Can We Make Fat?

While diet-derived fat is being deposited in tissue throughout the body, if a lot of carbohydrate and/or protein were consumed, some can be converted to fat. This takes place in the liver and fat cells, with the latter only able to use glucose to make fat. Insulin promotes this activity, which makes sense since diet-derived carbohydrate and some amino acids raise insulin levels. The principle fatty acid products are palmitic acid (16:0) and oleic acid (18:1 ω-9) and palmoleic acid (16:1 ω-9). The fat made in fat cells is stored within those cells, while the fat made in the liver is packaged up and relocated mostly to fat cells for storage.

Contrary to popular belief the ability of the body to make fat from excessive dietary carbohydrate and protein is not as strong as once thought. However it does occur and for some people and situations, such as long-term excessive calorie intake, the involved processes are stronger. On the other hand, deriving more fat from polyunsaturated fat sources such as plant and fish oils can reduce these processes.

While fat manufacturing from diet-derived energy building blocks such as carbohydrates (glucose and fructose) and protein (some amino acids) does occur, it only explains a portion of the accumulated body fat during weight gain. The majority of the fat accumulated is from the diet. Since fat is mostly consumed with carbohydrate and protein, both of which raise insulin levels, more dietary fat is directed to storage. Since too many total calories are being consumed more fat will be directed into storage than broken down for use as fuel. Thus there is a net gain of body fat which in turn increases body weight.