After my food rant the other day, I did a bit of research. How much the facts can be off depends ... on what class of it is. Below is what is allowed by the FDA, by class, straight from their code. There is a whole bunch more info there. If interested in all it has to say, the link is:
The short answer to how far different from the Nutrient Facts a food can be - for class three nutrient which is calories, sugars, total fat, saturated fat, cholesterol, and sodium - it is no more than 20%. Twenty percent, can be a heck of a lot of calories. Makes one wonder what the heck good calorie counting is. Or that for those of us counting maybe we just need to tack on an extra 20% to make sure we're still in our alloted amount.
One thing is for sure, 20% more really hammers how how much one should not be eating packaged/processed foods of most any type, even something that seems as simple and straight forward as tuna packed in water.
How Compliance Works -- Title 21 of the Code of Federal Regulations (21 CFR 101.9(g))
FDA analyzes food samples that have been randomly collected from lots to determine compliance with labeling regulations. The agency defines a food lot as a collection of the same size, type and style of the food that is designated by a common container code or marking, or that constitutes a day's production. The sample for nutrient analysis shall consist of a composite of 12 subsamples (consumer units), taken 1 from each of 12 randomly chosen shipping cases. FDA will then analyze the nutrient content of this 1 composite test sample.
The agency generally analyzes composites by appropriate methods found in the most recent edition of Official Methods of Analysis of AOAC International (AOAC International, Gaithersburg, MD, 16th edition, 1995, and yearly revisions/updates) (see below for additional information on selection of methods). The ratio between the nutrient level derived by analytical testing and the label value is calculated to determine whether the nutrient in question is in compliance with applicable regulations. The ratio is defined as:
(laboratory value / label value) x 100 = %
In order to evaluate the accuracy of nutrition label information against a standard for compliance purposes, FDA regulations define two nutrient classes (Class I and Class II) (21 CFR 101.9(g)(3)) and list a third group (Third Group) of nutrients (21 CFR 101.9(g)(5)). Class I nutrients are those added in fortified or fabricated foods. These nutrients are vitamins, minerals, protein, dietary fiber, or potassium. Class I nutrients must be present at 100% or more of the value declared on the label ; in other words, the nutrient content identified by the laboratory analysis must be at least equal to the label value. For example, if vitamin C is added in a fortified product and the label states that vitamin C is present at 10% Daily Value (DV), the laboratory value must equal at least 6 mg of vitamin C/serving (i.e., 10% of the 60 mg Reference Daily Intake (RDI) for vitamin C that is specified in 21 CFR 101.9(c)(8)(iv)). The ratio between a laboratory finding of 4.8 mg vitamin C/serving (i.e., 8% DV) and the label value of 10% DV would be calculated as follows:
(8% / 10%) x 100 = 80% or (4.8 mg / 6 mg) x 100 = 80%
and the label value would not be in compliance.
Class II nutrients are vitamins, minerals, protein, total carbohydrate, dietary fiber, other carbohydrate, polyunsaturated and monounsaturated fat, or potassium that occur naturally in a food product. Class II nutrients must be present at 80% or more of the value declared on the label. As an example: If vitamin C is a naturally occurring nutrient in a product, and the product declares 10% DV vitamin C (i.e., 6 mg/serving) on its label, then laboratory analysis must find at least 80% of the label value (80% of 6 mg or 4.8 mg vitamin C/serving) for the product to be in compliance.
The Third Group nutrients include calories, sugars, total fat, saturated fat, cholesterol, and sodium. However, for products (e.g., fruit drinks, juices, and confectioneries) with a sugars content of 90 percent or more of total carbohydrate, to prevent labeling anomalies due in part to rounding, FDA treats total carbohydrate as a Third Group nutrient instead of a Class II nutrient. For foods with label declarations of Third Group nutrients, the ratio between the amount obtained by laboratory analysis and the amount declared on the product label in the Nutrition Facts panel must be 120% or less, i.e., the label is considered to be out of compliance if the nutrient content of a composite of the product is greater than 20% above the value declared on the label. For example, if a laboratory analysis found 8 g of total fat/serving in a product that stated that it contained 6 g of total fat/serving, the ratio between the laboratory value and the label value would be (8 / 6) x 100 = 133%, and the product label would be considered to be out of compliance.
Reasonable excesses of class I and II nutrients above labeled amounts and reasonable deficiencies of the Third Group nutrients are usually considered acceptable by the agency within good manufacturing practices.