Q: hi mike, i heard that calories is the main cause of becoming fat , so healthy carbs and fats does not make you fat. now i understand why food that comes in a box is bad, because are high in calories and will make you fat. is that right?

A: That's definitely part of the reason. Processed prepackaged foods tend to be higher in calories than natural foods... 4 ounces of apple jam have far far more calories than 4 ounces of apples, for example.

However, even if you eat the exact same number of calories of processed foods compared to natural foods, you'll likely still end up with more fat gained with processed foods! The reason for is that most processed foods has undergone transformations that make it far too easy for our bodies to digest quickly and turn into glucose and/or fatty acids. Some of the major reason for that is the removal of natural fiber and water content of foods in the processing.

When we eat, say, a cookie, our system quickly converts it to glucose and this glucose rushes into our bloodstream. Normally blood would deliver it to muscles and organs that could use some new energy. But unless we've been starving for a long time or have been engaging in heavy physical work, we simply don't need that much glucose at the moment! So the extra glucose goes into fat storage.

Compare that to eating, say, a salad with brown rice that has roughly the same number of calories. Because of rich fiber and moisture content of such a meal, the digestion time would be much slower and glucose would be gradually released to the bloodstream and delivered in small doses to the muscles and organs as they need it -- no extra glucose is left to become fat!

This example is, of course, an over-simplification of the millions of complex processes going on in your body. But in principle it is correct. Unfortunately, the vast majority of processed/pre-prepackaged foods are a lot closer to the cookie than to the salad/brown rice which is why you should minimize eating them if you're trying to lose fat.