Feeding mice a high-fat diet causes osteoarthritis to develop at a younger age; however, our lab and others have observed differences in the timing and severity of osteoarthritis onset between different studies. Some labs use different amounts or types of fat, which could explain the variation. In our case, the difference between prior studies was in the control diets. One study used a standard lab chow diet and the other used a defined low-fat diet that matched our high-fat diet in all ways except for the amount of fat and carbohydrate in the diet. Osteoarthritis occurred sooner in our study that used the chow diet compared to the one using a defined low-fat diet. Therefore, we suspected that some component of the defined low-fat diet might also be causing some osteoarthritis and reducing the difference with the high-fat diet. The variable that caught our attention was a large amount of sucrose, which is a disaccharide composed of glucose and fructose. In people, fructose consumption independently causes dyslipidemia and abdominal adiposity. Therefore, we hypothesized that increased dietary sucrose was contributing to osteoarthritis. To test this, we compared metabolic and osteoarthritis outcomes in mice fed defined diets that independently varied sucrose content or fat content.
We found that only the mice fed the high-fat diet became obese. The mice fed the high-carb diet with more sucrose did not differ in body weight or fat from those fed a high-carb diet with low sucrose. Therefore, it was surprising when we found many metabolic and osteoarthritis-related differences between the mice fed the high-carb diets with different amounts of sucrose. The mice fed less sucrose (more starch) had a modest increase in early-stage cartilage damage, while the mice fed more sucrose had greater signs of joint inflammation. And the mice fed the high-fat diet showed both cartilage and bone changes related to osteoarthritis. In other words, each diet was associated with different features of osteoarthritis. This study suggests that the role of diet and metabolism may be much more important for maintaining healthy joints than we previously recognized. We need to pay closer attention to all dietary aspects and can’t rely on differences in body weight or fat to assess metabolic changes relevant to joint health.