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Official serving sizes are finally catching up with modern eating habits.

A 20-ounce soft drink would now be a single serving, and so would a whole cup of ice cream, under a major revamp of the familiar food label being released Thursday.

Federal health officials are proposing the first changes to food labels in more than 20 years, and they plan to bow to the reality that Americans do indeed guzzle down those giant bottles of soda in one go, and that half a cup of ice cream just plain doesn't cut it.

"We have a right to understand what's in the food we're feeding our families," first lady Michelle Obama said Thursday at the White House. "You as a parent and as a consumer should be able to walk into a grocery store, pick an item off the shelf, and tell whether it's good for your family."

"By law, the label information on serving sizes must be based on what people actually eat, not on what they 'should' be eating," the Food and Drug Administration said in a statement.

Administration officials say about half of Americans really try to use the food labels, and it's only fair to tell them how many calories are in a container, not just how many are in a notional serving.

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"For certain packages that are larger and could be consumed in one sitting or multiple sittings, manufacturers would have to provide 'dual column' labels to indicate both'per serving' and 'per package' calories and nutrient information," FDA says.

"Examples would be a 24‐ounce bottle of soda or a pint of ice cream. This way, people would be able to easily understand how many calories and nutrients they are getting if they eat or drink the entire package at one time."

They’ll also reflect changes in thinking about what makes us fat — with less emphasis on total fat and more on overall calories. The FDA also proposes making food companies put clearly on the label whether there’s added sugar in a product.

And the calorie count will show up in really big font.

The goal is to address the obesity epidemic. With two-thirds of Americans overweight or obese, it’s time to help people realize more clearly what they are putting into their mouths, Obama administration officials say.

An example of the FDA proposed food label. FDA

The changes are being announced as part of the fourth anniversary of Mrs. Obama's “Let’s Move” initiative. “So this is a big deal, and it’s going to make a big difference for families all across this country," she said.

The new proposed label would make the calorie and serving sizes more prominent, and it would swap out details on how much vitamin A and B a product has in it, instead requiring levels of vitamin D and potassium, which are important to control blood pressure, for bone heath and for a strong immune system. Iron and calcium will still be listed.

The administration estimates the total cost to the food industry would be $2 billion. There’s no timetable for the changes to take effect. A 90-day public comment period opens Thursday. Officials said any changes would be phased in gradually.

The new labels will reflect the latest science. While in the 1990s, fat was blamed for making people fat, studies published since then have made it clear that sugar and other processed carbohydrates are just as much to blame.

"The label information on serving sizes must be based on what people actually eat"

“While continuing to require ‘Total Fat,’ ‘Saturated Fat,’ and ‘Trans Fat’ on the label, ‘Calories from Fat’ would be removed because research shows the type of fat is more important than the amount,” the FDA said.

Some things won’t change. The calorie percentage will still be based on a recommended 2,000 calories per day diet

And some serving sizes will shrink. Yogurt is labeled to reflect an 8 ounce serving, but most people eat it in 6-ounce cups, so the labels will show that.

“For 20 years consumers have come to rely on the iconic nutrition label to help them make healthier food choices,” said FDA commissioner Dr. Margaret Hamburg.

“To remain relevant, the FDA’s newly proposed Nutrition Facts label incorporates the latest in nutrition science as more has been learned about the connection between what we eat and the development of serious chronic diseases impacting millions of Americans.”