Dietary fats: what functions do they serve in the body?

Dietary fats and oils are important components of human diet, providing energy (fats are the densest source of calories) and essential fatty acids and serving as a source of fat-soluble vitamins (vitamins A, D, E, and K). Fats improve texture and palatability of foods and have an important role in inducing satiety as well.

But, fat is high in calories and small amounts can add up quickly and you may end up gaining weight if you do not keep your fat intake in check

Fats in diet come from two sources:

  1. Visible fat: oils and fats used for cooking; oils are fats that are liquid at room temperature
  2. Invisible fat: present in almost every food item; nearly one third to half of all fat in typical Indian diet is invisible fat

The nutritional and health effects of dietary fats are determined by the nature of their constituent Fatty Acids or FAs (which make more than >95% of fats/oils) and the composition of minor components called ‘nonglyceride components'(<5%)’

Fatty acids are of the following types:

  1. Saturated Fatty Acids (SFAs)
  2. Monounsaturated Fatty Acids (MUFAs)
  3. Polyunsaturated Fatty Acids (PUFAs): PUFAs  are two types
    • N 3 or omega 3 PUFAs such as Alpha- Linolenic Acid(ALA)
    • N 6 or omega 6 PUFAs such as Linoleic Acid (LA)
    • Linoleic acid [LA] and a-linolenic acid [ALA] are essential fats, meaning the body cannot produce these PUFAs and they have to come from diet
  4. Trans Fatty Acids (Trans FAs): these are found in very small quantities in natural oils but in high quantities in partially or fully hydrogenated vegetable oils (vanaspati, margarine, PHVO)
  5.  Cholesterol: it is ONLY found in fats of animal origin such as ghee, butter, charbi, lard, shortening etc.  ALL vegetable oils are FREE of cholesterol.

The most important consideration regarding fat intake is not how much fat, but what type of fat you eat; you can eat high amount of fat (even up to  35%of total calories), provided you keep your calorie intake equal to your requirement AND eat right types of fat (good fats)

What are good fats and bad fats?

Bad fats are the ones that increase our risk of atherosclerotic disease by increasing the level of bad cholesterol in the blood, whereas good fats help in keeping the level of cholesterol in check.

Bad Fats:

Trans FAs are the worst of bad fats, the number two spot goes to SFAs and third spot to cholesterol present in diet

Trans Fatty Acids (Trans FAs): 

  • Consumption of Trans FA is to be kept at less than 1% of total calorie intake
  • Excessive intakes of Trans FA, especially synthetically produced Trans FA, not only increases LDL but also decreases HDL and raises the risk of atherosclerosis and heart disease
  • Synthetic Trans FAs are found in partially hydrogenated oils/fats used to make fast foods, baked products and snacks (partial hydrogenation adds shelf life and reduces need for refrigeration)
  • Check food tables in packaged foods, margarine, vanaspati etc. for Trans FA content and also find out, if possible, what fat does your favorite fast food joint use

Saturated Fatty Acids (SFAs):

Adults, and even children are advised to keep their SFA intake such that it contributes less than 10% of total calories consumed

  • Excessive intake of SFAs (more than 10% of total calories) leads to higher level of LDL and total cholesterol and increases the risk of heart disease and its complications
  • People who have high BP or high blood cholesterol are advised to have even lesser amount of SFAs (less than 6-7% of total calories)
  • SFAs are found in high levels in food of animal origin: milk, eggs, meats, liver etc. and animal fats (butter, ghee etc.). The SFA content of vegetable oil varies; coconut and palm oil contain high amounts whereas the rest of them contain low to medium amount
  • Replacing SFAs in diet with other fats (MUFAs and PUFAs) lowers blood cholesterol and risk of heart diseases
  • Some recent studies are touted to have found no concrete evidence between SFA intake and risk of heart disease, however the actual findings are given below:
    • One meta-analysis of 21 studies said that there was not enough evidence to conclude that saturated fat increases the risk of heart disease, but that replacing saturated fat with polyunsaturated fat may indeed reduce risk of heart disease
    • Two other major studies concluded that replacing saturated fat with polyunsaturated fats like vegetable oils or high-fiber carbohydrates is the best bet for reducing the risk of heart disease, but replacing saturated fat with highly processed carbohydrates could do the opposite


  • Limit of cholesterol consumption/day is 300 mg for healthy adults, but for people with high cholesterol, keeping dietary cholesterol intake lower than 200 mg/day has been shown to lower blood cholesterol  by  3-5% over and above other measures
  • Dietary cholesterol raises the cholesterol level in blood—but not as much as SFAs. Thus SFAs and not dietary cholesterol is the primary target of control or restraint. However, the two often are found in the same foods. So by limiting your intake of foods rich in saturated fat, you will also help reduce your intake of cholesterol
  • Eggs and shrimps have disproportionately high level of cholesterol but not so much SFAs (especially shrimps); restriction on consumption of eggs and shrimps are much debated but , some experts say that people with normal blood cholesterol should consume them liberally because their benefits (proteins and vitamins in eggs, and additionally omega 3 FAs in shrimps ) outweigh the risk

Good Fats: Mono Unsaturated Fatty Acids (MUFA) and Poly Unsaturated Fatty Acids (PUFA) are considered good fats

PUFAs: are essential fatty acids, which have to be obtained from diet as such since body can not make these on its own.  Polyunsaturated fats are used to build cell membranes and the covering of nerves. They are needed for blood clotting, muscle movement, and inflammation

Eating polyunsaturated fats in place of saturated fats or highly refined carbohydrates reduces harmful LDL cholesterol and improves the cholesterol profile. It also lowers triglycerides thus improving your heart risk profile

However, there is a debate going on in nutrition community about how much PUFAs should be consumed, since very high intake of PUFA is being linked with heart risks as well; experts recommend to keep PUFA intake between 6-11% of total calorie input


MUFAs  are the best ‘good fats’; there is no restriction or upper limit on the consumption of MUFAS. MUFAs have been found to be heart protective and are touted as the protective factor in Mediterranean diet. MUFAs along with PUFAs should replace the SFAs and Trans FAs in your diet as much as possible

Good source of MUFAs are olive oil, canola/mustard oil , groundnut oil and nuts

Read more to know about how to chose oils for cooking, such that you adhere to all the recommendations regarding oils for cooking

Also check out: Family oil use calculator to find out whether your family is consuming oil in right amount or getting too much of it

CHECK OUT: Our references for recommendations on diet