Fats are an important part of food science because they affect energy, cell structure, flavor, texture, and long term health. In nutrition, the word fat usually refers to lipids, a group of molecules that do not mix well with water. Students often hear that fats are either good or bad, but the science is more specific.
The type of fat, the amount eaten, and the overall food pattern all matter.
Key Facts
- Fat provides about 9 kcal per gram, while carbohydrates and proteins provide about 4 kcal per gram.
- Most dietary fat is in the form of triglycerides, made of 1 glycerol molecule and 3 fatty acids.
- Saturated fatty acids have no carbon carbon double bonds, while unsaturated fatty acids have at least one carbon carbon double bond.
- Energy from fat can be estimated with E = 9 kcal/g x grams of fat.
- Percent of calories from fat can be calculated with percent = fat calories / total calories x 100.
- Essential fatty acids, including omega 3 and omega 6 fats, must come from food because the body cannot make enough of them.
Vocabulary
- Lipid
- A lipid is a biological molecule that is mostly nonpolar and does not dissolve well in water.
- Triglyceride
- A triglyceride is a fat molecule made from one glycerol backbone attached to three fatty acid chains.
- Saturated fat
- A saturated fat contains fatty acid chains with no carbon carbon double bonds and is often solid at room temperature.
- Unsaturated fat
- An unsaturated fat contains one or more carbon carbon double bonds and is often liquid at room temperature.
- Emulsifier
- An emulsifier is a substance that helps fats and water mix more evenly, such as lecithin in egg yolk.
Common Mistakes to Avoid
- Calling all fats unhealthy is wrong because the body needs fats for cell membranes, hormones, brain function, and absorption of vitamins A, D, E, and K.
- Ignoring serving size is wrong because fat is energy dense, so a small amount can add many calories to a meal.
- Thinking cholesterol and triglycerides are the same is wrong because cholesterol is a steroid lipid, while triglycerides are the main storage and dietary fat molecules.
- Assuming liquid oils are calorie free is wrong because oils are fats and still provide about 9 kcal per gram.
Practice Questions
- 1 A snack contains 12 g of fat. How many kilocalories come from fat in this snack?
- 2 A meal has 600 total kcal and 180 kcal from fat. What percent of the meal's calories come from fat?
- 3 Explain why olive oil and butter can both be fats but have different textures and health effects. Use the ideas of saturated and unsaturated fatty acids in your answer.