As obesity rates in North America continue to skyrocket to record levels a new book is joining the fight against growing waistlines.

Michael F. Roizen and Mehmet C. Oz's book "You: On a Diet" currently occupies the top spot on Amazon.com's best seller list.

Unlike most diet books, the two diet doctors aren't offering a miracle; instead they are offering an education.

"We want to diet smart, so it's not dieting hard," co-author Roizen told Canada AM.

Their latest book offers a clear understanding of the science behind our cravings and digestion.

The book also busts popular diet myths that can be counter productive to slimming down.

Each day this week Canada AM will look into five different aspects of maintaining a healthy weight.

• Monday: How we digest
• Tuesday: The biology of blubber
• Wednesday: The science of appetite
• Thursday: What we must and must not eat
• Friday: Taste tester - what kind of taster are you?

How we digest

Few people truly understand their digestive system, yet that is the first step towards maintaining a healthy weight.

Since it is the liver, and not the stomach, which plays the largest role in metabolism, Roizen stresses the importance of understanding how your liver digests different foods.

"Any food -- even lean protein -- goes to fat if you don't use it," Roizen explained.

Listed below are the ways your liver digests the four different types of calories.

Calories from fat

Calories from fat get broken down into smaller molecules and become absorbed as fat.

"Fat goes to fat and then it gets to your belly or someplace else," Roizen explained

But not all fat calories are bad calories.

Good fats, from foods such as nuts and fish, actually decrease your body's inflammatory response -- which is a contributing factor to obesity.

Calories from complex carbohydrates

Calories from complex carbs, such as whole grains, take longer to digest. They are converted to sugar much slower and reduce the stress on you digestive system.

"You want to give yourself sugar at a very slow rate. Which means get whole grains," Roizen said.

However, if you body cannot use the sugar, it too turns to fat.

"We think that carbohydrates and sugar go to sugar, and they do, but inside that magic liver, they turn to fat too," he said.

Roizen suggests making a habit of choosing whole grain foods.

But just because the packaging says whole wheat doesn't mean it's healthy.

"There are whole wheat fake outs," he said.

It's important to read labels carefully, because whole grain claims are often misleading or contain a lot of sugar.

Roizen suggests checking the sugar content per serving carefully, even when you don't expect sugar to be present in a product.

"You want to read the first five ingredients and if one of the ingredients says fructose, fancy molasses, sugar, or glucose, means it really has a lot of sugar in it."

According to Roizen, consumers should avoid buying any food with more than 4 grams of sugar per serving.

Calories from simple sugars

Sugar calories are absorbed by your liver the at the fastest rate. If your body doesn't use the energy immediately, your liver tells the body to turn that sugar into fat.

"You want to take in the simple sugars slowly so your liver deals it out slowly so you use them. Rather than a lot a once so your liver turns it to fat," he said.

Protein

Protein gets broken down into amino acids and end up in your liver. The acids are then sent to help build muscles.

But if you're not exercising your liver can't send them to your muscles, so they get converted to sugar.

"We think protein turns to muscle, but it doesn't. It turns to muscle, and other proteins, only if you have a little bit of it and you need it to build muscle," Roizen said.

"But most of the time you don't need it so it goes to sugar and then to fat."

Tuesday: Canada AM will look into the biology of blubber.