We examined the halo effect of a 2-year weight-loss diet trial, the Dietary Intervention Randomized Controlled Trial (DIRECT), on the weight and nutritional patterns of participants' spouses.
DIRECT participants in a research centre workplace were randomly assigned to one of three diets: Low-fat, Mediterranean or Low-carbohydrate. A sample of wives of the DIRECT participants, who attended support update meetings specific to their husband's diet during the first 6 months, were followed for 2 years.
Seventy-four women (mean age = 51 years, mean BMI =26·6 kg/m2).
Among the wives of husbands randomised to the Low-fat, Mediterranean and Low-carbohydrate diet, self-reported weight change was respectively −1·48 kg, −2·30 kg and −4·62 kg after 6 months, and +0·39 kg, −3·00 kg and −2·30 kg after 2 years. Weight loss among wives whose husbands were in the alternative diet groups combined (Mediterranean+Low-carbohydrate) was significantly greater than among wives whose husbands were in the Low-fat group after 6 months (P = 0·031) and 2 years (P = 0·034). Overweight wives experienced more weight loss. The weight change of couples was significantly correlated (r = 0·42, P < 0·001). Across all dietary groups, wives had significant improvement in their dietary patterns in all food groups according to their husbands' diets, mainly by a larger significant decrease in carbohydrate consumption in the Low-carbohydrate group (P = 0·013 compared to Low-fat). Six-month weight change among the seventy-four DIRECT participants whose wives took part in the group support sessions was −5·2 kg, compared to −3·5 kg among the 248 DIRECT participants whose wives did not take part in these sessions (P = 0·020).
Focusing on the couple as a unit could provide a cost-effective approach to weight-loss programmes.
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