Junkfood Science: Happy Peanut Butter Day!

January 24, 2008

Happy Peanut Butter Day!

Kids of all ages love peanut butter. Even dogs love PB treats. Peanut butter lovers even have their own website, with fun tidbits and recipes. For those cooks and bakers with sophisticated peanut butter tastes, there are 185 more recipes here.

While peanuts and PB taste great and are dandy in the nutrition department, one thing they won’t do is help anyone lose weight and become thin. Yes, there’s even been a peanut butter diet, but it didn’t work better than any other diet. That hasn’t stopped researchers from trying, however. Last month, we heard in the news that kids who snacked on peanuts and peanut butter lose weight.

The source of that news report was a study published in the December issue of Pediatrics. You may have heard it reported as the first school-based weight loss program for 'overweight' Mexican American children that had successfully helped all of them lose substantial amounts of weight and keep it off.

This intensive intervention program, called the Family Lifestyle and Overweight (FLOW) program, teaches lifestyle behavior changes, including ‘healthy’ eating and portion control, and increased physical activity. But what makes this childhood obesity program different, and purportedly work better than other programs to date, is that school snacks are replaced with peanuts or peanut butter and a fruit or vegetable. Peanuts, it’s believed, are a nutrient-dense food that helps kids feel fuller so they’re less likely to overeat the rest of the day, while providing “good” fats for heart health.

This study was conducted by researchers with Baylor College of Medicine and the United States Department of Agriculture-Agricultural Research Service (USDA/ARS) Children's Nutrition Research Center Houston, Texas. Sixty Mexican-American children at a charter middle school (ages 10-14, average 12 1/2) who were at or above the 85th percentile for BMI on growth curves (“at risk for overweight”) were randomly assigned to the intervention or control group.

The control group was self-directed and used a 12-week parent-guided manual focusing on healthy eating and physical activity, and behavioral strategies to promote child weight loss and long-term maintenance.

The intervention group participated in an intensive school program led by an instructor-trainer. It included a daily class for 12 weeks: four days a week involved outdoor physical activity and one day was an indoor ‘nutrition’ lesson to teach them healthy choices and portion control. That was followed by another 12 weeks of bi-weekly sessions. Each school day included a snack of peanuts or peanut butter with a fruit or vegetable.

To teach the children and their parents how to eat ‘healthy,’ all they were given a weight management book, Trim Kids, and parents participated in monthly meetings to teach them how to adapt family meals to ‘healthy’ foods to help the children lose weight. Foods were labeled “safety,” “caution,” and “danger” zone foods, with rules for determining how to categorize foods to eat. Safe foods included fruits and vegetables. Caution foods, which they were taught to limit, included low-fat meats and dairy, and starches. Danger foods that “can be dangerous to your health” consisted of foods with ≥ 5 grams of fat or ≥ 15 grams of sugar per serving. The children were taught to monitor their activity, food intake and weight.

The physical activity component was described like this:

During weeks 1 to 6, the physical activity intervention was administered using a modified circuit-training approach to maintain heart rate within a target zone and to develop a basic level of physical fitness. Activities included sports and fitness drills for building endurance, strength, and flexibility, during which time participants monitored heart rates to learn how to regulate intensity. During weeks 7 to 12, the stations were modified to focus on skill development for either school- or community- sponsored activities available for participants in their neighborhood or school. These included both team sports (eg, basketball, soccer, or softball) and leisure activities (eg, jumping rope, dance, or kickboxing).

A token system was used to encourage compliance, with the children getting points for each dietary and physical activity behavior. They could exchange the points each week for prizes.


The children were weighed and measured at enrollment, 3 months and 6 months. The first flaw you’ve already realized is that this study is too short to demonstrate any lasting, meaningful changes in weight. This is even moreso with pre- and pubescent children — ages of especially rapid changes in body composition and growth. Any short-term, temporary changes in health indices are equally immaterial, especially since changes in insulin resistance and cholesterol levels are normal during adolescent growth.

As we’ve learned, children grow in spurts — some get taller first and then fill out, while others plump up first and then sprout up in height. Puberty is a period of fast growth, with girls putting on significant amounts of fat as their bodies prepare for childbearing. Boys grow at different rates than girls and begin puberty later. Every child at a given age is at a different level of maturity, which can significantly affect where they fall on growth curves at any given time. Children with family genes for being heavier also tend to be taller, mature earlier and have advanced bone ages and fall higher on the growth curve compared to genetically smaller children. This study, however, made no adjustments for maturity.

Researchers at the University of Manchester have found that prepubescent children experience 3 to 6 unpredictable growth spurts, lasting 13 to 155 days, with stable periods of 8 to 52 days in between. They also found growth is seasonal and slowed over the winter and spurted in the spring. A 3 to 6 month study period is too short to make any conclusions as to an intervention’s long-term impact on size in growing kids.

Each child grows at his/her own rate and manner. What matters to pediatricians is whether each child is “tracking” on his/her individual growth curve and growing in a way that is normal for them. Since the children in this study are all growing, their BMI changes need to be compared to where they would fall on their normal growth curves. These researchers estimated the children’s ‘weight loss’ by how their BMIs compared to standardized BMIs for their age.

This study found that by 6 months the children who’d lost weight (an average of 0.17 kg during the first 3 months) were already rebounding (and weighed 1.33 kg above their starting point). This demonstrates a yo-yo pattern already setting in among these youngsters — not sustained weight loss or maintenance.

But health is what matters most, not weight. The FLOW intervention children fell off their growth curve by 10% in just 6 months (going from 90% percentile weight for their age, to 80%), while the other children continued to generally grow normally and follow their growth curves. Traditionally, children who fall off their growth curves are a concern as it can indicate the youngsters are not getting enough calories, fats and nutrition necessary for their brains and bodies to develop normally.

There is no evidence that the health of naturally larger children is benefitted by having them lose weight (or fall off their normal growth curve) when they are supposed to be growing.

There is no evidence that foods with fat or sugars are unhealthy for children or that teaching them to monitor their calories-in and calories-out leads to long-term weight loss. Nor does it teach normal eating and healthy relationships with food.

There is no evidence that teaching them to monitor their weight from the age ten teaches them positive body image or helps their well being. This study did no evaluation of the adverse effects of their program on the long-term health, mental or physical, of the children.

There is no evidence that circuit training, sports and fitness drills, and structured team sports promote lifetime interests and enjoyment of physical activity in youngsters.

Oh, and this study provided no evidence that peanuts and peanut butter offer special benefits for promoting weight loss or maintenance in ‘overweight high-risk’ Mexican-American adolescents. That was the conclusion of the study press release issued by the Peanut Institute, which supported this study.

However, that also doesn’t make peanuts or PB bad (for those without allergies), of course. It just reminds us that all foods can be enjoyed just because they’re good, not because they hold special magical powers, good or bad.

So, in honor of Peanut Butter Day:

Peanut butter bacon cookies anyone? :)

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