Snapshot series 5: Fats

Fat is familiar to us as a substance we eat in food and store in our body. Both  have the same chemical structure known  as triaclyglycerol (TAG), which, when overconsumed in food, accumulates as body fat  and increases body weight. 

The average 70-kg (155-lb) man has about 15 kg (33 lb) of body  fat, which is equivalent to 140,000 calories or 40 days of stored energy, but only 0.3 kg (10 oz) of stored carbohydrate (900 calories).

 The physical and chemical properties of fats (TAG)  in food are determined by differences in their component fatty acids (FAs), which differ in size and number of carbon double bonds. Saturated fats are mainly derived from animal sources  and are solid at room temperature due to  a lack of double bonds (such as butter),  while monounsaturated fats have one, and polyunsaturated fats have two or more double bonds, which turn these fats into liquid oils.

 These oils can be extracted from plant seeds, including flax, olive and sunflower. The human body can make all but two FAs, namely linoleic acid and alpha-linolenic acid, so these fats must be acquired in our diet and are called ‘essential fatty acids’. 

Fatty acids are used as building blocks for cell membranes in the body and to make hormone-like compounds (eicosanoids) that have metabolic effects essential for life.

Dietary fats are less filling and provide more than twice the energy per gram than carbohydrates and proteins. While most saturated fats come from animal products, one notable exception is coconut oil, which is a highly saturated, hard vegetable fat.