Children with high blood cholesterol levels can benefit from reducing the amount of fat, saturated fat, and cholesterol in their diets without adversely affecting their normal development during puberty, according to new results from a long-term study funded by the National Heart, Lung, and Blood Institute (NHLBI). The study appears in the February issue of the journal Pediatrics.
In the Dietary Intervention Study in Children (DISC), children who adopted a recommended low-fat, low-cholesterol diet decreased their intake of total fat, saturated fat, and cholesterol within the first year of the study and maintained lower levels for several more years. These dietary modifications did not alter the children's growth, nutritional status, or sexual maturation throughout the seven-year study. Furthermore, the diet helped the children significantly decrease their blood levels of low-density lipoprotein (LDL) the "bad" cholesterol for up to three years.
"This is the first study of this size to examine the long-term effects of reduced dietary saturated fat and cholesterol intake among children," said Dr. Claude Lenfant, NHLBI director. "DISC confirms that dietary changes in children with high levels of LDL cholesterol may thwart the development of atherosclerosis without adverse effects."
During the past decade, scientists have found increasing evidence that atherosclerosis begins in childhood and that children and adolescents with high cholesterol levels are more likely than those with normal or low levels to have high cholesterol levels as adults.
In a 1991 report, the National Cholesterol Education Program's (NCEP) Expert Panel on Blood Cholesterol Levels in Children and Adolescents recommended cholesterol screening for children and adolescents with a family history of early heart disease or with a parent who has high blood cholesterol. Children and adolescents from such high-risk families who are found to have elevated blood cholesterol levels are advised to follow a diet low in saturated fat and cholesterol. In addition, the panel suggested population-wide approaches to lower the average blood cholesterol of all American children and adolescents by reducing their consumption of saturated fat, total fat, and cholesterol. But some scientists have questioned whether reducing fat in children's diets might cause problems such as growth retardation, nutritional inadequacy, and adverse psychological effects among pre-pubertal children.
"DISC addresses these concerns," added Dr. Eva Obarzanek, NHLBI project director. "Because this study examines children through several years during key stages of development, we can measure the effects of dietary modifications in the context of physiological changes during puberty."
DISC was conducted at six medical centers and involved more than 650 children who began the study at ages 8 through 10. Eligible participants had levels of LDL cholesterol that were considered borderline to high (111.5 mg/dL or higher for boys and 117.5 mg/dL or higher for girls).
Children were randomly assigned to either the intervention group or the "usual care" group. Those in the intervention group participated in periodic sessions with nutrition counselors to help them follow a regimen similar to the NCEP's therapeutic Step Two Diet to lower LDL blood cholesterol levels: 28% of calories from total fat, less than 8% from saturated fat, up to 9% from polyunsaturated fat, and fewer than 150 mg of cholesterol per day. Participants in the usual care group received information on general dietary recommendations but did not attend any intervention sessions.
Researchers observed no significant differences in height, weight, sexual maturation, or levels of serum ferritin (iron) between the intervention group and the usual care group. In addition, participants in both groups consumed comparable quantities of key vitamins (A, C and B-6), calcium, and zinc.
Blood tests to measure total cholesterol and LDL cholesterol levels were performed after one, three, five, and seven years. Throughout the study, blood cholesterol levels in the intervention group were lower than those in the usual care group, with significant differences between the groups found at one year and three years. At three years, LDL cholesterol levels of DISC participants in the intervention group were on average 2.5 percent (3.3 mg/dL) lower than the levels of those in the usual care group. (Findings from the study's first three years were published in the May 10, 1995, issue of the Journal of the American Medical Association.) The differences between the intervention and usual care groups in total blood cholesterol and LDL cholesterol levels narrowed over time, however, and they were no longer statistically significant at five years and seven years.
One contributing factor to this narrowing of differences was "a gradual improvement in dietary habits in the usual care group, which helped to lower their blood cholesterol levels," according to Dr. Obarzanek. At about five years from the start of the study, participants in the usual care group began consuming dietary cholesterol in amounts similar to those reported by the intervention group, making the differences in dietary cholesterol intake between the groups no longer significant by the end of the study (year 7).
The amount of saturated fat and total fat intake among participants in the usual care group also began approximating that of the intervention group at about the fifth year, although the differences in dietary fat consumption between the two groups remained significant throughout the study. At the seven-year assessment, the percent of saturated fat intake dropped on average from 12.5% to 10.2% of calories in the intervention group, and from 12.7% to 11.3% of calories in the usual care group. In addition, total fat intake in the intervention group dropped on average from 33.4% to 28.5% of calories; in the usual care group, total fat dropped from 34.0% to 30.6% of calories.
Scientists and nutrition experts view the improved dietary habits of the children in this study as encouraging and reflective of positive trends in the general public. Population surveys performed by the National Center for Health Statistics over the past few decades, for example, have shown that adolescents are consuming less total fat, saturated fat, and cholesterol.
"The results of these surveys coupled with the new DISC findings indicate that pediatricians, parents, and children are getting the message that it is important to start early to follow a low saturated-fat and low-cholesterol diet," Dr. Lenfant added.
Another factor that may have contributed to the narrowing of the differences in blood cholesterol levels between the two groups is lower adherence to the dietary recommendations by intervention group participants in the later years of the study, when they attended fewer intervention sessions. When investigators analyzed the blood cholesterol levels among only those participants who were most actively engaged in the study (those who attended all clinic visits), they found that the intervention group had significantly lower blood levels of LDL-cholesterol than the usual care group for as long as five years.