Jicama is very close in the nutritional spectrum to a potato and can be substituted as such. The danger with potatoes (and their close relatives in the food family) is not so much the potato itself, but what we do to flavor it....toppings such as butter, sour cream, bacon, cheese, or sugar for sweet potatoes.... as well as the cooking technique used, such as frying. Be cautious on your preparation methods so you can be successful with potato-type products. They also have a higher glycemic index (GI), meaning the measurement of how quickly a food raises blood sugar once consumed—often triggering weight gain. Boiling and roasting shows the lowest GI as far as preparation techniques so they are best.
Bottom line, if you still trying to lose weight, be cautious on regularly eating jicama or potatoes until you have reached a maintenance level.