Potatoes are certainly not just pure starch (letter 31/10) but are a nutritious and satisfying food. They are an excellent source of Vitamin C and potassium and also contain calcium, magnesium, phosphorus, niacin (Vitamin B3), Vitamin B6, folate, choline and quercetin. They are also a good source of fibre.
Potatoes, especially when eaten raw, have anti-viral, anti-cancer and anti-inflammatory factors, and may be helpful in cases of eczema.
On the other hand, white bread and polished rice (white rice) are largely pure starch and white sugar is almost 100% pure carbohydrate.