Sunday, May 6, 2012

Nutrition ABCs...F is for Fat (Part One)

Fat. We love to eat it. We hate it on our backsides. We have tried low fat...and gotten even fatter. We demonized saturated fat and then questioned whether it is really all that bad for us. We have gone gaga for omega 3s but only if they are in the "right" ratio to omega 6s - what is the right ratio, anyway? 

Need the low down on this much-discussed macronutrient? Read on, my on.

Let's start with the basics. What is fat? 

A dietary fat is composed of a glycerol backbone and 3 fatty acid tails. The type of tails determines the structure and function of the fat. If the fatty acids are saturated, they line up nice and snug and are solid at room temperature, like butter and coconut oil. If the fatty acids are missing one little hydrogen molecule, it is called a mono-unsaturated fat. At room temperature, these are liquid fatty acids such as oleic acid, the primary component of olive oil. If there is more than one hydrogen molecule missing, the liquid fat is called poly-unsaturated. These are your omegas. These fats are so "fluid" and flexible that they stay liquid even when cold. Think of flax oil - it doesn't turn solid in the fridge like olive oil does.

What does fat do in our bodies? 

A dietary fat has 9 calories per gram, compared to 4 calories per gram for protein or carbohydrate. It is a concentrated source of energy. When we eat fats, they are digested into fatty acid components so they can be absorbed into the body. Once across the gut, they get repackaged into a molecule called a chylomicron that is transported to the bloodstream so the fatty acids can be carried to cells that need them for energy. And if the cells don't need that energy...the fatty acids travel to fat cells for storage.

We need some fat to help us absorb the fat soluble vitamins A,D,E + K and some of the fat-soluble phytochemicals, such as lycopene in tomatoes. Fatty acids also carry flavour so that we enjoy food more. Fatty acids become incorporated into our cell membranes, which is essentially the bag that holds the cell contents. Eat more saturated fats and your cell membranes will be more saturated. Eat more omega 3 fats and your cells will contain more omega 3s. Fatty acids are also the starting material for cell signalling molecules that can cause muscle contractions or even influence the immune system. 

While fat can contribute to weight gain when consumed in excess, it is really the quality of fats that matter most - not the quantity - when we are talking about good health.

So in my next post, we'll break it down and talk the good, the bad and the ugly.

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