Weight control: Glycaemic index (GI)

Jun 25th '24

What is the glycaemic index?

The glycaemic index (GI) is a rating system for foods containing carbohydrates according to their effects on blood sugar levels.


The GI takes the total available carbohydrate in a food into account. A food may contain fats and other components that result in a rise in blood sugar, the effects of which are not reflected in the GI.


The glycaemic load (GL) of food is a number that estimates how much the food will raise a person’s blood glucose level and is measured by multiplying the glycaemic index of the food in question by the carbohydrate content of the actual serving (Glycaemic load (GL) = GI of a food x amount carbohydrate in an average serving (g).


Factual statements of the GI value of a food should be based on that standard methodology, ideally measured in a laboratory that adheres to a suitable Quality Assurance scheme. Published tables list the GI of many commonly consumed foods (for example, Foster-Powell K et al, 2002). Committee of Advertising Practice (CAP) and the Advertising Standards Authority (ASA) are likely to use reputable published tables as a substitute for specific testing if the food in question is equivalent in nutritional content and extent or type of processing.



Classifications should be based on these established cut-offs:


Glycaemic index

  • High GI: 70 or more
  • Medium GI: 56 to 69
  • Low GI: 55 or less


Glycaemic load per meal or food

  • Low GL: 10 or less
  • High GL: 20 or more


Glycaemic load per day

  • Low GL for the day: 80 or less
  • High GL for the day: 120 or more


Claims for foods

CAP believes that it is inappropriate to make low GI claims for foods such as meat and unsweetened dairy products that contain few or no carbohydrates.


Low GI or low GL diets are not necessarily low in calories. Low GI foods may be recommended for weight loss only as part of a calorie-controlled eating plan and as part of a balanced diet.


The GI of a standard food can be altered by factors such as combining low GI foods with high GI ones to give a medium GI meal, the pH of the meal (for example, adding lemon juice lowers GI), processing, cooking or the presence or addition of amylose or amylopectins. The addition of ingredients to lower the GI of high-calorie or high-fat foods cannot be used as the basis of weight loss claims.


Marketers promoting a food (including soft drinks) or food supplements in relation to weight should take the Food Rules into account and note that weight loss and other claims of this nature, which directly result in an effect on one’s health, are considered to be health claims for the purposes of Section 15 of the Code. Article 2 of Regulation (EC) 1924/2006 on Nutrition and Health claims made for Foods, defines a health claim as “any claim that states, suggests or implies that a relationship exists between a food category, a food or one of its constituents and health…”


A health claim for a food should only be made if the claim is “authorised” and listed on the Great Britain nutrition and health claims (NHC) register (15.1). See Weight control: Food and Food supplements.


The claim “slow release energy” is likely to be considered a health claim and should comply with the Section 15 of the Code.


The ASA ruled that a claim that implied that, because fructose had a lower glycaemic index or load, it would provide the health benefit of a slower and lower rise in blood glucose levels compared to foods containing sucrose or glucose was a specific health claim and so should only be used if authorised. (Frank’s Ice Cream Ltd, 29 March 2023).


High fat, low carb diets might also fall under this definition.  As always, advertisers must ensure they don’t offer treatments for serious medical conditions, like obesity, and that any diet plans they offer are nutritionally well balanced.  Most importantly, they should ensure that any claims they make can be substantiated: Substantiation for health, beauty and slimming claims.   (ASC Twelve Ltd, 13 February 2019). Consumers are likely to understand changing or restricting what they eat to be a diet and marketers should therefore not describe such programmes as “not a diet” or similar (GS Phillips, 23 October 2019).


Source: CAP


About CAP

The CAP is the sister organisation of the Advertising Standards Authority (ASA) and is responsible for writing the Advertising Codes.


Note: This advice is given by the CAP Executive about non-broadcast advertising. It does not constitute legal advice. It does not bind CAP, CAP advisory panels or the ASA. CAP’s AdviceOnline entries provide guidance on interpreting the UK Code of Non-broadcast Advertising and Direct & Promotional Marketing.


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