Why does the body need fat?

Factual Questions
1

Just came from a meeting with a nutritionist who is book wise, but could not answer questions outside the text. Like, she states a healthy diet is 50% carbs, 20% protein, and 30% fat (ideally, mono- and polyunsaturated).

But, why is 30% fat, or any fat, needed in a diet? She couldn’t answer about why this is necessary…when you’d think you’d want it even lower! Is this strictly a physiological requirement, or perhaps a psychological requirement? The latter being a sanity check for those (the majority?) who probably couldn’t stick to a stricter regiment of less than that?

Don’t understand the thinking here. As a bonus, why should carbs be so high? I WAG that since all foods (in excess) can hurt the body, perhaps the carbs are most easily controlled by a healthy indivdual with exercise…so it may be seen as the lesser of all evils? And, good news to dieters as these are the “comfort foods” from which most people used to break their diets (from old school thinking).

  • Jinx
2

Read this and see if it helps out.

3

Some vitamins are fat soluble so a certain amount may be needed to get them but 30% sounds awfully high. When I worked at biosphere 2 I remember Dr. Walford talking about how the crew inside had a difficult time getting eough fat in their diets but in their case meat was an extremely rare at meals and many of the plants didn’t provide much fat. I think most of them would have been happy to never see another banana again in their lives when they finished the two year experiment.

4

Warning: I’m not a nutritionist, but I’ve been learning a lot about nutrition lately, so here goes.

First of all, you need to get a certain amount of energy from food. Energy can come from fats, proteins, and carbohydrates.

Your body needs a certain level of fat, because important parts of you (your cell walls and most of your brain) are made of fat. Fat is made of building blocks called fatty acids, and your body needs those building blocks to assemble the different fats it needs to grow and repair tissues. Another reason to consume a reasonable level of fat is to get fat-soluable vitamins. If you cut back too far on fat (I’m not sure how far) you’ll need to take vitamin supplements. You can cut your fat calories down to 10%, safely, but for most people, 30% is a much more comfortable level, as you say. Humans have been programmed by evolution to crave fat because we’ve spent most of our history taking in too few calories, not too many. If you choose leaves you feeling deprived and unhappy, you are much more likely to go back to your old eating habits.

Your body also needs proteins to build and repair tissue. The building blocks are amino acids. Now, your body can make many types of amino acids from other raw materials, but there are 8 or 9 (depending on who you ask) amino acids that you need to get from the foods you eat. So you also need a certain amount of protein in your diet.

That leaves carbs, which fill out the rest of the calories that you need for energy. One of the reasons carbs make a good “filler” is that they are not as energy-dense as protein or fat, so eating carb-rich foods will leave you feeling more full, without consuming as many calories. Of course, if you choose the right carb-rich foods, they’ll also bring alot of healthy stuff along with the energy: water-soluable vitamins, fiber, antioxidants, etc.

I track what I eat kinda obsessively with fitday.com, and ('cause I’m sure you’re dying to know) I get 28% of my calories from fat, 17% from protein, and 55% from carbs, which took a long time (about 2 months!) to get used to, but now I’m pretty happy with it, partly because my body and psychology has adjusted to it, and partly because I’ve learned what foods are healthy and satisfying, what foods to avoid 'cause they’re not too good for the diet and they don’t give me enough satisfaction to be worth it, and what foods I can enjoy in moderate amounts.

5

“If you choose a diet that leaves you feeling deprived and unhappy, you are much more likely to go back to your old eating habits,” I mean. I swear those words were there when I previewed!

6

Are you asking a biochemistry question Jinx, like just what is the point of fat? Its one of the basic building blocks of life, along with proteins, carbohydrates and nucleic acids (DNA and RNA). Fats play many, many roles in phsiology; they’re important structurally (phospholipids in cell membranes), as highly concentrated energy sources, in signalling as intracellular messengers etc. they have a million and one uses. I would WAG that no lifeform higher than a virus could exist without fats playing a role in its metabolism/physiology somewhere.

If your question is more nutritional, like you get all of that but don’t see why we have to eat them, then I guess I don’t know either. The pathway that the body uses to build fatty acids is very well understood, it starts off with simple, small carbon building blocks that condense again and again to make the large fatty acid molecules, which are themselves components of fat. The pathways that break down the fats we eat are also well-understood. How much dietary fat we need to throw into this lipid metabolism to meet its various demands is the question. Sorry , don’t knowthe answer! Less than I eat for sure.