What's The Skinny on Fat?

Fat is probably the most feared and misunderstood macro-nutrient. It has been associated with heart disease and conjures up images of going directly from the lips to the hips. Here's the latest skinny and science on fat. Fat misconceptions emerge from the notion that fat from foods is inherently fattening. Fat, like carbs and protein, is a source of energy (calories). Calories are a measure of food energy and are expressed in kilocalories or kilojoules, or more simply “calories”.


The breakout for the macronutrients are:
Protein – 4 cal/gram
Carbohydrate – 4 cal/gram
Fat – 9 cal/gram
Alcohol – 7 cal/gram

As you can see, fat has more calories per gram, but there are many factors that determine if a food (or fat) will be stored as fat. These include how foods are metabolized, the quality and composition of one’s diet, and what type of exercise a person does.
In order to sort through the misinformation and myths surrounding fat we need to understand a bit about the biochemistry and role of fat.

Biochemistry 101: Important Fat Functions
    1    Energy
    2    Protection
    3    Body temp regulation
    4    Nutrient transport
    5    Regulates stomach emptying
    6    Hormone synthesis
    7    Palatability and satiety

Fat Digestion, Transport, Storage and Metabolism: 
Fat digestion begins in the mouth and stomach, but primarily occurs in the small intestine through the action of bile salts released by the gallbladder, along with enzymes released from the pancreas.

Fats are transported by structures called chylomicrons: HDL (high-density lipoproteins), LDL (low-density lipoproteins), apolipoproteins and lipoprotein(a). HDL is cardioprotective, but LDL, apolipoproteins and lipoprotein (a) have been correlated with heart disease.

Fat is primarily stored as “white fat”, which is metabolically inactive and more prevalent as we age. Brown adipose tissue (BAT) is another way fat is stored. BAT is more metabolically active. Fat metabolism is regulated by insulin, thyroid hormones, glucocorticoids, catecholamines and growth hormone.

The fat in our food is made up of fatty acids, which are classified into three major groups based on their chemical configurations:
 
    1    Saturated
    2    Monounsaturated
    3    Polyunsaturated

All fatty acids are made up of a chain of carbon atoms with hydrogen atoms filling in the spaces around each carbon atom. The configuration of these atoms determines the type and nature of the fat and whether it is a solid or liquid at room temperature. In addition, it also determines the stability of a fat, which has implications for health and culinary purposes. In general, all fats and oils from animal and plant sources are made up of a combination of saturated, monounsaturated and polyunsaturated fatty acids.

Saturated Fatty Acids: 
Due to their tight chemical bonding, saturated fatty acids are solid structures that are extremely stable and have a high melting point. Saturated fatty acids are found mainly in animal fats like dairy, red meat, and the fat on poultry, as well as in tropical oils like coconut oil. Additionally, the body makes some of its saturated fatty acids from carbohydrates in the diet.

In the past, saturated fat was thought to be linked to heart disease and stroke, but it turns out that this may have been a big, fat lie. A 2010 meta-analysis published in the American Journal of Clinical Nutrition pooled together data from 21 studies and included almost 350,000 people tracked for an average of 14 years. This study concluded that there is no relationship between the intake of saturated fat and the incidence of heart disease or stroke.

Monounsaturated Fatty Acids: 
Because of the looser chemical bonding of monounsaturated fats, they are usually liquid at room temperature. Monounsaturated fats are relatively stable, even when exposed to some heat. The most common type of monounsaturated fatty acid found in food is called oleic acid. Monounsaturated fatty acids are found in olive oil, avocados, macadamia nuts, peanuts, almonds, pecans, and cashews.