Have you ever asked why do we not gain muscle instead of fat? That would be wonderful, wouldn’t it? Eat a lot of protein and start looking like a bodybuilder!
To understand why we gain fat, we need to understand how our bodies are built. Recall from our biology class that we use carbohydrates from food to give us instant energy. The carbs we eat are transformed into glycogen in our muscles and kept there for a very short period of time till we need it as we move about. Proteins on the other hand, are broken down into amino acids and then selectively reabsorbed, as much as the body needs to recreate muscles. No protein or carb is kept in some locker in our body. Excess proteins are processed in the liver and shed.
The only nutrient source that the body has evolved to store is fat. Why? Because it is the densest fuel to carry! Even the smallest amount of fat can be used for a long time.
The second reason we store fat, is that our current bodies evolved about 200,000 years ago and at that time we needed to quickly “suck up” the fats from foods we ate. Fat digestion is quite elementary — break it down into smaller chunks by using some chemicals (enzymes) and then use bile salts to quickly move the smaller fat globules straight to our storage depots. Look at the image on the right. All you see is a big fat globule being split up and absorbed by the cells (at the bottom); that is it. Not too many steps there. When our ancestors roamed the savanna and found bone marrow or animal skin laden with fat, we found it is best to absorb it quickly for we never knew when we’d get the next meal. It may be after a day, or two, or maybe a week! This is when the fat could be brought out and used as an energy source.
Things are quite different now but unfortunately, we have to still use the body from 200,000 years ago! We live in a world where food is abundant and starving is pretty much out of the question for most of us. Therefore, we need to be aware of this super efficient fat magnet of a body we have.
Speaking of efficiency, have you wondered how little energy we need to absorb fat? This might come as a shock to many, but the number is only around 3%! Which means that if we ate the potato chip on the left, our body would burn that small crumb on the top right corner, and store the fat from the rest 97% of that chip neatly on our mid section, thighs, buttocks, back, etc. There! Now you know how we have those fat deposits in our body.
In order for the triglyceride to be absorbed, large aggregates of dietary triglyceride must be emulsified and then they must be enzymatically digested. Pancreatic lipase and bile acids are the key components of this transformation and absorption.