Optimizing dietary fat in a weight-loss trial requires advice based on a structured “whole-of-diet” model

Abstract

Dietary trials may link macronutrient intakes to health outcomes, but adherence to dietary targets requires advice based on an understanding of food composition and consumption patterns. Using data from a weight loss trial, we hypothesized that structured advice would be required for significant fat modification to occur. We compared participants' food choice patterns in response to advice based on a structured "whole-of-diet" model vs a general approach to healthy eating. Overweight participants (n = 122) were randomized to 2 advice arms (saturated fat [SFA] < 10% energy [E]): (1) general low fat (LF) control-(a) isoenergy, (b) -2000 kJ; and (2) structured LF high polyunsaturated fat (PUFA) (∼10% energy PUFA; PUFA to SFA ratio ≥1) (LF-PUFA)-(a) isoenergy, (b) -2000 kJ. Intakes of E and fat and fat from food groups (percentage of total fat intake) were compared at baseline, 3 months, P < .05. Baseline diets were similar, with most fat from high-SFA foods (59%): meat and milk-based staple meals and high-fat snacks. By 3 months, all groups reduced E and met the SFA target. Polyunsaturated fat targets were met by the LF-PUFA groups only (P < .001), enabling targeted between-group differences. In response to general advice, LF groups simply switched to LF alternatives of the same foods (P < .05). In comparison, LF-PUFA groups shifted fat intake to high-PUFA choices (54%), consuming more fat than controls from nuts (P < .001), whole grains (P < .001), and oils and spreads (P < .05). Significant reductions in E were achieved regardless of advice, but significant shifts in dietary fat profile relied on structured whole-of-diet advice on a range of meal and snack food sources of fat subtypes.