The potato paradox: Why ‘low sugar’ is not the same as ‘low GI’

Potatoes naturally contain relatively little simple sugar—but that does not automatically make every potato, or every potato dish, gentle on blood glucose. For consumers, growers, breeders and marketers, the distinction matters.

By Devendra K Jha, Founder of IndianPotato.com

Editor’s note: This article has been adapted for Potato News Today from an original article published by IndianPotato.com. It was submitted to the author for review before publication.

Potatoes have acquired an unusual reputation in modern food marketing. They may be promoted as low sugar, criticised as high glycaemic, selected by processors for low reducing sugars, or marketed as varieties capable of producing a lower blood-glucose response.

These descriptions may sound as though they are measuring the same thing. They are not.

A potato can contain relatively little simple sugar while still delivering a substantial quantity of starch. Because much of that starch may be rapidly digested into glucose after cooking, a “low sugar” claim does not necessarily tell consumers how the potato will affect their blood-glucose level.

This is the heart of the potato paradox: the phrase printed most prominently on a package may be the phrase that provides the least useful information about the consumer’s likely glycaemic response.

A potato is principally a store of starch

USDA FoodData Central figures for a generic raw potato, including flesh and skin, list approximately 17.5 grams of carbohydrate per 100 grams. Of this, about 15.3 grams are starch, while approximately 0.82 grams are sugars.

These figures can vary according to cultivar, maturity, growing conditions and storage history. Nevertheless, the broad relationship is clear: potato carbohydrate is overwhelmingly present as starch rather than simple sugar.

Using the USDA reference values:

Sugars account for approximately 4.7 per cent of total carbohydrate.
Starch represents roughly 87 per cent of total carbohydrate.
Starch outweighs sugars by approximately 19 to one.

Calling a potato “low sugar” may therefore describe an actual compositional characteristic. The problem is that consumers may interpret the claim as meaning low impact on blood glucose. That conclusion does not necessarily follow.

Once eaten, digestible potato starch is broken down into glucose. The amount of sugar originally present in the raw tuber is consequently only one small part of the metabolic picture.

What ‘low sugar’ means to a potato processor

Within the potato-processing industry, the word sugar often has a narrower and much more technical meaning. Processors are particularly concerned about the concentrations of the reducing sugars glucose and fructose.

Reducing sugars participate in the Maillard reaction during frying and other high-temperature cooking. This reaction helps create the familiar colour and flavour of fried foods, but excessive reducing-sugar concentrations can cause chips or French fries to become undesirably dark and bitter.

Reducing sugars also react with the amino acid asparagine during high-temperature processing, contributing to the formation of acrylamide. For that reason, processors carefully manage raw-material selection, storage and processing conditions.

The US Food and Drug Administration notes that reducing-sugar concentrations in potatoes are influenced by several factors, including:

Variety
Crop maturity
Growing and harvesting conditions
Handling practices
Storage temperature
Sprout control

A potato described in a processing contract as low in reducing sugars is therefore being assessed primarily for its processing behaviour, finished colour and acrylamide-forming potential. It is not automatically being classified according to its nutritional effect on blood glucose.

That distinction is easily understood inside a processing plant. It is much less obvious when similar language appears on consumer packaging.

Cold storage complicates the picture

Storage temperature can change the sugar composition of potato tubers. At sufficiently low temperatures, some cultivars convert a portion of their starch into reducing sugars—a physiological response commonly known as cold-induced sweetening.

The result may be a potato that stores acceptably but produces a darker fried product. Cultivar selection, storage temperature, reconditioning and approved sprout-management practices are therefore important parts of commercial storage programmes.

Sprout suppressants and their regulatory status differ between countries. Chlorpropham, or CIPC, was historically used extensively, but its approval was not renewed in the European Union, and the European potato industry has since moved towards alternative storage treatments and management systems. It would therefore be misleading to present any one sprout suppressant as the universal industry standard.

Whatever storage system is employed, the central distinction remains unchanged: managing reducing sugars for acceptable fry colour is not the same as selecting a potato for a lower glycaemic response.

Glycaemic index asks a different question

The glycaemic index, or GI, ranks carbohydrate-containing foods according to how rapidly they raise blood glucose under standardised test conditions. Pure glucose is assigned a value of 100.

The commonly used classifications are:

Low GI: 55 or below
Medium GI: 56 to 69
High GI: 70 or above

The 2021 International Tables of Glycemic Index and Glycemic Load Values, compiled by Fiona Atkinson and colleagues, demonstrate the considerable variation recorded among potato products and preparations.

Reported average figures cited in the IndianPotato.com analysis include:

Potato preparation	Reported GI	Classification
Cooked and refrigerated overnight	49	Low
Boiled	73	High
Mashed	79	High
Instant mashed potato	84	High

These figures should be interpreted carefully. They are compiled from different tested foods and studies—not from a single experiment in which one identical potato variety was prepared four ways. They nevertheless illustrate an important and well-established point: a GI value does not belong to the word “potato” in isolation.

