Does food fat make you fat?

Question
A friend and I are having a debate about whether calories from fat are more likely to increase a person's weight than calories from other sources (carbs, sugars, etc.)

One of our hypotheses is that the body can add an ingested fat molecule directly to your body's fat, so that eating fat makes you fatter. The other hypothesis is that the body has to break down a fat molecule first and that then, if there is an excess of calories in the system, the body creates fat from the excess calories.

Which one is right or are we both off?  We are not considering other problems with fat, such as cholesterol - only the effect on one's weight.

Answer
Hi Terry

Thank you for such a good question :)

That's right that "the body has to break down a fat molecule first" but this is true for any fuel the body uses, carbohydrates including.

Carbohydrate is the source of energy the body prefers, this is why we are so addicted to sweet taste. However, when there's little or no carbohydrates, the body eventually switch to running on by-products of fat metabolism, ketone bodies. Once the state of ketosis is established, one good thing happens: the body starts considering its own fat as legitimate fuel and doesn't get into the hungry mode for as long as there's enough fat to metabolize and use for energy, from food or from body's fat depots.

To achieve and maintain the state of ketosis, one has to consume roughly two times more fat than carbs and protein combined.

Another interesting thing about low carb, high fat diets is, as a clinical research showed, that people on these diets can eat up to 300 Calories a day more than their fellows on low fat high carb diet and still lose more weight.

Read more:

The Body's Fuel
http://bestlowcarbs.com/fat_burning_index/2006/06/what-is-fat-burning-index.html

Calorie Intake On Atkins and Low Carb Diets (3 studies)
http://www.dietandbody.com/articles/article1100.html

Fat burning Rate Increases With the Increase of the Anti-insulin Index
http://dietandbody.com/metabolic_syndrome/?page_id=8

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