They lost the weight … why didn’t productivity increase?

It is pretty well known that poor health is related to lost productivity. And the links between unhealthy body weight—particularly obesity—and poor health are stronger still. Although the relationships between obesity, disease, and productivity are complex, combining these two simple ideas gives a pretty straightforward model of how obesity may contribute to more absenteeism and worse performance on the job.

So why did researchers at the University of Michigan find that 142 participants in a weight management program—the majority of whom lost at least 15% of their body weight—had no corresponding increase in productivity? The weight loss results are consistent with a successful program. What happened to the expected productivity gains?

The authors discuss some possible explanations for the lack of significant productivity findings, noting particularly that time spent participating in the program did not affect productivity adversely and may have negated some reductions in illness-related absences.

However, the lack of significant results may reflect the early stages of the analysis and the challenges of including control groups in intervention studies.

The study assessed weight loss and changes in productivity outcomes six months after the program began. While the authors remind us that "weight loss of 5-10% body weight has been shown to improve cardiovascular disease risk factors and glycemic control," six months may nonetheless be too soon for clinically meaningful health improvements to translate into substantively meaningful improvements in how people feel. We expect people to miss work due to illness not simply because they have a disease, but because they experience pain, immobility, fatigue, discomfort, or other symptoms that make showing up for work extremely unpleasant, if not impossible. A longer assessment period may provide more time for people to experience a reduction in symptoms related to complications of obesity—at least for absences, which by the end of six months were trending downwards as expected.

Identifying a comparable control group is generally a challenge for designing intervention studies. In the current study, this means that the researchers essentially test the hypothesis that people will weigh the same six months after they started the program, and reject this assumption if participants lose weight significantly.

This is reasonable enough, but only if we are confident that without an effective program, workers will not gain weight. To know what might have happened without the program, we would need to follow a group of workers who were very much like the participants over the same period of time.

The same can be said for productivity. It is possible that without the program, absences could have inched upwards, and performance could have slipped. As with health care spending, when it comes to mitigating the lost productivity impact of illness, bending an upwards curve would still count as a qualified success.

None of this is to suggest that the weight management program is ineffective. To the contrary: the favorable findings thus far may represent a conservative lower boundary for what a weight management program can accomplish. As the study continues, we look forward to results that represent a longer time frame.