Saturated fats are fats that are mainly found in animal fats. Trans fats are usually fats that are produced when a product goes through hydrogenation(adding of hydrogen) or in other words, processed food. Saturated fats if eaten moderately, does no harm to your body and your body can convert it into energy. On the other side, you should avoid trans fat as much as possible because it harms your cardiovascular system without giving your body any benefit. One thing to note, trans fat is actually a type of unsaturated fat, the 'trans' actually tells you the structure of the fat, it's one of the geometrical isomers. Besides, saturated fats increase LDL and unsaturated fats increase HDL where HDL helps your body to eliminate LDL.

To lower down your cholesterol level:
Do more exercise like HIIT, cardio with compound exercise and etc -to lose body fats and increase metabolic rate (from muscle growth), not to mention if you have more muscles, you're less likely to be fat again thanks to your higher BMR(resting metabolic rate);
Cut your saturated fat intake and eat more unsaturated fats (fats from plants/nuts) and fibre (veggies and fruits)-to maintain the HDL/LDL balance and fibre inhibits the absorption of cholesterol from food;
Keep your waist size below 40" if you're male and 35" if you're female, this is more accurate compared to using BMI, this is because it's proposed that waist size above 40"/35" is prone to diabetes and other chronic diseases;
Have efficient sleep (the type of sleep where you wake up energetically, not feeling tired at all).

It's weird to hear your doctor doesn't recommend you to eat fish oil supplement because fish oil supplement consists of polyunsaturated fats not saturated fats, maybe your doctor is worried that you might overconsume it or hopes you get them from meals instead. This is because there are still unknown factors (nutrition that we haven't discovered) in meals which are beneficial to our bodies.

If you really can't differentiate, you can always read nutrition facts on the food(mainly the ingredient of the dish) that you wanna know its content. As for french fries, I think as long as you deep fry them yourself, the trans fat is literally negligible. The problem with deep-frying food outside is that they keep reusing the oil which already has trans fat in it and it will keep increasing because heat energy promotes reaction(hydrogenation) in the molecules to stabilise themselves. So if you really crave for food like french fries, just deep fry it yourself with new cooking oil every time. You may reuse the oil 1-2 times but more than that is strictly not recommended.

One way to roughly guess whether a dish has trans fat or not is to see the cooking method itself involves high temperature or not and how many times the cooking oil is used. So from these 2 principles, you can tell stir-frying food and deep-frying food have trans fats but not that much(or negligible) unless the cooking oil used is reused many times already.

This post has been edited by Yenactiet: Jun 1 2020, 09:53 AM

Whenever the cooking oil is heated, be it new cooking oil or reused oil, trans fat will be produced gradually from a reaction called hydrogenation. And, high temperature will increase the rate of this reaction as the molecules of the cooking oil have more energy to attach to the hydrogen atoms in the oil to stabilise themselves. If you use new cooking oil or oil that has been re-used once or twice, the trans fat produced in it is not that much to the point it harms your body because even the 'boosted' rate is still slow, so it's considered as negligible. Whatever inside the cooking oil will stick to the dish you're preparing, so your dish will have trans fat too, it's the amount of trans fat that matters.

edit: The type of cooking oils you use also matters. One of the healthiest cooking oil is peanut oil. You can literally use peanut oil for every cooking method as it has a very high smoking point and high in unsaturated fats. If you want the healthiest cooking oil, it'd be sunflower oil with high oleic, but I believe it's also one of the most expensive cooking oil.

From this table, you should pick the cooking oil that has high monounsaturated fats or high saturated fats for frying method(deep or stir), of course, the preferred cooking oil would be the one that has high monounsaturated fats.

This post has been edited by Yenactiet: Jun 2 2020, 12:39 AM

You're most welcome. But I wanna add one point, aside from high monounsaturated fats, you have to pick cooking oil that has a high smoking point also for frying method. This is because if the cooking oil is heated past the smoking point, its structure will be affected and destabilised. If you reuse such oil, the trans fat will be formed faster too due to the lesser amount of monounsaturated fats/saturated fats in the oil. Monounsaturated fats and saturated fats are stable compounds, this is why it's recommended to pick cooking oil that is rich with either of them and has a high smoking point for frying purpose.

In case you're or any reader that's wondering about the isomers, there are two types of geometric isomers, cis- and trans-. cis- unsaturated fats are the good fats that are recommended to take more and trans fats are the worst fats(even worse than saturated fats). Take a look at pictures below.

The left compound is a cis- compound and the right is trans-. As you've heard of like charges repel and opposite charges attract, the same thing works here. The Cl-Cl will repel each other so it takes more energy for the compound to overcome the force, this is called steric effects. This is why some of the cis- unsaturated fats will turn into trans fat after going through partial hydrogenation, it simply takes less energy for them to maintain this form. And nobody in this world likes to spend more energy than needed.

This post has been edited by Yenactiet: Jun 3 2020, 11:29 AM