What Is Starch and How Can It Make You Fat

Starch in foods is one of the most important concepts to understand if you are interested in using a low carb diet to lose weight. The term starch was used for years to describe complex carbohydrates but it went out of fashion when people started using the term carbs instead. A starch is a type of carbohydrate but it is not the only one, there is also sugar and fiber.

Starch is a carbohydrate which is made from a large number of glucose (sugar) molecules joined together. The bonds between these sugar molecules is fairly easily broken in the digestive tract and the result is a large amount of sugar being absorbed into the blood stream. This is a key to our current problems with weight gain in the US.

It is only recently that people have started to replace the term starch with the word carb. This change came because of several Low Carb diets on the market. They did not specify the difference between sugar, starch and fiber. Instead, these diets just limited all carbohydrates as if they all act on the body in the same way. But this is not really correct. Not all carbohydrates are starches, but it is true that all starches are carbohydrates.

The original low carb diets did not make a distinction between the different types of carbohydrates. It was thought that limiting all carbs would cause weight loss. This is true, but really only two of the three carbohydrate types will cause weight gain, sugar and starch. Fiber moves through the body undigested and thus can not cause weight gain. Fiber also is important for a healthy digestive tract and limiting it was one of the reasons many doctors did not like the idea of a no carb or low carb diet.

We now know that limiting sugar and starches are important because they are both digested into your body as blood glucose which is also known as blood sugar. The terms sugar and glucose are often times used to mean the same thing. They both are names for a simple sugar that is only one molecule in size. It is blood sugar (blood glucose) levels which cause havoc with diabetics and people who are overweight.

What Is Starch Made Of?

Starch is produced by all green plants as a way to store energy. Plants use chlorophyll (the green color in their leaves) to convert the energy from the sun and use it to combine carbon dioxide and water into sugar molecules. This sugar is used as fuel by the plants but not all of it can be used at once. It is much more effective for the plants to store groups of sugar packets instead of individual ones. So, the plants bond the sugars together to form long chain or branch molecules which are called starches.

What is starch

A representation of a starch molecule as several sugar molecules bonded together to form a chain


The picture above gives you an idea of how a starch molecule is formed. It shows several simple sugar molecules bonded together in a chain. When the starch is digested, the bonds between these sugar molecules is broken and the sugar is absorbed into the blood stream. You can see that starch is made up of sugar just waiting to be released.

These larger molecules are easier for the plant to store than simple sugar is. Some of the sugar is also converted to cellulose which is the structural component of plants. While cellulose is constructed of sugars just like starch, it can not be digested by humans because the sugars in cellulose are bonded together so tightly. This is known as insoluble fiber because it won’t even dissolve in water.

Starch Structure

A starch molecule can be either a long chain of simple sugar molecules laid end to end or they can branch out like branches on a tree. The key thing to understand about starches is that the sugar molecules are not held together very tightly and so our body can break them down easily. This is really the key idea that explaines why some carbohydrates make us fat and some don’t. The easier it is to convert the starch back to sugar the more sugar that is absorbed into our blood stream and the more sugar there is available to be converted into fat.

Every time we eat a plant we are eating starches and fiber along with some sugar molecules that have not been converted. When a plant based food tastes sweet you are tasting the sugars. Only plants can make starch which is why most low carb diets allow you to eat a lot of fish, poultry, and meat. There is no starch in these foods to be converted into sugar.

What Are Starch Foods

Foods that contain large amounts of starch include potatoes, wheat, corn and rice. It is also found in other grains like barley and oats and in beans. But not all of these starchy foods have the same effect on our bodies. That is, the starches in different foods break down at different rates into their sugars. This means some foods increase your blood sugar levels faster than other foods and thus they have more of an impact on whether you gain weight or lose it.

Two of the main factors that determine how fast a food is digested are the amount of fiber in the food and the amount of processing and cooking done to the food before it is eaten. When foods have a high fiber content along with the starch then the digestion is slowed down considerably. This is why one of the keys to a healthy eating lifestyle includes fiber at every meal.

