If someone in your house does this, you have a better chance of losing weight

Hate following a strict diet? Just convince someone you live with to start eating healthier instead.

It sounds silly at first, but a new study out of Barcelona, Spain found that the family members and housemates of patients following a strict Mediterranean diet and exercise regiment often ended up losing weight themselves. 

Conducted by the Hospital del Mar Medical Research Institute (IMIM) in collaboration with various other Spanish health organizations and facilities, these findings indicate that simply living under the same roof as someone following a Mediterranean diet is enough to promote healthier eating habits and weight loss. 

Despite not participating in an intensive weight loss program outlined by Spanish doctors for their housemates, people living with those patients lost an average of 2.75 pounds after one year and just over 8.5 pounds after two years in comparison to a control group. Co-inhabitants generally reaped even more benefits if they usually ate with the patient and/or the patient usually cooked for the household.

Diving into the details a bit further, a total of 148 family members of patients enrolled in the weight loss program PREDIMED-Plus had their weight and health outcomes tracked for two years. PREDIMED-Plus is a program for obese people looking to lose weight and improve their cardiovascular health. It is centered on following a Mediterranean diet in conjunction with regular exercise.

Most of the examined housemates were the patient’s partner or significant other (75%), but others were siblings, parents, or children.

The PREDIMED-Plus program “achieved effects beyond just weight loss in the patient, and this extended to their family environment,” explains principal investigator Dr. Albert Goday, head of the section in the Department of Endocrinology and Nutrition at Hospital del Mar, a researcher in the Cardiovascular Risk and Nutrition Research Group at the IMIM-Hospital del Mar and a CIBERobn researcher. “The effect was contagious, in this context it was, fortunately, a beneficial ‘contagion’, resulting in weight loss and improved dietary habits.”

Dr. Goday went on to say that he doesn’t think other diets offer the same benefits to housemates and family members.

“Among the many possible dietary approaches to weight loss, the one based on the Mediterranean diet is the most easily shared within a family environment,” he notes.

Moreover, while exercise is also a big part of the PREDIMED-Plus program, researchers say it wasn’t that aspect of the approach that benefitted family members. A survey was handed out to housemates to gauge how much, if at all, they had adopted their family members’ eating or exercise habits. While many indicated eating healthier, few reported getting in more exercise.

So, final study author Dr. Olga Castañer, a researcher in the Cardiovascular Risk and Nutrition Research Group at the IMIM-Hospital del Mar and CIBERobn, concludes the weight loss seen among patients’ family members can be explained “by an improved diet since the same contagious effect was not observed in terms of physical activity among the patients and their relatives.”

“In addition to weight loss, there was greater adherence to the Mediterranean diet, which has intrinsic health benefits, such as protection against cardiovascular and neurodegenerative risks,” she adds.

What about the patients who actually followed the PREDIMED-Plus program day in and day out? They saw some serious benefits as well; among 117 enrollees, an average of 11.2 pounds was lost the first year, which increased to just under 15 pounds after two years had passed.

“These results demonstrate the contagion effect, the halo effect, of a treatment programme in the relatives of participants involved in an intensive weight loss procedure, as well as increased adherence to the Mediterranean diet,” Dr. Goday concludes. “The beneficial effect of the programme 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.”

Dieting is rarely fun, but these findings just go to show how much easier clean eating can be when we’re not all by ourselves. Perhaps diets sculpted for entire households instead of just one person are the next big dietary trend.

The full study can be found here, published in the International Journal of Obesity.