​Both low-carbohydrate diets and low-fat diets share one drawback:

A) ​neither produces weight loss.
B) ​both are unhealthy.
C) ​modest long-term weight loss.
D) ​all of these are drawbacks.

Both low-carbohydrate and low-fat diets have been shown to produce only modest long-term weight loss, which can be a drawback for people looking for significant weight loss. However, it is important to note that the effectiveness of any diet depends on individual factors such as adherence to the diet, genetic makeup, and lifestyle factors.