McKenna (eds), Evolutionary Medicine. New York: Oxford University Press.

Kostyak JC, Kris-Etherton P, Bagshaw D, DeLany JP, Farrell PA. 2007. Relative fat oxidation is higher in children than adults. Nutr J. 6:19.

Larsson CL and Johansson GK. 2002. Dietary intake and nutritional status of young vegans and omnivores in Sweden. American Journal of Clinical Nutrition 76(1): 100-106

Marlett JA, McBurney MI, Slavin JL. Position of the American Dietetic Association: Health implications of dietary fiber. J Am Diet Assoc. 2002;102(7):993-1000.Murphy SP and Allen LH. 2003. Nutritional importance of animal source foods. J Nutr. 133(11 Suppl 2):3932S-3935S.

Tishkoff SA, Reed FA, Ranciaro A, Voight BF, Babbitt CC, Silverman JS., Powell K, Mortensen HM, Hirbo JB, et al. 2007. Convergent adaptation of human lactase persistence in Africa and Europe. Nature Genetics 39:31-40.

Van Dusseldorp M, Arts IC, Bergsma JS, De Jong N, Dagnelie PC, and Van Staveren WA. 1996. Catch-up growth in children fed a macrobiotic diet in early childhood. J Nutr. 126(12):2977-83.

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