Low-fat Dietary Intervention Research Articles

Dietary Changes Among Husbands of Participants in a Low-Fat Dietary Intervention

A dietary intervention delivered to one family member with a beneficial impact on other members could provide a cost-effective approach to public health dietary intervention programs. The Women's Health Trial (WHT) was a study in which women were randomized to be trained in adopting a low-fat diet or to continue their normal diet. The intervention women consumed 21% of total calories from fat versus 38% for control women at six months postrandomization. Husbands of women in the Seattle Clinical Center of the WHT were surveyed between 1985 and 1988 to determine whether and to what extent the husbands' diets changed at six months. Ninety-one intervention men and 162 control men, 79% of those eligible, participated. Intervention men reported an average weight loss of 2.4 pounds, compared to an average 0.7-lb loss among controls (P = .03). Based on self-reported change of specific foods, we found that intervention men more often reduced butter, margarine, eggs, and red meat over the six months than did control men (P less than .001). Based on nutrient consumption estimated by a food frequency questionnaire, intervention husbands consumed 34% of total calories from fat versus 36% for controls (P = 0.04). The number of meals shared with wives per week modified the effect of the intervention: among the intervention group, for every three meals shared, an accompanying one percentage point reduction in percentage of calories from fat occurred in the husband's diet. Thus, we suggest that dietary intervention programs attended by one spouse appear to exert a small beneficial effect on the other spouse.

Aspects of the science of cancer prevention trials: Lessons from the conduct and planning of clinical trials of a low-fat diet intervention among women

Cancer prevention trials are contrasted with cancer therapy trials, cardiovascular disease prevention trials, epidemiologic cohort and case-control studies, and trials with surrogate endpoints, in order to highlight some of their unique features and in order to examine the role of such trials in the cancer prevention agenda. The implication of these features and this role are discussed with respect to trial rationale, trial design, and trial protocol, with planning exercises for proposed dietary fat intervention trials among women providing illustration. Finally, some considerations are mentioned for the planning of a primary prevention trial of breast cancer using tamoxifen.

Changes in food patterns during a low-fat dietary intervention in women

The Women's Health Trial was initiated by the National Cancer Institute to study the effects of a low-fat diet on the incidence of breast cancer in women at elevated risk for the disease. The purpose of this article is to examine the specific dietary changes that 173 women made while participating in a feasibility intervention program to reduce their fat intake to approximately 20% of total calories over a 12-month period. The intervention program used group sessions to teach nutrition information and behavioral skills necessary to make a life-style dietary change. Four-day food records were collected from participants at the beginning of the study and again at 12 months. Women in the intervention group reduced their total fat intake from a mean of 76 gm (39% of total energy) to 31 gm (22% of total energy), mainly by decreasing their fat intake from milk products, red meats, and fats/oils. These women used cheddar cheese, American cheese, whole milk, butter, mayonnaise, salad dressing, bacon, and hamburgers less frequently, and used diet American cheese, low-fat cottage cheese, and skim milk more frequently. They consumed less fat in their vegetable dishes, and their total caloric intake from fruit increased slightly. In addition, the overall quality of the diets improved, since there was a 20% to 50% increase in the energy-adjusted intake of vitamins and minerals from food sources.

Feasibility of a randomized trial of a low-fat diet for the prevention of breast cancer: Dietary compliance in the women's health trial vanguard study

The Women's Health Trial Vanguard Study was conducted to examine the feasibility of a nationwide, randomized multicenter intervention trial to test the hypothesis that a low-fat diet followed for a period of 10 years will reduce breast cancer risk. Women ages 45–69 years at increased risk of breast cancer were randomized into intervention (low-fat diet, n = 184) and control (usual diet, n = 119) groups. On the basis of 4-day food records, baseline fat intakes were comparable in the two groups, averaging 1,718 kcal with 39% of energy as fat. Intervention women reported substantially lower fat intake at 6 (20.9% kcal), 12 (21.6%), and 24 months (22.6% kcal). In contrast, control women reported only slight reductions in fat intake (37.3% kcal at 12 months and 36.8% kcal at 24 months). Evidence that these women were indeed complying with the low-fat dietary intervention comes from (a) the reasonable nature of reported nutrient changes within food groups in the intervention women and (b) agreement between observed and expected differences in plasma total cholesterol between the control and the intervention groups. At 12 months, the observed control - intervention plasma cholesterol difference was 13.1 ± 4.6 mg/dl while the expected difference based on the Keys equation was 15.1 ± 1.1 mg/dl; at 24 months, the observed difference was 15.5 ± 4.3 mg/dl and the expected difference was 12.0 ± 1.2 mg/dl. These analyses indicate that the intervention women made substantial dietary changes and have successfully maintained these changes over a 2-year period. This study thus demonstrates the feasibility of a randomized trial with an intensive low-fat dietary intervention.

