Dietary fat, along with dietary carbohydrates and protein comprise the three macronutrients. Fats have been avoided by dieters over the last 15 years or so due to the factors previously touched upon. Gram for gram, they yield more calories than carbs or protein, they don't take up a lot of room in your stomach so they are easy to over eat and the body is rather efficient at "accessing" the true calorie value from dietary fat. Recall, unlike calories derived from protein which is 80% absorbable or those found in carbohydrates which are roughly 90% absorbable, the calories found in dietary fat are 97% absorbable. Meaning; when 100 calories of fat is consumed, the body "gets" 97 of those.
Historically in the United States, our intake of dietary fat has increased over the last 50 years as has our intake of refined, simple carbohydrates. At the same time, our intake of more natural/complex carbohydrates has decreased and our intake of vegetables has woefully collapsed. That, combined with less physical activity and a more sedentary lifestyle has utterly destroyed our level of health and fitness. For every new health club popping up, there are a hundred little kids, fat and overweight.
When dietary fat is consumed, the body can't transport the whole shabang about the blood. Food fat has to be broken down into its raw components, fatty acids and glycerol. Fatty acids provide fuel for resting muscles and during aerobic work and glycerol can be, through a long chain of events, "re- manufactured" into glucose. This glucose can influence, to a small degree, the total amount of glucose in the blood.
The body fat storing mechanisms in the body rely on total calories to make new body fat and the inter-dynamic relationship between dietary fat and insulin produced from carbohydrates. While insulin has the potential to store carbs as glycogen or to shoot them off towards fat cells influencing the accumulation of body fat, and to release lipoprotein lipase which essentially blocks fat cells from breaking down, it's strongest influence in the accumulation of added body fat lies in its ability to stimulate the uptake of dietary fat by fat cells. In a nutshell, a high dietary fat intake in the presence of insulin virtually guarantees dietary fat will not only "make it" to fat cells, but quickly be packed away to make bigger fat cells. Just as insulin is the "trigger" that sets in motion the removal of glucose from the blood and into glycogen or fat, it's the main trigger that allows fat cells to "open up" and allow additional dietary fat to be packed away. The deadly combo: simple sugars or a massive amount of complex carbohydrates and dietary fat.
INSULIN + Dietary Fat = Body Fat
In both cases, elevated insulin escorts fatty acids into fat cells making you fatter. Once there, the fat stays there as elevated insulin "locks and seals" fat cells up making it harder for the body to draw upon them as fuel.
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