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New research finds that the benefits of a person adopting a low calorie Mediterranean diet seem to extend to their family members. Klaus Vedfelt/Getty Images
  • Relatives of individuals participating in a weight loss program lost an average of 1.25 kilograms (kg), equivalent to 2.75 pounds (lb), during the first year.
  • They lost an average of 4 kg, or almost 9 lb, in the second year.
  • As family members did not also adopt the increased physical activity regimen that was part of the program, the researchers concluded that the halo effect was due to the change in diet.

A new study suggests that people living with someone participating in a weight loss program may also lose weight.

The team of researchers and doctors, who were from hospitals and research institutes in Spain, reported their findings in the International Journal of Obesity.

The researchers followed 148 relatives of 117 participants in the PREDIMED-Plus trial, which followed 6,874 people at 23 research centers in Spain from September 2013 to December 2016.

The researchers behind the new study invited 200 relatives from two of the 23 sites to participate. Of these, 148 participated in a baseline interview at the same time as their family member was taking part in the trial. A year later, 114 people provided follow-up data, and 2 years later, 76 family members provided data.

In the PREDIMED-Plus trial, the team randomly allocated the participants to one of two groups. The researchers asked the first group to eat an energy-reduced Mediterranean diet and do regular physical activity, with the individuals receiving behavioral support. The second group, which was the control group, ate an energy-unrestricted Mediterranean diet.

The relatives lost an average of nearly 3 lb more during the first year of the program compared with those in the control group and about 9 lb more in the second year.

“The effect was contagious,” says Dr. Albert Goday, the principal investigator on the study and head of section in the Department of Endocrinology and Nutrition at Hospital del Mar in Barcelona. “In this context, it was, fortunately, a beneficial ‘contagion,’ resulting in weight loss and improved dietary habits.”

The Mediterranean diet is based on the foods that people living in the Mediterranean region traditionally ate. Individuals adopting this diet typically eat a wide variety of fruits, vegetables, and whole grains, along with healthy fats such as nuts, seeds, and olive oil.

Of the many dietary approaches for weight loss, Dr. Goday maintains that “the one based on the Mediterranean diet is the most easily shared within a family environment.”

The weight loss that the family members in this study achieved is, the researchers believe, likely due to an improvement in their diets, as they did not see an increase in physical activity among the family members.

The study authors reported that family members who regularly shared lunch or dinner with the weight loss program participant experienced more significant weight loss and better adherence to a Mediterranean diet.

Additionally, they noted that “the participants who better transferred their diet changes to the rest of the family were the ones who cook at home.”

In addition to helping people lose weight, the Mediterranean diet protects against cardiovascular and neurodegenerative risks, according to the authors.

Earlier research has also suggested that behavioral changes can be contagious. A 2008 study, for instance, found that groups of connected people tend to quit smoking at once. In 2018, researchers reported that the spouses of individuals enrolled in weight loss programs also lost weight.

The Spanish researchers believe that it would be advantageous to conduct a larger study looking at whether it is beneficial for couples to engage in weight loss programs together. They would also like to see whether the contagion effect continues over the course of a lifespan.

“The beneficial effect of the [weight loss program] on one member of the family unit can be extended to its other members, which is extremely significant in terms of reducing the burden of obesity on the public health system.”

– Dr. Albert Goday