Junkfood Science: Low-fat is not for kids

August 17, 2007

Low-fat is not for kids

A new study in Nutrition Journal could be invaluable to countless parents concerned about saturated fats in their children’s diets. Yet, despite the newsworthiness of this study and how many children and young women might be helped by the information, mainstream media has largely ignored it.

Low-fat diets are increasingly being promoted for children. With the intense public focus on healthy eating and obesity, many parents have understandably come to believe that restricting dietary fats can keep children from becoming fat and prevent heart disease. But are such diets normal and healthy for children?

Dr. John C. Kostyak at the University of Delaware led a small clinical study to examine how much fat the bodies of prepubescent children burn in order to support normal growth and energy needs. They examined ten children, ages six to ten, by first feeding them a carefully monitored weight maintenance diet for three days (all food was weighed to the nearest tenth of a gram and provided) to establish baseline metabolic measurements. They then measured the children’s fat oxidation using indirect calorimetry on three separate occasions before and after breakfast and then for 9 continuous hours in a room calorimeter or hood system calorimeter, where continuous metabolic measurements were taken. These measurements were recorded at rest and at low-activity levels to determine basic metabolic needs. These were compared to those of adults who underwent identical testing.

Every time the children were tested, their body fat oxidation in proportion to their energy needs were higher than the adults. In fact, the grams of fat oxidized relative to the calories they burned were 46% higher than adults. The researchers also found females (children and adults) oxidized more fat relative to calorie expenditures than males of the same age.

In other words, children’s bodies naturally need more fat to fuel growth processes, such as higher rates of protein synthesis, lipid storage and bone growth, and to meet their energy needs, the researchers said. Females also have higher nutritional needs for fat.

They reported that low-fat diets do not meet the nutritional needs for children and, instead, can interrupt normal growth and development. Sadly, diets recommending restricting fats to 30% of calories have been “translated by some in an overzealous, but well-intentioned, manner to provide as little fat as possible in the diet, leading to inadequate energy intake and compromised growth,” they said. The National Academies’ 2002 recommendations, they noted, are that children 1-3 years old to be allowed as much as 40% fat, and children and teens up to 18 years of age consumer up to 35% of their calories as fat (25-35%).

This is far different from what many parents and kids think. A recent post looked at how “healthy eating” messages have taught mothers and children to fear dietary fats and believe that low-fat and low-calorie foods are equivalent to good nutrition. The consequences of these misconceptions can be serious for children, yet few parents have ever heard that fat restrictions for children aren’t even universally supported in the medical literature. Low-fat diets have never been proven to be beneficial and could even be unsafe for children, concluded a review of the evidence by researchers at the Center for Food and Nutrition Policy at Georgetown University School of Medicine.

Yet fears of having fat babies and toddlers are leading some mothers to even dilute baby formula (breast milk is 40-50% saturated fat and cholesterol) and water down milk for toddlers, rather than give their children the whole milk recommended by pediatricians after the age of one.

Recently, the expert committee of the U.S. Preventive Services Task Force reported that, while low-fat diets for growing children are popular with “healthy eating” advocates, the evidence showed they are not effective in preventing obesity or heart disease. The USPSTF did, however, find evidence for harm:

Nineteen studies of dietary fat restriction reported effects on growth, nutrient intake, laboratory safety parameters, or other adverse effects. Twelve studies reported normal height growth...In one study, growth failure occurred in 8 (20%) of 40 children with dyslipidemia, 3 (7.5%) of whom had nutritional dwarfing and no progression of puberty....There have been three reports of growth retardation and nutritional dwarfing in children on unmonitored [low-fat] diets...

These concerns are shared by a number of researchers, such as Dr. Michael T. Pugliese, M.D. and colleagues at the Department of Pediatrics, North Shore University Hospital, Manhasset, and Cornell University Medical College in New York. They found babies and children failing to thrive and falling short on linear growth on low-fat diets, which had led to shortfalls on nutrients, as well as calories.

The New York pediatricians found that the parents had been “concerned that the children would become obese, develop atherosclerosis, become junkfood dependent, and/or develop eating habits that the parents believed were unhealthy. The parents instituted diets consistent with health beliefs currently in vogue and recommended by the medical community for adults who are at risk for cardiovascular disease. These diets caused the infants [toddlers to preschooler aged] to experience inadequate weight gain and have a decreased linear growth rate.”

Fears of obesity in adolescence is also adversely affecting children’s development, Dr. Pugliese reported. “The child voluntarily restricts his food intake to avoid becoming obese and incurring its associated social and health stigmata.” Besides the adverse effects on their physical health, sadly, “parental health beliefs and expectations can also lead a child to acquire anorexia nervosa-like symptoms.” The idea that dietary manipulations can modify the chance of obesity is highly controversial, however, they explained. The strong genetic determinant to obesity was shown during studies on adopted children, for example, “where obesity could not be easily modified by environment.”

Dr. Kostyak and colleagues also reported other information that, while recognized in the medical literature for decades and mentioned here before, is probably news to most parents. “Progression through puberty includes rapid and major changes in many phsiological processes,” they wrote. “Several studies have demonstrated a decrease in insulin sensitivity during puberty.” These transient periods of insulin resistance during puberty are normal and associated with growth, hormonal changes and the natural fat that is put on during pre-teen and teen years. Medical professionals have long recognized this, as it typically increases the insulin dosage needs by about 30% in kids with type 1 (insulin-dependent) diabetes. But it can also mean that normal, healthy kids are at risk of being mis-labeled by overly zealous practitioners as being diseased with type 2 diabetes.

More than a decade ago, researchers in Pediatric Endocrinology, Metabolism, and Diabetes Mellitus at Children's Hospital, University of Pittsburgh, Pennsylvania, tested the fat and glucose metabolism of pre-pubertal and pubertal kids, using even more stringent clinical tests, and found similar results as Dr. Kostyak’s group. Both lipolysis and lipid oxidation in pubertal kids were even higher for their body sizes as compared to prepubertal kids, while insulin action was suppressed. These changes correlated with IGF-1 levels, confirming their hypothesis of the role of the known, normal increases in growth hormone levels during puberty. “[S]tudies combined with our data suggest that the rate of lipolysis in normal humans during growth and development is a continuum, being highest in the neonates with a gradual decline toward the values found in adults,” the researchers wrote. They believed “increased lipolysis during childhood is a means to sustain the physiological requirements for energy substrates necessary for growth.”

The science consistently shows the importance of fat in the diet, especially for growing bodies. Yet, it’s so sad that parents and children seldom get this information. They only hear of the need to eat “healthy” and avoid saturated fats, and avoid getting fat. They rarely hear that there is no evidence that low-fat diets are healthful for kids or young people, or that “healthy” diets prevent obesity or chronic diseases. They never hear that most young people are already eating fats and calories within the Dietary Guidelines, and have better diets than past decades. And they never hear that most young people are even well within the weights recommended by the government. The facts would call into question a crisis of childhood obesity and the need for massive interventions.

Most of all, children aren't helped by being frightened about "bad" foods, their growing bodies and horrible diseases that may befall them in old age. The healthiest thing for them might be for everyone to just lighten up.

© 2007 Sandy Szwarc

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