Educational Series
The Science of Nutrition.
Importance of Fat in the Diet
By Mohammad Ahrar, PhD
Introduction
Fats, carbohydrates, proteins, vitamins, minerals, and water are substances the body needs for health and normal growth. These nutrients have previously been discussed in several issues of Peyk (Peyk ##159-175). This article highlights the importance of fat in the diet and the pros and cons of consumption of different types of fats.
Why do you need fat in your diet?
The reasons that humans need fat are summarized below:
- Fats and lipids provide twice as much energy as carbohydrates and proteins.
- The brain is mainly made of fat. The myelin sheath that covers the axon of most nerve cells is made of lipids.
- The membranes of all cells in the body are made up of lipids (mainly phospholipids). Without these molecules, cells cannot function and organisms cannot survive.
- Fats are necessary for absorption of fat-soluble vitamins, such as vitamins A, D, E, and K. Without fat in the diet, the absorption of these vitamins would be in jeopardy.
- Females with abnormally low body fat may have problems with fertility.
- Fats insulate the body and support and cushion all organs of the body.
What are fats and oils made of?
Fats are usually of animal origin and normally are solid at room temperature. Oils are of plant origin, mostly liquid. Fats and oils are made of two components—fatty acids (made of a chain of carbon atoms) and glycerol (a three-carbon alcohol). When 3 fatty acids are attached to a glycerol, the compound is called a triglyceride or neutral fat. Most fats in animals and human bodies are in the form of triglycerides.
Types of fats in foods
Fats can vary based on the composition of their fatty acids and the presence of minerals and other molecules. Saturated fatty acids contain chains of carbon that are completely bound with hydrogen ions (saturated with hydrogen). When most of the fatty acids in a fat are saturated, the fat is known as saturated fat. Most fats from animal sources such as fatty meat, milk fat, and eggs are mainly saturated fat. If one or more of the carbons in a fatty acid chain is (are) not fully bound with hydrogen atoms, the compound is considered unsaturated fat. Most plant-based oils, such as olive oil, corn oil, and sunflower seed oil, contain large proportions of unsaturated fatty acids.
Absorption of fats in the digestive system
When you eat fat, it is broken down into smaller globules by your bile and then digested by pancreatic and intestinal enzymes into simple compounds, namely glycerol and fatty acids. The absorbed fatty acids and glycerol will be used to produce energy, will be converted to other compounds, or will be stored as fat in some tissues. Metabolism of lipids occurs in the liver, as well as in other organs of the body. The liver produces more than 70% of cholesterol and a variety of fats that the body needs for different purposes, such as the formation of steroid hormones and conversion to other compounds.
Are saturated fats harmful to the body?
Consumption of saturated fats and their effects on human health is very controversial. Some medical studies indicate that moderate consumption of saturated fats do not raise the risk of heart disease. (3) Other reports indicate that saturated fats increase Low Density Lipoproteins (LDL, so called bad cholesterol), but unsaturated fats increase High-Density Lipoprotein (HDL, so called good cholesterol). Therefore, they can increase the risk of Coronary Heart Disease (CHD).
Note: Most fats and oils contain both saturated as well as unsaturated fatty acids. For example, olive oil contains 14% saturated fatty acids and 86% unsaturated fatty acids. Butter contains 64% saturated fatty acid and 36% unsaturated fatty acids. Coconut oils contain 86.5% saturated fatty acids. More information about fats is explained in Peyk #159.
Safe storage of fats and oils
Fats and oils that contain a large percentage of unsaturated fatty acids are more vulnerable to oxidation and rancidity. For example, oils such as corn oil, canola oil, olive oil, and some other types of oils should be kept in dark containers, away from direct light and in cool temperatures. Containers made of copper and iron oxidize fats and oils and should not be used to keep oils and fats.
Do saturated fats have any advantages?
Saturated fats have good use in industry. They are more tolerant of oxidation and have a longer shelf life compared with unsaturated fats. Most commercially-prepared foods, such as cookies and cakes on grocery store shelves (not refrigerated), use saturated fats.
Health benefits of unsaturated fats in the diet
Unsaturated fats are considered beneficial fats because most studies have shown that they can improve blood cholesterol levels, ease inflammation, stabilize heart rhythms, and play a number of other beneficial roles. Unsaturated fats are predominantly found in foods from plants such as vegetable oils, nuts, and seeds. Some fatty acids, such as Omega-3 and Omega-6 fatty acids, are considered essential because the body can’t make them, so they must come from food. Studies have shown that lipids that contain both Omega-3 and Omega-6 fatty acids are essential for healthy brain function, normal eyesight, healthy nerve cells in growing embryos, and are required for maintenance of normal brain function and learning ability in adults.
