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I often hear from many people saying to waiters - "Please, don't put oil to salad". They probably believe the fat from vegetables has the same impact on the weight as an "animal" fat (meat, eggs, butter).

My questions are -

  1. Are these two types of fat have equal influence considering their converting to fat tissue in humans?

  2. What are the pathways for conversion of vegetable oil fats to adipose tissue storage, in humans?

  3. If one eats $X$ grams of either saturated or unsaturated fats, will they (in equal conditions) gain equal weight ($Y$ grams) in both the cases ?

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migrated from Apr 29 '14 at 20:56

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There is a subtle difference between oils and fats- oils are generally unsaturated (Carbon-Carbon double bonds) whereas fats are saturated (all single bonds).

Are these two types of fat have equal influence considering their converting to fat tissue in humans?

No. There are some kinds of fatty acids that are synthesized only by plants (Essential fatty acids). However, these can be obtained indirectly from animal sources such as fish.

Fats have multiple roles- not just storage. They are also critical for making up the cell membrane.

What are the converting pathways for vegetable oil fats to adipose tissue in humans?

The fatty acids in oils are absorbed in the intestine and esterified (wit glycerol) to form triglycerides. Then, they are incoporated in lipoprotein complexes. There are different types of lipoproteins- VLDL (Very Low Density Lipoprotein), LDL (Low Density Lipoprotein) and HDL (High Density Lipoprotein) which have different sizes and compositions.

When lipoprotein comes in contact with lipoprotein lipase in capillaries, the free fatty acids are liberated from trigycerides, which is taken up by adipose tissue.

The fats stored in adipose tissue depends on diet. This has been studied in rabbit but similar principles may apply to humans too. Fats can also be synthesized in the body. It is always saturated fat and is synthesized by the fatty acid synthase complex. The starting substance is Acetyl-CoA which is produced during catabolism of both carbohydrates and fats.

if one eat Y of 2 meal if saturated and unsaturated fats, he/she (in equal conditions) will gain X gram if they were saturated fat and Z in a case of unsaturated fats?

By principles of mass balance, if both have equal rates of absorption and degradation then there will be equal gain. According to this study, absorption rate of unsaturated fats is higher. In that case if you eat $X$ grams of both types then the absorbed amount should be $Y_{sat}$ < $Y_{unsat}$

I am not sure about the degradation rates but I think it is higher for saturated fats because unsaturated has to be reduced to saturated before metabolizing via $\beta$-oxidation. Determining the exact steady state values will be tricky without a mathematical model.

NOTE: Dont confuse this with body weight gain (in the sense of obesity); it is a complex phenomenon. You have to consider a lot of things when predicting weight gain.

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Do you know any answer to question if one eat Y of fats, he/she (in equal conditions) will gain X gram if they were saturated fat and Z gram if they were polyunsaturated fats? – Ilan Apr 30 '14 at 5:15
Gaining in the sense ? – WYSIWYG Apr 30 '14 at 5:38
Weight i mean - are these two types of fat similar considering weight gain – Ilan Apr 30 '14 at 5:46
weight gain is a complex issue. it is not that straightforward. I added an answer to that question but it is in the sense of amount absorbed in the body. – WYSIWYG Apr 30 '14 at 5:47

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