The halo effect: Do weight-loss interventions affect family members? Original paper

Some evidence suggests that when people adopt lifestyle changes for weight management, members of their family change their behaviors as well — a phenomenon called the “halo effect”.^[1][2] While several studies have explored the halo effect of bariatric surgery and dietary interventions, more research is needed on interventions that combine dietary changes and exercise.

This 2-year prospective study examined the halo effect in 148 untreated family members of the 6,874 participants in a diet-and-exercise randomized controlled trial (RCT).

In the RCT,^[3] 6,874 people had been randomized to either a 2-year lifestyle intervention (hypocaloric Mediterranean diet, individualized physical-activity promotion, and behavioral support) or a control group.

The 148 family members analyzed for the prospective study didn’t receive lifestyle advice; they visited a clinic or simply completed questionnaires — at baseline, one year, and two years — to assess their body weight, adherence to a Mediterranean diet, and physical activity.

The family members of the people in the intervention group lost weight at one year (−1.25 kg, so −2.76 lb) and two years (−3.98 kg, so −8.77 lb), while the family members of the people in the control group gained weight at one year (+3.30 kg, so +7.28 lb) and two years (+1.90 kg, so +4.19 lb). The between-group difference was statistically significant at two years, but not at one year.

The family members of the people in the intervention group were also more likely to be following a Mediterranean diet, at both time points.

The weight changes of the people in the intervention group and the weight changes of their family members were correlated at both time points, despite the physical activity levels of the family members not having significantly changed from baseline.

Several other studies have assessed the halo effect among the spouses of participants in weight-loss lifestyle interventions.

• In a 2009 study, the spouses of participants randomly allocated to a Mediterranean, low-carb, or low-fat diet for 2 years lost 3.00 kg (6.61 lb), lost 2.30 kg (5.07 lb), and gained 0.39 kg (0.86 lb), respectively.^[1]
• In a 2008 study, the spouses of participants in a 1-year weight-loss intervention combining diet and exercise lost 2.2 kg (4.9 lb).^[2]
• In a 1992 study, the spouses of participants in a 1-year low-fat dietary intervention lost 0.95 kg (2.09 lb).^[4]
• In a 1991 study, the spouses of participants in a 6-month low-fat dietary intervention lost 1.1 kg (2.4 lb).^[5]