Dietary Fat Reduction and Plasma Estradiol Concentration in Healthy Postmenopausal Women

Concentrations of total and weakly bound plasma estradiol were significantly (P less than .01) reduced in 73 healthy post-menopausal women after 10-22 weeks of participation in a low-fat diet intervention program. Nonsignificant reductions in estrone sulfate and sex hormone-binding protein were also observed. The 17% reduction in average estradiol concentration was accompanied by an average reduction of 12 mg/dL in total plasma cholesterol (P less than .001), an average weight loss of 3.4 kg (P less than .001), and an average reduction in daily dietary fat from 68.5 to 29.5 g. Our review of case-control studies indicates that a 17% reduction in plasma estradiol may explain a noteworthy component of the international variation in breast cancer incidence. We find a need for further studies of (a) disease risk in relation to hormone concentrations and (b) changes in hormone concentrations as a function of the duration of low-fat diet intervention.

Diet intervention methods to reduce fat intake: Nutrient and food group composition of self-selected low-fat diets

A multicentered pilot study was conducted to test an intervention protocol designed to reduce fat intake to 15% of energy intake. Eligible subjects were postmenopausal women with stage II breast cancer whose baseline fat intake was more than 30% of energy intake. The low-fat diet intervention protocol consisted of bi-weekly individual counseling sessions with emphasis on substitution of lower-fat foods for high-fat foods and maintenance of nutritional adequacy. Nutrient intakes were calculated from 4-day food records collected at baseline and after 3 months of diet intervention. Mean daily fat intake for the 17 patients on the low-fat diet dropped significantly from 38.4 +/- 4.3% of energy intake at baseline to 22.8 +/- 7.8% at 3 months (p less than .001). A 25% reduction in mean energy intake, from 1,840 +/- 419 kcal at baseline to 1,365 +/- 291 kcal at 3 months, was accompanied by significant increases in protein and carbohydrate as percent of energy intake. A mean weight loss of 2.8 kg and a 7.7% reduction in serum cholesterol were observed; both changes were significant at the p less than .01 level. Absolute intakes of zinc and magnesium were significantly reduced. However, mean intake on the low-fat diet for 14 vitamins and minerals, including zinc and magnesium, exceeded two-thirds of the 1989 Recommended Dietary Allowances (RDAs). When expressed as nutrient density (i.e., amount of nutrient per 1,000 kcal), increases were observed for all micronutrients. These results support the hypothesis that a nutritionally adequate low-fat diet can be successfully implemented in a highly motivated, free-living population.

Statistical design of the women's health trial

The National Cancer Institute has initiated a randomized trial to determine whether a low fat diet can reduce the incidence of breast cancer among women at increased risk for this disease. A feasibility trial involving 303 women has been conducted to examine recruitment strategies, study short-term compliance and, more generally, develop and refine trial procedures. The feasibility trial group also developed a detailed full-scale trial design plan, and randomization of participants to such a trial is currently underway. The purpose of this report is to describe the major design features of this Women's Health Trial, with particular emphasis on the statistical aspects of the design. The trial is planned to last 10 years and to include 32,000 participants. Of these 32,000 women, 12,800 will be assigned to a low fat diet intervention, and the other 19,200 will constitute a control group. The sample size of 32,000 arises from a range of estimates and assumptions pertaining to (a) the incidence of breast cancer at enrollment corresponding to selected eligibility criteria, (b) the relative risk of breast cancer as a function of a woman's history of dietary fat intake, (c) compliance assumptions in terms of average percent fat in the intervention and control groups as a function of time from randomization, and (d) rates of competing causes of death. These estimates and assumptions will be discussed, as will the robustness of the intended sample sizes to departures from such design assumptions.