Osteoarthritis in lean Asians: Eating legumes can save the knee

Total fibre intake does not necessarily ward off the development of severe knee osteoarthritis (KOA) in a relatively lean population of Asians, but among dietary sources of fibre, eating a lot of legumes can help lower the risk of knee replacement due to severe KOA, as shown in a study from Singapore.

The protective association between legumes and total knee replacement (TKR) was dose dependent, such that there was a stepwise risk reduction—up to 14 percent—seen with increasing intake of legumes in a multivariate Cox proportional hazards regression model, according to the investigators.

Compared with the lowest quartile of intake (referent; 0.11 g/day), the second quartile lowered the risk by 2 percent (hazard ratio [HR], 0.98, 95 percent confidence interval [CI], 0.86–1.09), the third quartile by 5 percent (HR, 0.95, 95 percent CI, 0.84–1.06), and the highest quartile by 14 percent (HR, 0.86, 95 percent CI, 0.76–0.96; p_trend=0.004). [RMD Open 2021;7:e001602]

The estimates were not influenced by body mass index (BMI) and was consistent across BMI categories. On the other hand, the consumption of other fibre sources, namely grain products, nuts and seeds, soy food, and fruits and vegetables had a null effect on the risk of TKR.

The analysis was based on a cohort of 63,129 adults participating in the Singapore Chinese Health Study, among whom 2,816 cases of incident TKR (mean age at surgery 55.7 years, 82 percent women) occurred over a median follow-up of 19.6 years.

Compared with the rest of the cohort, individuals who underwent TKR had higher BMI (mean, 25.0 vs 23.0 kg/m²), higher prevalence of hypertension and smoking, were less likely to have diabetes, participated in less physical activity, and had longer sitting time.

“To our best knowledge, this is the first study to specifically report an inverse relationship between legume intake and risk of TKR due to severe KOA,” the investigators said.

The key strength of the study was that the BMI levels across the quartiles of fibre intake were quite homogeneous among the relatively lean participants, they pointed out. “Hence, expectantly, the associations between total fibre or food intake and risk of TKR were essentially unchanged in the models with and without BMI adjustment, thus indicating that any mediation or confounding effect from BMI was minimal.”

A previous US-based study has also shown a dose-dependent inverse association between nut and legumes and incident symptomatic and incident radiographic KOA. However, it evaluated nuts and legumes as a single item, unlike the current study which examined nuts and legumes as separate food items. [Ann Rheum Dis 2017;76:1411-1419]

Legumes, such as beans, peas, chickpeas, lentils, and lupin beans, are rich in nutrients that possess antioxidant and anti-inflammatory properties, which could possibly reduce low-grade systemic inflammation and activate mitochondrial oxidation. [Food Res Int 2017;101:1-16; J Med Food 2013;16:185-198; Br J Nutr 2012;108 Suppl 1:S103-110; J Med Food 2009;12:100-108]

“The generation of reactive oxygen species (ROS) and lipid peroxidation products has [been implicated] in the pathogenesis of the arthritic joint. Hence, it is possible that phytochemicals in legumes could reduce ROS production and salvage mitochondria dysfunction to slow down progression of osteoarthritis,” the investigators said. [Arthritis Rheum 2006;54:271-281; Osteoarthritis Cartilage 2018;26:989-991; Curr Opin Rheumatol 2018;30:101-107]

“Further research is needed to replicate our findings and [to establish] the biological mechanisms underlying the effect of dietary legumes on pathogenesis or progression of osteoarthritis,” they added.