Jared M Tucker and Dr. Larry A Tucker, Physical Education
Obesity is a big problem in the United States. The National Center for Health Statistics indicates that more than one in every three American adults is either overweight or obese. Unfortunately, individuals with excess body weight, and especially excess body fat, are at high risk for many health problems, including coronary heart disease, Type II diabetes, hypercholesterolemia, hypertension, and several cancers. Obesity also leads to premature mortality, with more than 300,000 deaths in the United States due to obesity every year.
There are a variety of causes of obesity. However, behavioral factors are likely more important than genetic influences. Excluding genetics, the main causes of obesity are thought to be inadequate energy expenditure and excess energy intake. Excessive energy intake is usually accounted for by an over-consumption of foods that are high in calories, particularly high fat foods.
Dietary fat creates a significant problem with weight management because each gram of fat consumed provides nine Calories (kilocalories) of energy. Conversely, proteins and carbohydrates provide only four calories per gram. Obviously, eating foods that are high in fat will result in higher overall caloric intake when compared to diets that are high in carbohydrates or proteins, thereby increasing the risk of obesity.
Though carbohydrates and proteins have relatively low energy densities, dietary fiber is even lower. In fact, fiber provides zero calories per gram. Fiber is a complex carbohydrate that originates from plants that cannot be broken down and digested because the human digestive tract lacks the necessary enzymes. Logic would suggest that individuals who consume high amounts of dietary fiber would tend to be leaner than their counterparts, because fiber does not provide any energy. In short, fiber “fills you up, but not out.”
Despite the fact that research shows that dietary fiber is related to reduced risk of several disorders, including diverticular disease, irritable bowel syndrome, colon cancer, heart disease, and diabetes, more research is needed describing the effects of dietary fiber intake on body fat levels.
The purpose of this study was to determine the extent to which dietary fiber intake is associated with body fat percentage in middle-aged women.
A total of 237 women were used as subjects in this study. All participants signed an informed consent document, approved by BYU’s IRB, before participating in the study. Subjects were asked to report to the Human Performance Research Center in 120 Richards Building. After the study was explained and subjects completed the informed consent requirement, they were asked to change into a BYU swimsuit. Height and weight were then measured, followed by assessment of body fat percentage using the Bod Pod. Repeated measurements were taken in the Bod Pod until two measurements were within one percentage point of each other. The average of these two values were used to index body fat percentage.
After subjects changed back into their normal clothes, participants were educated regarding how to keep their food records. Subjects were trained using plastic food models and they were encouraged to record everything they ate and drank during the next seven consecutive days. Participants were also given written instructions reviewing the proper food recording protocol. Additionally, each subject was given a sample food log and seven blank diet logs, one for each day of the week.
To reduce problems associated with inaccurate judgment of food portion sizes, all subjects were trained with and issued a calibrated Ohaus 2000 portable electronic scale, which gives digital readings to the nearest gram. Subjects were instructed to use the scales to weigh everything they ate and drank during the 7-day recording period.
As a measurement of body fat percentage, the Bod Pod is considered valid and reliable. Bod Pod results are highly correlated (r > 0.90) to results produced by hydrostatic weighing and DEXA. Also, test–retest findings tend to be highly related (r > 0.98), indicating very good reliability.
The 7-day, weighed diet record is considered one of the best field measures of dietary intake. Most researchers consider this method of dietary assessment to be better than food frequency questionnaires and the 24-hour recall approaches.
The association between dietary fiber intake and body fat percentage were evaluated using the Pearson Product-moment correlation. The extent to which mean body fat levels differ across groups divided according to fiber intake were determined using analysis of variance and regression analysis. Control of possible confounding factors was assessed using partial correlation and multiple regression analysis.
Subjects were divided into four equal groups (quartiles) based on their dietary fiber intake. The four groups were then reduced to three groups by combining the two intermediate groups. Participants who consumed the least amount of fiber (group 1) had the highest level of body fat (mean 33.6%). Those in the intermediate fiber group (group 2) averaged 32.5% body fat, whereas subjects in the highest fiber intake group (group 3) had the lowest level of body fat (mean 31.8%). However, the body fat differences among the three groups were not statistically significant (F=0.81, P=0.446). Controlling for differences in age and energy intake strengthened the relationship, but it remained non-significant (F=1.7, P=0.193).
The Pearson Product-moment correlation coefficient was –0.08 (P=0.210), indicating a weak negative association between dietary fiber intake and body fat percentage.
Most research suggests that increasing consumption of dietary fiber promotes weight loss. This is primarily because dietary fiber fosters satiety without providing energy. In the present study, consumption of dietary fiber was not related significantly to body fat percentage. Apparently, more research is needed in this area.