Cod is low in fat. When grilled, an average serving (120g) of cod provides 115 calories and 1.4g of fat. It is a valuable source of protein and contains potassium (380mg100g) and iodine (1305g100g), as well as zinc and a number of B vitamins, particularly B12 (25g100g grilled fish).
Potatoes are an important source of vitamin C. Amounts vary depending on how they are cooked: baked potatoes (with skin) contain more than chips, which contain more than boiled potatoes.
Potatoes are low in fat (around 0.1g per 100g) and provide fibre (in the skins), potassium, phosphorus and a range of B vitamins, including B6.
However, "the picture changes when these foods are fried," says Dr Hannah Theobald, nutrition scientist with the British Nutrition Foundation. "The average serving of battered cod (180g) provides a whopping 450 calories and 28g of fat. Add a small serving of chip-shop chips and that's another 240 calories and 12g of fat. The average woman needs 2,000 calories a day, so a serving would provide 35 per cent of her daily calorie requirement.
"The same can be said for fat. The average woman should consume in the region of 70g of fat per day, so a serving provides nearly 60 per cent of her fat requirement. Most people also add salt to the meal, and most of us in this country are consuming far too much salt."
Not all the goodness of potatoes is lost when chips are made. They remain a source of potassium and vitamin C. Battered cod also retains B vitamins and iodine when fried, and the batter contains calcium and iron (flour is fortified in the UK with these).
"A serving of cod and chips is a high-fat, high-calorie meal and should be consumed in moderation," says Dr Theobald. "To make it more balanced, add a serving of mushy peas. Of course, grilled cod and oven chips are a healthier option."