Processing and cooking foods before eating acts like pre-digestion outside of the body. For example, some grains can not be digested by humans in their natural state because we don’t have the enzymes in our guts to break down the foods like certain other animals such as horses and cows do. In order for us to get any nutritional value out of these grains they need to be milled or crushed so we can digest them. But over-processing, which removes the fiber and protein and other nutrients, will make the starches too easy to digest.

For example, wheat kernels are not useful to us as they are found on the wheat stock so we grind them up in order to make them digestible. This is known as whole wheat because all the parts of the wheat are still in the flour. This includes the fiber which helps to slow down the rate at which the starches are digested. Whole wheat will still increase blood sugar levels but at a slower rate than white wheat.

The real problem occurs when wheat is processed to the point that it makes white bread and other bakery products. The starches are very easily digested with white bread and thus it leads to a quick increase in sugar levels. This is known as a sugar spike.

As I said above, it used to be thought that all carbohydrates were bad and were digested at about the same rate but that has been proven to be not true. Scientists have determined that different starchy foods digest at different rates. In order to compare the rate at which foods increase your blood sugar levels, the term “Glycemic Index” (pronounced gly-seem-ick) was developed.

First, the amount of rise in blood sugar levels when straight sugar water is digested was measured. This rate was given a value of 100. Every other food is then tested for the rate of sugar digestion and given a value based on this amount. So for example a Glycemic Index of 50 means it will only be digested and raise sugar levels half as much as the sugar water.

The Glycemic index of starchy foods allows us to compare how fast different foods are digested into their sugars. The higher the Glycemic Index number the quicker the sugar in the starch gets to our blood stream.

All foods have a Glycemic Index (GI) value even if it is zero. Meats, fish, and poultry do not have an appreciable effect on blood sugar so they have a value of zero. Most vegetables have a value which is below 35 on the index scale. The Glycemic Index of foods is very important to a healthy lifestyle because it measures how fast sugar will be introduced into our bodies from the food. We want to slow down the sugar increase as much as possible to help with weight loss.

This means we want to eat foods that have low values like meat, fish, poultry, and most vegetables. And we want to stay away from foods like potatoes, baked goods, rice, and corn. Beans are in the middle. They are starchy but the fiber evens out the speed at which the starches are digested.

What Are Resistant Starches

Resistant starches are ones that act like fiber and are not digested as they travel through the body. They also will slow down the absorbing of the sugars from regular starches. By combining resistant starches with regular starchy food you can have a control over how fast the sugar enters your blood stream.
Resistant starches actually pass completely through our digestive system without being digested at all. It acts like fiber in that the sugars are not released from the starch bonds and instead are kept intact. As you can imagine, resistant carbohydrates do no raise blood sugar levels.

Two Types Of Starch Molecules

The two main types of starch molecules are amylose and amylopectin. Most palnts are made up of about 20 to 25% amlyose and 75 to 80% amylopecin. Amylose is digested slower than the other form of starch and thus it has a lower Gycemic Index.

What About The Starch In Pasta

Pasta is made from grains so you would suspect that it would have a lot of starch, which is does, but there is an interesting phenomenon that occurs when it is made. Pastas such as spaghetti and macaroni are formed by forcing them through a die which creates the shape. This pressure seems to modify the starch to make it a little less digestible as long as the pasta is cooked in the al dente style which means slightly firm.

Pastas that are not formed by pressing through a die do not have this trait. These would be fettuccini, ravioli, and pastas that are cut from a rolled out sheet of dough. And, if you over cook formed pastas, then the benefit of the slower digested starch will disappear. So if you must have pasta choose spaghetti and macaroni and only cook it till it is just soft, not mushy.

Recap of What Are Starches

Starches are carbohydrates which are composed of simple sugar molecules stuck together. They are formed when plants need to store energy for later use. When we eat a plant food our bodies digest the starch back into the simple sugars which are then absorbed into our blood stream. Too much of this sugar can cause weight gain as it is stored as fat.

Not all starchy foods increase sugar levels at the same rate. The Glycemic Index is a number that tells us how fast the starch in a particular food is broken down into its sugar base and this sugar is digested. The lower the GI number the less of an effect the food has on our sugar levels.

Some starches called resistant starches can not be broken down in the digestive tract and are passed out of the body like fiber.

If you are over weight then one of the best things you can do for your body is to limit starches and sugars.