IT might while away a few hours during the Christmas holidays. How many points for virtue have you all racked up over the past 24 hours?

The game is made possible by an American system for assessing the nutritional value of all food in one number, summing up a lot of separate scores for good and bad content.

The Overall Nutritional Quality Index (ONQI), developed by scientists, has been turned into a commercial product, the NuVal system, which two US supermarket chains are now working to apply to about 4,000 products.

The announcement of the deal caused a ripple of interest around the world, because it lends itself to the easy production of league tables – like ours.

Blueberries and broccoli score the maximum 100. The saltine cracker, which Americans like as a bar snack, scores 1. The humble turnip is as good as some fashionable fruit. So, surprisingly, are some lettuces. But coconut and raisins are down there with pork chops. And it might be some comfort to learn that lobster turns out to be a lot less good for you than haddock.

The system gives points for the presence of vitamins and fibre and protein and for the absence of salt and fat, and so on. It
also scores low for high calorie content. One result is that "sodium-free sparkling water" scores 56 points, so it is not necessarily the best system for planning a diet.

But NuVal says that it enables useful comparisons to be made within groups of food. It is easy to see that skinless turkey breast scores much higher than burger mince, for example.

The NuVal website sums up: "All meats provide nearly perfect protein – only egg white is a more perfect source of the essential amino acids. Meat also is a good source of some B vitamins and minerals. But meats can also provide saturated fat, cholesterol, and varying amounts of sodium. Scores in this category range from 53 to 24. They tend to vary, based on the content of saturated fat and sodium in particular.

"While lean meat may be a very important part of a balanced diet, it will never score as high as most vegetables. That is because the NuVal System measures the ratio of nutrients to calories, and meats are generally a much more concentrated source of calories than fresh produce. So don't look for a NuVal score of 100 in this category; instead, compare meat scores to one another to find the items that are the most nutritious in this category."

Chief inventor David Dr Katz says: "There are no 'good' or 'bad' scores. Sometimes you'll choose a product just because you love it, and there is nothing bad about doing so. Balance and variety are important considerations, so foods across all categories, with scores all the way from 1 to 100, can, and should, be a part of your diet and your family's diet. That said, the more frequently you choose foods with relatively high scores, the better your overall nutrition will be."

So far, the system does not give any points for organic growing, but Katz says that it is designed to incorporate any new evidence which makes the grade scientifically. However, the UK Food Standards Agency is not convinced. It is still backing its own traffic-light system. Sainsbury's own-brands, among others, carry four dots in red, green and/or amber, to indicate levels of the four substances most blamed for ill health – sugar, fat, salt and the invisible "saturated fats" associated with cholesterol production.

Meanwhile, Tesco is leading trials of its preferred system, known as GDA, for Guideline Daily Amounts.

The Food Standards Agency plans to review the experience of both systems for a report next spring, which will recommend the way forward. So far, it's all voluntary, but there is a lot of enthusiasm in government for a binding universal system.

A spokesman for the FSA said: "There is obviously some appeal in the ONQI system but we do not think it is the right one. It takes in 21 measures and some relate to tiny amounts of things like magnesium, which most people are not really bothered about. Not all of them are necessarily listed as ingredients as a matter of course and it would be a big job to get all the necessary detail for all foods.

"Also, giving one score does not help if you are particularly trying to avoid sugar because you are diabetic, for example."

However, there is nothing to stop any shop from offering ONQI scores on its own initiative, and NuVal says that it has had expressions of interest from the UK, which will be followed up when the American pilot projects are better established.

More at nuval.com. See http://tinyurl.com/5d2b2c for a useful list.

Value added foods

90-100: Apricots, Asparagus, Green Beans, Blueberries, Broccoli, Cabbage, Cauliflower, Kiwi, Green Lettuce, Okra, Orange, Spinach, Strawberries, Turnip, Carrots, Grapefruit, Pineapple, Plum, Grapes, Honeydew Melon, Rhubarb.

50-90: Oatmeal, 88; Salmon Fillet, 87; Iceberg Lettuce, Halibut, Catfish and Cod, 82; Bok Choy (Chinese cabbage) and Oysters, 81; Milk (1 per cent fat), 81; Passion Fruit, 78; Prawns and Shrimp, 75; Clams, 71; Canned Tuna (drained of oil), 67; Canned Pineapple, 60; White Rice, 57; Milk (2 per cent fat), 55; Milk (whole), 52.

40-50: Pasta, 50; Prunes, 45; Turkey Breast (skinless), 48.

30-40: Lobster, 36; Pork or Beef (best lean cuts), 30-35; Turkey Breast (with skin), 30-31.

20-30: Pork Chop, 28; Chicken Wings, 28; Minced Beef (with standard fat content), 26-28; Lamb, 28; Ham, 27; Raisins, 26; Coconut, 24.

10-20: Fried Egg, 18; Swiss Cheese, 17; Dark Chocolate, 10.

0-10: White Bread, 9; Salami, 7; Cheese Puffs, 4; Milk Chocolate, 3; Apple Pie, 2; Fizzy Drink or Ice Lolly, 1.

Scores out of 100, from various sources, using the Overall Nutritional Quality Index.