Sources of unsaturated fats
Monounsaturated fatty acids are found in high concentrations in olives, avocados, peanuts, nuts such as almonds, hazelnuts, and pecans, pumpkin seeds, sesame seeds, and canola oils.Polyunsaturated fatty acids include Omega-3 and Omega-6 fatty acids. They are found in high concentrations in plant sources as well as in some animal sources.
Animal products high in Omega-3 fatty acids include cold-water fish such as salmon, herring, mackerel, tuna, anchovies, and sardines. Egg yolk from hens fed alfalfa is also a good source of Omega-3 fatty acids.
Plant sources of Omega-3 fatty acids include chia seeds, flax seeds (linseed), walnuts, hemp seed, rapeseed oil (canola oil), sunflower seeds, corn, soybeans, and some other plant seeds. (For more information about Omega-3 and Omega-6 fatty acids, please visit Peyk #160.)
Is burning fats and oils harmful?
Carbohydrates are a quick source of energy. One gram of carbohydrate provides about 4 kilocalories, whereas one gram of fat produces about 9 kilocalories. Fats take longer to metabolize and release energy. Excess fat in the diet produces extra calories and if you are not burning the extra calories during physical activity, the extra calories can be stored as fat.
Energy from fats vs energy from carbohydrates
The carbohydrate situation may be more serious. When sugary foods are consumed, they will be converted into simple sugars such as glucose and fructose. (See discussion in Peyk #165.) Glucose activates the pancreas to secrete insulin, and insulin is known as a fat-making hormone. It activates millions of adipocytes (fat cells) in the body to convert glucose to fat, rather than burning it as calories. Fructose also plays its part in fat formation. The intermediates of fructose metabolism in the cells are primarily directed toward triglyceride synthesis, which is the major cause of weight gain.
Are trans fats healthy?
Trans fats are made by heating liquid vegetable oils in the presence of hydrogen gas and some catalysts to make saturated fats such as margarine and shortenings. These partially hydrogenated oils stay solid at room temperature and are less likely to become rancid. They can withstand heating without breaking down, making them ideal for frying in fast food restaurants and the food industry. However, medical studies have shown that trans fats are not the best choice of fat for daily consumption because they raise bad LDL and lower good HDL, contribute to insulin resistance, and they create inflammation which has been implicated in heart disease, stroke, diabetes, and other chronic conditions.
Dietary guidelines for fat consumption
A – Saturated fat consumption: The Centers for Disease Control and Prevention (CDC), recommends consuming less than 10% of daily calories as saturated fats. As an example, if your total calories needed for 24 hours is 2000 Cal, about 200 calories (10%) can be from saturated fats. If you divide 200 by 9 (Calories produced by 1 gram fat = 9), then the amount of total saturated fat consumption allowed in 24 hours would be about 22 grams.
B – Total fat consumption: The recommendation for total fat consumption in a day is between 20 to 35% of calorie intake, mostly from unsaturated fat. That is about 44 to 77 grams of total fat per day from a variety of foods. The average fat intake in the U.S. is between 100 to 150 grams per day.
Summary
Fats are an essential part of the diet and must be included in the daily food intake for its role in a healthy brain and other organs of the body. While saturated fats may not be as harmful as once thought, evidence clearly shows that unsaturated fat remains the healthiest type of fat. Polyunsaturated fatty acids, such as Omega-3 and Omega-6 fatty acids, are essential for health and should be included in the diet. They are found in high concentrations in plant sources as well as in some animal sources. Trans fats are not the best choice of fat for daily consumption.
References
1- Nutrition and Diet Therapy: Evidence-Based Applications, 4th Ed., Lutz, Carroll and Przytulski K., F. A. Davis Company, Philadelphia (2006).
2- Emissions of volatile aldehydes from heated cooking oils, Katragadda, H.R., et. al., Food Chemistry 120 (1), pp. 59-65 (2010).
3- https://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/fats-and- cholesterol/types-of-fat/
4- https://www.cdc.gov/nutritionreport/pdf/Second-Nutrition-Report-Fatty- Acids-Factsheet.pdf
5- https://www.cdc.gov/pcd/issues/2019/19_0121.htm
