Dropping 10% of body weight can reduce pain and improves function in overweight patients with knee osteoarthritis (OA), and losing an additional 10% may further reduce knee joint loading and improve quality of life, according to a secondary analysis of data from the Intensive Diet and Exercise for Arthritis (IDEA) trial

Stephen P. Messier PhD, and colleagues used 18-month data from the single-blind, single-center IDEA study to ask whether weight loss of at least 20% of baseline body weight would be associated with significantly greater improvements in pain, function, systemic inflammation, knee joint loads, and health-related quality of life compared with weight loss of 10% or more of baseline weight.

The researchers found, however, that just two measures (knee compressive force and health-related quality of life) showed further improvement among patients with weight loss of 20% or more vs. 10% or more. None of the other endpoints were significantly different, the researchers report in an article published online June 18 in Arthritis Care & Research.

Farshid Guilak, Ph.D., who was not involved in the study, told Medscape Medical News the changes observed are relatively small, and although they are statistically significant in some comparisons, they are not clinically relevant.

"Overall, the results are quite promising, but the separation into distinct categories of weight loss is somewhat arbitrary; i.e., 10% vs. 15%. A regression analysis might provide additional value in showing a relationship between weight loss and functional outcomes," said Guilak, who is the Laszlo Ormandy Professor.

IDEA study

The IDEA study enrolled sedentary, community-dwelling adults (age ≥55 years) who had mild or moderate knee OA (Kellgren-Lawrence grade 2 or 3), pain on most days, and body mass index between 27 and 41 kg/m2.

The IDEA subjects were randomly assigned to diet, diet plus exercise, or exercise interventions. Diet included partial meal replacements with commercial diet shakes, a weekly menu plan with recipes that were low in fat and high in vegetables, and weekly or biweekly weight monitoring during nutrition education and behavioral sessions, decreasing to a biweekly group and one individual session every two months from months 7 to 18.

For this observational secondary analysis, Messier combined 240 subjects from the diet and diet plus exercise groups and divided them into 4 categories based on weight lost at 18 months: less than 5% weight loss (n = 74), 5% to 9.9% (≥5%; n = 59), 10% to 19.9% (≥10%; n = 76), and at least 20% (n = 31).

In response to weight loss, pain decreased in a dose-response fashion, and function improved. The 10% or more and 20% or more groups had significantly less pain and better function than the groups that had lost less weight. However, differences in pain and function between the 10% or more and 20% or more groups were not statistically significant.

Similarly, both the 10% or more and 20% or more groups had better mobility and lowered interleukin six levels, which was the primary measure for inflammation, than the groups that lost less weight, but there was no significant difference between the 10% or more and 20% or more groups. According to Guilak, interleukin six values are likely to be dependent on adiposity, and correcting for body mass index overall may reduce the overall level of differences observed.

"It is not clear that such an observed change in knee compressive force is beneficial," Guilak cautioned. "Indeed, loading is necessary for joint health, and in general, the range of loading that occurs during daily activities (particularly athletics) greatly exceeds the range of differences observed here."

They suggest that the strong trend for pain (P = .012) and function (P = .0006) across weight loss groups, as well as the 25% mean reduction in pain and improvement in function between 10% or more and 20% or more weight loss, "argues that there may be additional clinical value with the greater weight loss."

In particular, the researchers note that enhanced self-efficacy and ability to tolerate feelings of hunger are psychological characteristics that appear to help achieve and maintain weight loss and that such psychological differences could not be ruled out because of the design of the study.

Overall, these findings provide additional support for the current National Institutes of Health recommendation of 10% weight loss as an initial goal for overweight or obese adults with OA and suggest that loss of an additional 10% of baseline weight might provide clinically important reductions improvements in pain and function.