A Virginia woman says she’s lost more than 80 pounds by dining exclusively at Starbucks. Now that’s a “latte fat!”

In order to shed the pounds, Christine Hall, a 66-year-old librarian, consumed mostly black coffee, hot oatmeal, and bistro boxes from the popular coffeehouse for more than two years. Starbucks made her weight loss convenient and easy, she told NBC News, because they list calorie counts on their labels, enabling her to track her intake online.

Registered dietitian Lauren O’Connor applauds Hall’s accomplishment, but says you can chalk it up to simple mathematics rather than some magical ingredient in the French roast.

“You lose weight when you create a caloric deficit no matter what foods you choose,” O’Connor points out.

O’Connor says Hall’s record keeping was a big reason why she succeeded in losing so much weight. It held her accountable to an average intake of just under 900 calories a day. And perhaps it also made her think twice about reaching for that 730-calorie walnut sticky bun when she could get the same sugar rush from the 160-calorie cinnamon walnut rugulach.

Theoretically any fast food can work as a sort of reverse Supersize Me diet if you watch the calories. “Jarod the Subway Guy” dropped 245 pounds in a year by eating only at the popular sandwich chain.

Many other major fast food franchises now post the calorie counts to help consumers stay on the lighter side of the menu. If the 2010 national health-care law goes into effect, calorie postings will be a legal requirement for all restaurants with 20 or more locations.

O’Connor does have health concerns about eating an all-takeout diet. Take Hall’s beloved bistro boxes.

“They may calorically fit well into a diet plan, but they contain a lot of processed ingredients like cheese and rolls,” she notes. “They contain some fruit, but where are the veggies? Even when they’re included, there’s little in the way of variety--and sodium counts are often through the roof.”

What about cost? At first glance it seems that Hall’s wallet probably lost a ton of weight too. But assuming she stuck to the plan and bought no additional food, she may not have done too badly.

A quick and dirty estimate based on her calorie intake and food choices suggests Hall probably spent somewhere in the neighborhood of about $22 a day--$154 dollars a week--to sustain her Starbucks exclusive diet. (Prices vary by item and geographic location.)

Compare this to what the average American spends on food each week according to the latest Gallup poll: $151.

Still, O’Connor says you’re better off preparing most of your meals at home.

“I think in a pinch, you can find decent items at a fast food place to fill in for a reasonable lunch or snack, but it’s best from a nutritional stand point to be in charge of your own meals to ensure you get the balance of vegetables, protein, whole grain, fruit and healthy fats.”

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