Spot the Fat in Your Snack

Introduction

Do you love potato chips? If you do, you are not alone. Potato chips are a very popular snack food. In fact, many people eat more than one bag of chips per month. When eating potato chips, have you ever noticed that your hands get really greasy? Maybe you have heard people telling you not to eat potato chips because they are bad for you and contain too much fat. But is this really true? Do this activity and find out by making the fats in potato chips visible.

Background

Fats are a main component of our diet and are essential for our bodies to work. A healthy diet consists of about 20 percent fat. But why is fat useful to us? Well, body fat functions as an insulation layer to maintain our body temperature; it also protects our organs. Our body also uses fat for storing energy or for digesting essential fat-soluble vitamins. So why do we hear all these stories about bad fats that are unhealthy? The reason is that there are different types of fats in foods and not all of them are healthy.

If you have ever looked at nutrition labels of foods, you might have noticed that the fat category is subdivided into “saturated,” “unsaturated” and “trans” fats. The different names represent the different types of fats that result from different chemical structures of the fat molecules. But which of these are the “bad” and which are the “good” fats? Unsaturated fats—mostly found in plant-based foods and oils—have been shown to be beneficial to your health. Saturated fats—which mainly come from animal sources—have been associated with an increased risk of cardiovascular diseases. “Trans fats,” in particular, which come from food processing and do not occur in nature, should be avoided in a healthy diet.

Almost every food we eat has some amount of fat in it, often in an invisible form so we do not even notice it. Did you know that potato chips contain up to 35 percent fat? An easy way to make these fats visible is the so-called grease spot test. Grab some chips and see for yourself in this activity.

Materials

Preparation

Procedure

Observations and Results

Did you see some really big grease spots on the graph paper after crushing the chips? This is no surprise, as fat is a major ingredient in chips, as you probably noticed when you looked at their nutrition labels. When you just look at the chips, however, you do not necessarily see all the fat they contain. Only when you crumble the chips with your hands do you start to detect these invisible fats as your fingers become very shiny and slippery from all the grease.

When crushing the chips on the graph paper, a big grease spot should have appeared. If you held the paper against a light source, you saw that all the areas covered with grease became translucent. Why is that the case? The reason why fats produce grease spots is that they are non-volatile, meaning they have a very high boiling point and do not evaporate easily. In contrast to water, fats that get absorbed by paper cannot get enough heat to evaporate at room temperature. An easy way to test this is to take a sheet of paper and put one drop of oil next to a drop of water. First, both areas look wet and translucent, but after a while, the water will evaporate and the spot will dry, whereas the fat spot will remain visible. This is because when fat is absorbed into the paper’s pores, the paper—which is normally white due to scattering light that shines through—becomes less scattered, and therefore becomes darker in color and translucent.

When you compared the two different potato chip varieties, you probably observed that most of the squares were covered with fat for the regular chips and the underlying sheet of paper might even have had significant grease stains as well. Using the reduced fat chips, however, should have resulted in a much lower area covered with grease, both on the graph paper as well as on the sheet of paper underneath. This makes sense as these kind of chips contain less fat that can be absorbed by the paper. So next time you get a potato chip craving, remember the grease spots on the paper and maybe you will change your mind and reach for a less fatty snack instead…

Cleanup

More to Explore

• What is fat?, from TED-Ed
• Learning about fats, from KidsHealth
• How grease are your potato chips, from Science Buddies
• Science Activity for All Ages!, from Science Buddies

Credits