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Effects of reduced-fat diets consumed ad libitum on intake of nutrients, particularly antioxidant vitamins
B A Swinburn1, G A Woollard, E C Chang
1Department of Community Health, University of Auckland, New Zealand.
Objectives:
To determine whether a reduced-fat diet consumed ad libitum can achieve the recommended intakes of other macronutrients, fiber, and cholesterol and whether such a diet affects intake of other important micronutrients such as fat-soluble vitamins.
Design:
Twelve-month, randomized, controlled trial of a reduced-fat, ad libitum diet vs usual diet.
Subjects:
One hundred ten adults older than 40 years with glucose intolerance (2-hour blood glucose concentration = 7.0 to 11.0 mmol/L) who were selected from a previous workforce survey.
Intervention:
Monthly small-group meetings aimed at identifying sources of dietary fat and ways to reduce fat consumption.
Main Outcome Measures:
Nutrient intakes derived from 3-day food diaries at the beginning and end of the study. Blood levels of retinol, alpha-tocopherol, and beta carotene at the end of the study.
Statistical Analyses Performed:
Unpaired t tests for determining changes in nutrient intake and antioxidant vitamin concentrations. Separate analyses were conducted with users of mineral and vitamin supplements and people who changed smoking status to reduce potential confounding.
Results:
Fat intake decreased from 35% to 26% of energy in the reduced-fat diet group compared with a 2% decrease in the control group (P < .0001). Total energy intake also decreased in the 2 groups (-362 vs -59 kcal/day, P < .02). Those changes were reflected in a 3.1 +/- 4.7 kg (mean +/- standard deviation) weight loss in the intervention group compared with a 0.4 +/- 3.0 kg weight gain in the control group (P < .0001). There were no differences between groups in the changes in micronutrient intakes, except for an energy-adjusted increase in beta carotene intake in the reduced-fat diet group. Serum retinol and alpha-tocopherol concentrations were not different between the groups, but the reduced-fat diet group had higher beta carotene concentrations (P = .009).
Applications:
A reduced-fat, ad libitum diet can be prescribed to improve overall macronutrient intake and achieve modest weight loss without sacrificing micronutrient intakes.