Cultivar, starch composition, tuber maturity, processing, cooking method, physical structure and serving temperature can all influence starch digestibility and the resulting glycaemic response.

Why cooking and cooling can matter

Cooking generally gelatinises potato starch, making it more accessible to digestive enzymes. Mashing and intensive processing can break down the food’s physical structure further, which may help explain the relatively high GI associated with some mashed and instant potato products.

When a cooked potato cools, a portion of its starch can recrystallise through a process known as retrogradation. Some of this becomes resistant starch, which is not digested in the small intestine as readily as rapidly available starch.

Research has found that cooked and chilled potatoes can contain more resistant starch than freshly cooked potatoes. Some human feeding studies have also reported lower insulin or post-meal glucose responses under particular conditions.

The size of the effect is not identical in every study, however. Variety, cooking method, cooling time, reheating and meal composition may all influence the outcome. Cooking and cooling should therefore be understood as one potentially useful factor—not as a universal guarantee that a potato dish will produce a low glycaemic response.

Variety still has an important role

Preparation matters, but this does not mean that potato breeding and varietal selection are irrelevant.

The 2021 international GI review concluded that most tested potato varieties fell within the high-GI category, while also recognising that specific lower-GI cultivars have been identified. Differences in starch structure—particularly amylose and amylopectin characteristics—along with dry matter and resistant-starch content may contribute to varietal differences.

Lower-GI potatoes are now marketed in several countries, including India. However, a credible claim should be accompanied by enough information for buyers to understand what was tested.

At a minimum, suppliers should be able to answer:

Which cultivar or branded product was tested?
Was the GI determined by a recognised laboratory using an accepted human-testing protocol?
How was the potato prepared for testing?
What numerical GI value was recorded?
Was the result independently verified or based on a single test?
What comparison product or baseline was used?

A statement that one potato has a GI “30 per cent lower” than a conventional potato may sound impressive, but its meaning depends heavily on the comparison. A reduction from a baseline GI of 80 produces a different marketing impression than the same result expressed against another reference value.

The numerical result, test method and preparation should therefore accompany the claim.

GI is useful—but portion size also counts

Glycaemic index measures the quality or speed of available carbohydrate under standardised conditions. It does not, by itself, account for the amount of carbohydrate in the portion actually eaten.

Glycaemic load, or GL, combines GI with the grams of available carbohydrate in a serving:

GL = GI × available carbohydrate in the serving ÷ 100

This makes GL useful when moving from laboratory comparisons to actual meals. A smaller portion of a relatively high-GI food may produce a different overall glucose exposure from a large portion. The other foods in the meal—including protein, fat, fibre and vegetables—may also affect digestion and the post-meal response.

Individual responses vary as well. People managing diabetes or another medical condition should consequently rely on advice from a qualified healthcare professional rather than treating a retail claim as dietary guidance.

Four claims that should not be confused

Description	What it is measuring	What it does not establish
Low sugar	Naturally occurring simple sugars	The potato’s glycaemic response
Low reducing sugars	Glucose and fructose relevant to frying, colour and acrylamide formation	That the product is suitable for blood-glucose management
Low GI	The rate of blood-glucose increase under defined test conditions	The effect of every preparation or portion
Low glycaemic load	GI combined with carbohydrate in a specified serving	An individual consumer’s exact response

Better information would benefit the whole potato sector

Consumers are not wrong to ask for potatoes that fit their nutritional needs. The difficulty arises when industry terminology is transferred to consumer packaging without adequate explanation.

“Low sugar” may be technically accurate while providing little insight into the potato’s likely glycaemic effect. “Low reducing sugars” is valuable information for a processor but may be misunderstood by a household shopper. “Low GI” is more relevant to blood-glucose response, but only when supported by a numerical value, a credible testing method and a clearly defined preparation.

The potato industry can respond by communicating with greater precision. Retailers, breeders and suppliers should distinguish processing attributes from nutritional ones, publish substantiated test results and avoid allowing a simple front-of-pack phrase to carry more meaning than the evidence supports.

Potatoes remain nutritious, affordable and remarkably versatile foods. They should not be judged—or marketed—on one loosely defined word. In this case, the number, the method and the preparation tell consumers far more than the phrase low sugar ever could.

This article provides general industry and nutritional information and should not be regarded as individual medical or dietary advice.

About the author

Devendra K Jha is the founder of IndianPotato.com, an information and trade platform serving India’s potato value chain. This article developed from industry commentary concerning the use of “low sugar” terminology in Indian potato retailing. The original article acknowledged that SV Agri Processing Pvt Ltd, whose founder and managing director Hemant Gaur contributed to the discussion, markets a lower-GI potato. That commercial connection is retained here in the interests of editorial transparency.

Devendra’s LinkedIn profile can be viewed here. He can be reached at devenjha@gmail.com for further information.