Difference between Sugar and Starch

Almost every person who has ever thought of healthy eating has heard that eating too much sugar is dangerous. Starch doesn’t have a good reputation among healthy lifestyle followers either. What is the difference between these two? Perhaps they have something in common as eating too much of either can lead to weight gain. In this article we are going to cover this issue.


The most important thing to know first is that sugars and starches are both carbohydrates. The difference is that sugars belong to the class of mono- and disaccharides (i.e. simple units of some molecules). Glucose, fructose and mannose – are sugars. Starches, on the contrary, have long molecular structures, combining sugar molecule subunits, and therefore are called polysaccharides. You can find more about this difference below.

Sugar vs Starch
Sugar molecule (glucose)

When hearing the word “sugar” many people immediately think of sparkly granules of table sugar. But in broader terms sugars mean any so-called “fast-acting” carbohydrates.

From the chemical point of view sugars are just carbon and water (the word carbohydrates is derived from this fact). Considering sugars and their functions it is clear that they are the primary source of energy to our bodies. In comparison to starches, sugar is a quick source of energy to cells. Glucose is human body fuel: fructose can be found in fruit and berries, galactose in milk and dairy products. These types of sugar are monosaccharides. To disaccharides belong sucrose – ordinary table sugar we add to dishes, or lactose – another type of milk sugar combining glucose and galactose. In reasonable amounts sugars won’t bring harm. They start forming fat deposits and negatively affect health and wellbeing only when over-consumed.

Unfortunately what has made sugars enemies for people who want to be fit is their abundance everywhere in the average diet nowadays. Excess amounts of sugar are found in sweets, bakery products, soda, creamy desserts and so on, in almost any food that is craved and considered unhealthy. Of course, there is some sugar in natural products, like fruits or honey. In moderate amounts these foods are healthy as they bring vital and quick energy to body cells. But overeating turns sugars into fat, regardless of what you eat in excess amounts: pastry or honey.

Simple sugars have a simple molecule and a formula like CxN2xOx, where C, H and O are carbon, hydrogen and oxygen respectively and x indicates a whole number of atoms. For example the chemical formula of glucose is C6H12O6.

Sugars are the same as simple or “fast-acting” carbohydrates and they always have a sweet taste. They act like an immediate energy source for muscles and organs (including the brain); therefore they need to raise blood glucose level quickly (what they actually do).

There are hardly any processed foods without any added sugars. The trickiest thing is that in most cases manufacturers don’t have to specify how much sugar they have added. And here is the greatest danger for processed foods lovers – they can easily exceed the level of recommended sugar intake. Health services and organizations recommend less than 70 g of sugar per day for males and under 50 g of sugar for females to remain healthy.

Sugars have poor nutrition value aside from quick energy, therefore they are often called “empty calories” as the sedentary lifestyle of modern people rarely requires the high sugar intake we are used to, especially if a person needs to lose some weight.

Among sources of simple sugars you should know the following:

  • Milk
  • Fruit
  • Honey
  • Fruit juices
  • Syrups (both natural and sold in supermarkets)
  • Regular table sugar

starch molecule

Starches (or polysaccharides) are hundreds of simple sugar molecules linked together. A very important thing is the configuration of the molecule. The same chemical formula may look different and create completely different products. For example both cellulose and starch are made of glucose, but starch can be easily digested by humans, while cellulose can’t.

Starches act as a primary energy storage unit for plants and animal organisms. Therefore many plants contain starch (like potatoes, carrots, red beet and some other). In human bodies energy is stored in glycogen; it is located as deposits in the liver and muscles until the moment there is a need for it. Glycogen is formed from glucose and breaks down into glucose too, so this is a true fuel stock.

Dietitians and nutritionists draw attention to the difference between different forms of starches. It is known that starches (except for highly refined ones) are long-digested or complex carbohydrates, because the body has to first break down the links between molecules to extract glucose and get energy from it. Therefore it takes time for breakdown. Unlike sugars, starches don’t increase  blood sugar level very rapidly.

The examples of healthy starches (complex carbs) are:

  • Oats
  • Whole wheat products
  • Other whole grains and products made from them
  • Starchy vegetables (potatoes, corn, peas)

Highly refined starches don’t belong to long-digested carbs and will immediately increase the blood sugar level acting like simple sugars. The most common examples are:

  • White bread
  • Cakes
  • Pastry

A high amount of fiber makes starches in foods take longer to break down into glucose, hence such foods are healthier. When it comes to choosing starchy foods (like rice, pasta or bread) it’s preferable to choose whole grain versions.

Sugar vs Starch

What’s the difference between sugar and starch? The most serious differences, as we mentioned above, are in their molecular structure and their energetic function.

Both sugar and starch are carbohydrates. Sugars stand for simple (or quickly and easily digested) carbs, and provide immediate energy to body cells. Sugars have a simple molecular structure and almost always have a sweet taste. Starches stand for complex carbohydrates (digested and absorbed over a longer period) and have a more complex molecular structure that affects the qualities of the starch type.

To put it simply, in nature sugar means rapid energy and starch means energy storage. In the process of digestion, starches get broken down into sugar (glucose). Glucose can form starch in the human organism (glycogen). So these two substances have a lot in common.

But when sugar and starch are consumed do they affect the blood sugar level the same way? And are “slow” and “fast” the only characteristics for their absorption? As we answered previously, sugars increase the glucose level quicker than unrefined starches. But another key point here is taking into account if other substances were consumed together with carbs. We are talking about fiber.

It slows down the absorption of both sugars and starches, but it forms the healthier food option with the latter. That is why not all starches are equal.

To sum up, it is necessary to say that all carbohydrates (including starches) have the same chemical structure of simple sugars, but the way these sugars are linked and how many of them are there is important.

Carbohydrates (starch and sugar) are an essential part of any diet and each has its functions. According to the World Health Organization, carbs should provide from 40% to 60% of all the food consumed. A small carb intake will make you feel tired and irritable, as the body needs fuel. Excessive carb intake will lead to overweight and health problems.

The correct amount of sugars and starches to consume depends on the everyday activity of each individual.

Comparison Chart

Sugar Starch
Simple carbohydrate Complex carbohydrate
Quicker absorbed Longer absorbed
Increases the blood level rapidly Increases the blood level gradually