When author JJ Smith developed her latest nutrition plan, she hoped it would have fast results. But even she wasn’t expecting to lose 200,000 pounds in three months.

That’s an average of 10 pounds for each of the estimated 20,000 people — and counting — who’ve completed the program in her book, “10-Day Green Smoothie Cleanse” ($17). And based on the positive feedback that floods her Facebook group, her number could be accurate.

Smith, 44, who lives in Arlington, Va., designed the cleanse for herself as a way to detox after mercury poisoning in 2013. Because Smith didn’t want to embark on the regimen alone, she contacted friends and family to see if anyone else was interested. One hundred of them said yes.

That was just this past January. After seeing successful results, she quickly wrote a paperback about it. As of Monday, the book was the No. 2 bestseller on Amazon.com.

Smith didn’t invent green smoothies, so what makes her plan special? The choices, she says. Readers can do the full cleanse, which is three smoothies a day, plus high-protein snacks (hard-boiled eggs, nuts) and unlimited crunchy vegetables. Or, they can do a modified version, with two smoothies a day, snacks and a meal (salad, veggies and chicken or fish). No matter which they pick, they won’t starve.

“In one drink, there are more nutrients than a lot of people get in a week,” says Smith, noting that the high fiber content works wonders on a digestive tract.

Because it can be tough to make such a big change, Smith recommends starting on a Friday: “As your body adjusts, you’re going to be irritable. By the fourth day, you’re feeling better. By the eighth day, you want to do it two more weeks.”

Smith still advises switching back to a more solid diet after 10 days — although a green smoothie or two a day can continue to be part of a lifestyle for years, she adds.

Pam Booker, 47, of Bowie, Md., is a believer: “Everything she said would happen, it happened to me.”

Since doing the cleanse in February with 20 women in her Zumba class, Booker has shed 30 pounds and her worst food habits. (“I have no desire for bread now,” Booker says.) Her only concern about the plan is that it’s too popular: “Frozen fruit is so hard to get.”

Smith recently organized a shopping trip for “day one-ers” at the Wegmans in Lanham, Md., and she’s planning a green smoothie party in June. So those numbers will only be going up.

Pineapple Spinach Smoothie

2 cups of spinach
2 cups of water
1 cup of pineapple chunks
2 cups of frozen peaches
2 bananas, peeled
11⁄2 packets of stevia
2 tablespoons ground flaxseed
1 scoop protein powder (optional)

Place greens and water into blender and blend until mixture is a green juice-like consistency. Stop blender and add remaining ingredients. Blend until creamy. (reprinted from “10-Day Green Smoothie Cleanse”)