Deborah McNaughton and Melinda Weinstein want us to face a simple truth: Many people consume too many calories and their unhealthy eating is costing them a piece of prosperity.

“Life would be a whole lot easier if our bank accounts grew and our waistlines stayed in the lower-digit range,” McNaughton and Weinstein write in their new book, “Rich and Thin: Slim Down, Shrink Debt & Turn Calories Into Cash.”

This mother-and-daughter team has come up with an interesting twist on the typical personal finance book. The two provide a guide to building wealth by battling the bulge.

Their book could be dismissed easily because of its “let’s all be healthy, wealthy and wise” shtick. But it’s a fact that an increasing percentage of Americans are overweight. Sixty-six percent of U.S. adults were overweight or obese in 2003 and 2004, according to researchers at the Johns Hopkins Bloomberg School of Public Health’s Center for Human Nutrition.

The fact is that all that weight is crushing people’s bank accounts. There’s a cost to being unhealthy. You often pay more for insurance. But keep within a healthy weight range and you save.

McNaughton and Weinstein’s book contains a “Money Calorie Counter,” which details how much you can save by investing the money not spent on foods that are unhealthy.

For example, let’s say you give up the expensive mocha latte you get five days a week. At about $3.35 a cup (with whipped cream), you would save $871 and 104,000 calories a year. If you get a 69-cent donut, add another $179.40 a year and 46,800 calories. All told, that’s $1,050.40 a year. If you were to put the money just from the latte in an investment each month that yields a 10 percent return over five years, you would have $5,620.64; in 10 years your money pot would grow to $14,868.33, and in 20 years you could have $55,117.52

“Think about the debt that could be paid off,” the women say in their book.

The book contains several pages that show the cost, the pounds you pack on, and the money that consumers spend on a variety of fast-food items, sandwiches, sweets and drinks.

Along with calorie-counting tips, you get the usual personal finance advice. The women cover budgeting, getting rid of debt and home buying. This is a slim book, but with a lot of good financial advice.